Final Report 

RTI Project No. 0215472 

FSIS Contract No. AG-3A94-D-16-0130 

May 18, 2018 

Food Safety Consumer Research Project: 

Meal Preparation Experiment Related to Thermometer Use 

Prepared For 

Chris Bernstein 

USDA, FSIS, OPACE, 

Food Safety Education Staff 

1400 Independence Ave., S.W. 

Washington, DC 20250-3700 

Prepared By 

Sheryl C. Cates 

Ellen Thomas 

Katherine Kosa 

RTI International 

3040 E. Cornwallis Road 

Research Triangle Park, NC 

27709-2194 

Benjamin Chapman 

Lisa Shelley 

Rebecca M. Goulter 

Minh Duong 

Margaret Kirchner 

Lydia Goodson 

Savana Everhart 

Lindsay Doring 

Lee-Ann Jaykus 

North Carolina State University 

Raleigh, NC 27695 

RTI Project Number 

0215472 

Food Safety Consumer Research 

Project: Meal Preparation 

Experiment Related to 

Thermometer Use 

Final Report 

May 18, 2018 

Prepared for 

Chris Bernstein 

USDA, FSIS, OPACE, 

Food Safety Education Staff 

1400 Independence Ave., S.W. 

Washington, DC 20250-3700 

Prepared by 

Sheryl C. Cates 

Ellen Thomas 

Katherine Kosa 

RTI International 

3040 E. Cornwallis Road 

Research Triangle Park, NC 27709 

Benjamin Chapman 

Lisa Shelley 

Rebecca M. Goulter 

Minh Duong 

Margaret Kirchner 

Lydia Goodson 

Savana Everhart 

Lindsay Doring 

Lee-Ann Jaykus 

North Carolina State University 

Raleigh, NC 27695 

Contents 

Section Page 

Executive Summary ES-1 

1. Introduction 1-1 

1.1 Background and Project Overview ..............................................................1-1 

1.2 Objectives of Meal Preparation Experiment Related to Thermometer Use ........1-2 

1.3 Organization of Report..............................................................................1-3 

2. Study Methods 2-1 

2.1 Meal Preparation Experiment Methodology ..................................................2-1 

2.1.1 Research Design ............................................................................2-1 

2.1.2 Study Procedures ...........................................................................2-1 

2.1.3 Pilot Testing ..................................................................................2-6 

2.2 Recruitment Procedures and Description of Final Sample...............................2-6 

2.3 Coding of Observation Data and Analysis ....................................................2-9 

2.4 Microbiological Data and Analysis.............................................................2-10 

2.5 Thermometer Data and Analysis ..............................................................2-10 

2.6 Post-observation Interviews and Analysis..................................................2-11 

3. Results 3-1 

3.1 Sample Characteristics .............................................................................3-1 

3.2 Intervention-Specific Results: Thermometer Use..........................................3-4 

3.3 Handwashing Compliance........................................................................3-12 

3.4 Cross-Contamination and Microbiological Analysis ......................................3-15 

3.5 Self-Reported Usual Practices for Thawing and Storing Leftovers..................3-20 

3.6 Participant Response to USDA Video on Thermometer Use (Treatment 

Group Only) ..........................................................................................3-22 

3.7 Additional Analysis .................................................................................3-26 

4. Discussion and Implications 4-1 

References R-1 

iii 
Appendices 

A: Screening Questionnaire ......................................................................................A-1 

B: Observation Script and Recipes.............................................................................B-1 

C: Post-observation Interview Guide..........................................................................C-1 

D: List of Equipment Provided in Each Test Kitchen .................................................... D-1 

E: Power Analysis....................................................................................................E-1 

F: Microbiological Methods........................................................................................F-1 

G: Observation Rubric............................................................................................. G-1 

iv 
Figures 

Number Page 

2-1. Study Procedures for Meal Preparation Experiment on Thermometer Use .............2-2 

3–1. Turkey Patty with Heat Maps Showing Thermometer Placement by Group ............3-7 

v 
Tables 

Number Page 

1-1. Research Questions, Data Sources, and Location of Results in Report ..................1-3 

2-1. Trigger Behaviors Used for Microbiological Sampling..........................................2-2 

2-2. Comparison of Demographic Characteristics for the U.S. Population (2014) 

with the Study Sample...................................................................................2-8 

3-1. Sample Characteristics...................................................................................3-2 

3-2. Rate of Thermometer Use ..............................................................................3-6 

3-3. Number of Patties for Which Temperature Was Checked Among Participants 

Who Used a Food Thermometer ......................................................................3-8 

3-4. Number of Flips per Patty (two patties per participant) ......................................3-8 

3-5. Time–Temperature Combinations for Turkey Patties Deemed Safe.......................3-9 

3-6. Distribution of Endpoint Temperatures Among Participants Who Used a Food 

Thermometer..............................................................................................3-10 

3-7. Methods Used to Determine Doneness for Participants Who Did Not Use a 

Food Thermometer ......................................................................................3-11 

3-8. Other Methods Used to Determine Doneness for Participants Who Did Use a 

Food Thermometer ......................................................................................3-12 

3-9. Handwashing Compliance.............................................................................3-14 

3-10. Reasons for Unsuccessful Handwashing Attempts............................................3-14 

3-11. Prevalence of MS2 Contamination and Level of Contamination for Four 

Locations in the Kitchen and Salad Lettuce .....................................................3-16 

3-12. Sequences of Contact Leading to Contamination Based on Prevalence and 

Level of Contamination for Mobile Phones (n = 6, out of 77).............................3-19 

3-13. Self-Reported Practices for Thawing and Storing Leftovers ...............................3-21 

3-14. Participants’ Responses to USDA Video on Thermometer Use............................3-23 

vi 
Executive Summary 

The Food Safety and Inspection Service (FSIS) of the U.S. Department of Agriculture 

(USDA) contracted with RTI International and its subcontractor North Carolina State 

University (NCSU) to conduct meal preparation studies to evaluate consumer food handling 

behaviors in a test kitchen. The research team is conducting five separate iterations of the 

meal preparation study to address a specific consumer behavior and to determine the 

effectiveness of a behavior change intervention. The meal preparation studies are part of a 

larger 5-year annual study that also includes focus groups (two iterations) and web surveys 

(two iterations). This report describes the results of the first iteration of the meal 

preparation study that examined consumers’ use of food thermometers when cooking 

ground turkey patties. 

RTI and NCSU conducted the study in six test kitchen facilities located in the metro RaleighDurham area of North Carolina and Smithfield, North Carolina, a rural location. Before 

preparing the meal, a randomized treatment group watched the 3-minute USDA food safety 

video “The Importance of Cooking to a Safe Internal Temperature and How to Use a Food 

Thermometer.” In each test kitchen, six cameras recorded participants’ actions at various 

locations throughout the kitchen and recorded the meal preparation from beginning to end 

of meal preparation. Participants in the control and treatment groups were observed while 

cooking turkey burgers (spiked with the harmless tracer bacteriophage MS2) and preparing 

a chef’s salad to determine whether they used a thermometer on the turkey products and 

whether they adhered to other food safety behaviors throughout the meal preparation. 

Following meal preparation and cleaning, the study team collected microbiological samples 

from surfaces and lettuce and analyzed the samples for prevalence and level of MS2. 

Participants participated in a post-observation interview to collect information on their usual 

food preparation practices and possible predictors of behavior change. A total of 383 people 

participated in the study (201 control, 182 treatment). 

The key findings from the study are summarized below: 

▪ Viewing the USDA video on thermometer use immediately before food preparation 

encouraged participants to follow USDA-recommended use of a food thermometer for 

checking doneness of raw poultry; however, more needs to be done to increase 

adherence to more nuanced recommended practices. 

– Participants who viewed the video (i.e., treatment group) were twice as likely to 

use a thermometer to check the doneness of the turkey patties compared with 

those who were not exposed to the video (i.e., control group) (75 vs. 34%). 

– Participants in the treatment group were twice as likely to place the thermometer 

in the correct location (i.e., the side of the patty to reach the center and coldest 

spot) compared with the control group (52 vs. 23% of attempts for thermometer 

placement). 

ES-1 
Meal Preparation Experiment Related to Thermometer Use 

– Participants in the treatment group were more likely than participants in the 

control group to cook the patties to at least 165°F (73 vs. 54%). 

– Use of other indicators of doneness was common among control group 

participants; most relied on only touch (the firmness or texture of the burger) or 

color and touch. 

– In the post-observation interviews, 66% of participants stated that watching the 

video influenced their cooking behavior in the kitchen; of these participants, 61% 

reported using a thermometer as a result of watching the video. 

▪ Proper handwashing, which was not addressed in the video, needs improvement. Of 

the 2,249 cases across all 383 observations in which a handwashing event was 

needed to decrease the risk of cross-contamination (e.g., before meal preparation 

and after handling raw product), participants attempted to wash their hands 31% of 

the time. Among attempted handwashing events, only 4% included all steps 

necessary to be considered an adequate handwashing event (defined by the Centers 

for Disease Control and Prevention’s recommended steps). 

▪ Improvements are also needed to reduce the risk of contaminating surfaces and 

ready-to-eat foods (not addressed in the video). Approximately 50% of participants 

contaminated spice containers they touched during the preparation of the preformed 

turkey burgers, and 6% contaminated the lettuce used to prepare the salad, a 

ready-to-eat food. This relatively low rate of contamination of the salad indicates 

that cross-contamination was not necessarily frequent but did occur with some 

regularity. 

Based on the study findings and previous work in the literature related to risk 

communication, we recommend that FSIS consider designing food safety messaging that 

▪ is clear and specific; 

▪ focuses on proper thermometer usage; 

▪ continues to emphasize handwashing and cross-contamination because 

improvements are needed in these areas; 

▪ tailors messages to audience needs, concerns, and interests; 

▪ stimulates perceptions of risk of illness from not following recommended food safety 

practices and bolsters self-efficacy for handling food safely; and 

▪ addresses behaviors that lead to the highest incidence of foodborne illness causing 

the most serious consequences such as cross-contamination, failure to cook to 

proper lethality temperature, and inadequate handwashing. 

There is a great deal more to learn about consumer attitudes and behaviors as they relate 

to food safety; understanding these factors will help FSIS better create awareness of safe 

food handling practices and be able to incorporate everyday contexts into food safety 

communications. 

ES-2 
1. Introduction 

This report describes the study methods and presents the results from a meal preparation 

study related to thermometer use, conducted as part of the Food Safety Consumer Research 

Project. The study, conducted in test kitchens, used an experimental design to measure the 

rate of thermometer use by consumers and level of adherence in cooking to recommended 

temperatures to compare behaviors between participants who received an educational 

intervention on thermometer use and those who did not. The thermometer use study is the 

first of five iterations of a meal preparation experiment in which consumers are observed 

while preparing meat and poultry products regulated by the U.S. Department of 

Agriculture’s (USDA’s) Food Safety and Inspection Service (FSIS). This report details our 

study design, data collection procedures, and data analysis approach and presents the 

results of the study for thermometer use, handwashing compliance, cross-contamination, 

and self-reported usual behaviors for thawing and storing leftovers. FSIS can use the results 

of this study to enhance consumer messaging on thermometer use. The rest of this section 

provides an overview of the Food Safety Consumer Research Project, describes the purpose 

of the initial meal preparation experiment, and details the organization of the report. 

1.1 Background and Project Overview 

USDA FSIS’s Office of Public Affairs and Consumer Education (OPACE) ensures that all 

segments of the farm-to-table chain receive valuable food safety information. The consumer 

education programs developed by OPACE’s Food Safety Education Staff inform the public on 

how to safely handle, prepare, and store meat, poultry, and egg products to minimize 

incidence of foodborne illness. 

OPACE strives to continuously increase consumer awareness of recommended food safety 

practices with the intent to improve food handling behaviors at home. OPACE shares its 

messages through the Food Safe Families campaign, social media, AskKaren (an online 

database of frequently asked food safety questions), the FSIS web site, FoodSafety.gov, the 

Meat and Poultry Hotline; publications, and events. These messages are focused on the four 

core food safety behaviors: clean, separate, cook, and chill. Additionally, OPACE’s public 

education and outreach initiatives reach vulnerable and underserved populations. 

By testing new consumer messaging and tailoring existing messaging, FSIS can help ensure 

that it is effectively communicating with the public and promoting behavior change with a 

goal of improving consumer food safety practices. FSIS contracted with RTI International to 

conduct consumer research over a 5-year period, fiscal year 2017 through fiscal year 2022. 

RTI is teaming with researchers at North Carolina State University (NCSU) to conduct the 

project. This behavioral research will include observation studies of food preparation in test 

kitchens using an experimental design (five iterations), focus group studies (two iterations), 

1-1 
Meal Preparation Experiment Related to Thermometer Use 

and web surveys (two iterations). Each iteration of each data collection activity will address 

different research questions and use a different sample of consumers. This research will 

provide insight into the effect FSIS consumer outreach campaigns have on consumers’ food 

safety behaviors. FSIS will use the results of this research to enhance messaging and 

accompanying materials to improve food safety behaviors of consumers. Additionally, this 

research will provide useful information for tracking progress toward the goals outlined in 

the FSIS fiscal years 2017–2021 Strategic Plan (USDA, FSIS, 2016). 

1.2 Objectives of Meal Preparation Experiment Related to 

Thermometer Use 

Previous research suggests that self-reported data collected through surveys on consumers’ 

food safety practices are unreliable because consumers tend to overreport their behavior 

(e.g., simply rinsing their hands instead of washing with soap and water for 20 seconds as 

recommended) (Redmond & Griffith, 2003). Because of this limitation, observation is a 

preferred approach for collecting information on consumers’ actual food safety practices. 

Studies that have used direct observation of consumer food handling have reported that 

many consumers commit errors during preparation and self-report different actions 

(Anderson et al., 2004; DeDonder et al., 2009; Jay, Comar, & Govenlock, 1999; Kendall et 

al., 2004; Redmond, Griffith, Slader, & Humphrey, 2004). The results of the meal 

preparation experiments will help FSIS assess adherence to the four recommended food 

safety behaviors of clean, separate, cook, and chill; determine whether food safety 

messaging focused on those behaviors affects consumers’ safe food handling behaviors; and 

determine whether consumers introduce cross-contamination during food preparation. 

Each iteration of the meal preparation experiment addresses a specific consumer behavior; 

the first iteration examined consumers’ use of food thermometers when cooking ground 

turkey patties. Participants randomized to the control or treatment group (exposed to 

intervention on thermometer use) were asked to cook turkey burgers and prepare a chef’s 

salad as they would at home. We observed participants throughout this entire process to 

determine whether they used a thermometer and whether they adhered to other food safety 

practices such as handwashing. This study also assessed pathogen transfer during meal 

preparation, measured the temperature of cooked patties using a data logger to determine 

whether a safe endpoint temperature was achieved, and included the collection of 

microbiological samples from lettuce (lettuce used as garnish for prepared burgers or 

lettuce from the prepared salad) and kitchen surfaces. A post-observation interview 

collected information on consumers’ reasons for following or not following recommended 

food safety practices and self-reported data on practices that could not be observed such as 

thawing and storing leftovers. 

Table 1-1 lists the study’s research questions, data sources, and the corresponding section 

of this report with the results of the analysis conducted to address each research question. 

1-2 
Section 1 — Introduction 

Table 1-1. Research Questions, Data Sources, and Location of Results in Report 

Research Question Data Source Location in Report 

Is the rate of thermometer use higher for the 

treatment group compared with the control 

group? 

Observations Section 3.2, Table 3-2 

Are participants in the treatment group more 

likely to use a food thermometer correctly 

compared with the control group? 

Observations Section 3.2, Figure 3-1, 

Tables 3-3 and 3-4 

Among participants who use a food 

thermometer, what percentage cook the 

patties to a safe temperature? 

Data logger Section 3.2, Tables 3-5 

and 3-6 

What methods are used to determine 

doneness in lieu of a food thermometer for 

the control and treatment groups? 

Observations, screening 

questionnaire 

Section 3.2, Tables 3-7 

and 3-8 

What is the rate of successful handwashing 

attempts for the control and treatment 

groups? What are the reasons for 

unsuccessful handwashing attempts? 

Observations Section 3.3, Tables 3-9 

and 3-10 

What are the prevalence and the levels of 

contamination of kitchen surfaces and lettuce 

Microbiological sampling 

data 

Section 3.4, Tables 3-11 

and 3-12 

for the control and treatment groups? When 

contamination is found, what sequence of 

events led to the contamination? 

What are the rates of various thawing 

methods usually followed as reported by 

participants in the treatment and control 

groups? 

Post-observation 

interviews 

Section 3.5, Table 3-13 

What are the rates of various leftover storage 

practices usually followed as reported by 

participants in the treatment and control 

groups? 

Post-observation 

interviews 

Section 3.5, Table 3-13 

What elements of the intervention video are 

effective at encouraging participants to follow 

recommended practices? (treatment group 

only) 

Post-observation 

interviews 

Section 3.6, Table 3-14 

1.3 Organization of Report 

This report is organized as follows: 

▪ Section 2 describes the research design, data collection procedures, and analysis 

approach. 

▪ Section 3 presents and discusses the results of the study for thermometer use, 

handwashing compliance, cross-contamination, and other behaviors. 

▪ Section 4 concludes the report by discussing the implications of the study results for 

FSIS’s consumer food safety education and outreach efforts. 

1-3 
Meal Preparation Experiment Related to Thermometer Use 

The appendices are organized as follows: 

▪ Appendix A: Screening questionnaire for participation in study 

▪ Appendix B: Observation script and recipes 

▪ Appendix C: Post-observation interview guide 

▪ Appendix D: List of equipment provided in each test kitchen 

▪ Appendix E: Power analysis to determine sample size for study 

▪ Appendix F: Microbiological methods (provides complete description of the selection 

of the surrogate and the microbiology methodology) 

▪ Appendix G: Observation rubric for coding participant actions in the kitchen 

1-4 
2. Study Methods 

This section describes the methodology for the meal preparation experiment; describes the 

recruitment procedures and the final sample; and details the approach for coding and 

analyzing the observations, collecting and analyzing the microbiological samples, and 

analyzing the post-observation interview data. The Office of Management and Budget (OMB 

control number 0583-0169, expiration date 6/30/2018) and North Carolina State 

University’s Institutional Review Board (IRB) approved the study protocol and materials. 

2.1 Meal Preparation Experiment Methodology 

2.1.1 Research Design 

The first meal preparation experiment focused on the food safety behavior of “cook,” 

specifically whether participants used a food thermometer to check doneness of turkey 

patties and whether the patties were cooked to the recommended temperature. We 

randomly assigned participants to a control group (no exposure to food safety messaging) 

or an intervention (treatment) group. 

We calculated the sample size to determine the minimum number of participants needed to 

provide a level of confidence that the meal preparation experiment was sufficiently 

powered, meaning that a change of the anticipated size or greater would be interpreted as 

occurring beyond chance (i.e., statistically significant). Based on the power analysis (see 

Appendix E), the desired sample size was 400 (200 per group) to provide 80% statistical 

power and a 95% level of confidence. The sample size calculation took into consideration 

the anticipated base rate for thermometer use and the anticipated distributional 

characteristics of a dichotomous outcome and the research design that is feasible given the 

logistical constraints of conducting test kitchen observations in one location. 

2.1.2 Study Procedures 

Figure 2-1 summarizes the study procedures. We conducted the study in six test kitchen 

facilities located in the Raleigh-Durham area of North Carolina (Wake County) and 

Smithfield, North Carolina, a rural location (Johnston County). In each test kitchen, six 

cameras recorded participants’ actions at various locations throughout the kitchen and 

recorded the meal preparation from beginning to end. Observers monitored the cameras 

throughout the process to identify any trigger behaviors for the microbiological sampling. 

Trigger behaviors are actions that could potentially lead to cross-contamination (see 

Table 2-1). 

2-1 
Video Recording 

Coding and 

Notational Analysis 

Final Report and Dissemination 

Recruit Participants 

• Treatment (n=200) 

• Control (n=200) 

Cooking Task 

• Raw Meal/Poultry 

• RTE Food 

Post-observation 

Interviews 

Cleanup 

Real-Time 

Observation 

l 

M icrosampling 

I Analysis of 7 •f------------,1 Microsamples 

Meal Preparation Experiment Related to Thermometer Use 

Figure 2-1. Study Procedures for Meal Preparation Experiment on Thermometer 

Use 

Table 2-1. Trigger Behaviors Used for Microbiological Sampling 

Trigger Options 

Handwashing ▪ Washed hands thoroughly 

▪ Did not wash hands thoroughly/Did not wash hands 

Hand drying ▪ Dried hands after washing using paper towels 

▪ Did not use paper towels to dry hands 

Packaging ▪ Did not move packaging for ground turkey patty around in food preparation 

area 

▪ Moved packaging for ground turkey patty around in food preparation area 

Handwashing ▪ Washed hands after handling raw ground turkey patty 

▪ Did not wash hands after handling raw ground turkey patty 

Turkey rinsing ▪ Did not wash or blot/dab ground turkey patty 

▪ Washed ground or blot/dab turkey patty 

Thermometer use ▪ Used thermometer on ground turkey patty 

▪ Did not use thermometer on ground turkey patty 

Produce washing ▪ Washed produce after handling ground turkey 

▪ Did not wash produce 

Cutting board use ▪ Did not use the same cutting board and plates for produce and ground 

turkey patty 

▪ Used same cutting board and plates for produce and ground turkey patty 

(continued) 

2-2 
Section 2 — Study Methods 

Table 2-1. Trigger Behaviors Used for Microbiological Sampling (continued) 

Trigger Options 

Knife use ▪ Did not use same knife for produce and ground turkey patty 

▪ Used same knife for produce and ground turkey patty 

Use of device ▪ Did not touch device (e.g., phone) 

▪ Touched device (e.g., phone) 

Cutting board ▪ Washed cutting board and utensils with soap and water 

wash step ▪ Did not wash cutting board and utensils with soap and water 

Drying equipment ▪ Dried kitchen equipment (cutting boards, knives) with paper towels 

▪ Did not dry kitchen equipment with paper towels 

Note: The recommended (safe) practice is listed as the first option. 

We used convenience 

sampling to recruit Six cameras 

participants using a variety in each test 

of approaches. Section 2.2 kitchen 

recorded describes the participant participant screening criteria and behaviors 

recruitment procedures. during meal 

preparation. Participants were told they 

would receive a $75 gift 

card and gift (food 

thermometer) for taking 

part in the 2-hour study. 

Participant recruitment began July 5, 2017. We scheduled observation appointments 

starting August 2, 2017, and ending December 22, 2017. 

We randomly assigned participants to the treatment or control group when the appointment 

was scheduled, with the goal of 200 participants in each group. Before the scheduled 

appointment for the meal preparation experiment, each participant received a reminder 

email with a confirmation of location, time, and check-in procedures. The email also 

included a link to a short YouTube video that explained what participants could expect to 

take place during the study and the meal they would prepare, along with some visuals on 

raw product and finished meals (referred to as the expectation video). Additionally, the 

confirmation email for the treatment group instructed participants to click on a link to the 

USDA YouTube video “The Importance of Cooking to a Safe Internal Temperature and How 

to Use a Food Thermometer,”1 which served as the intervention. Participants were also 

1 https://www.youtube.com/watch?v=-2KkV2yFiN0 

2-3 
nie Importance of cooking to a safe Internal le·mperature and How to u~ a F'ood "Thermometer 

59 201 v~w, •• ,, .. H 

1,1-Fi:%1 

Meal Preparation Experiment Related to Thermometer Use 

shown the video before beginning the study, explained below. This video focuses on the 

following messages: 

▪ Visual cues are not sufficient to assess safety. 

▪ A proper internal temperature is needed. 

▪ The only way to ensure safety is to use a food thermometer. 

▪ When finished, clean food thermometer with soap and water. 

For the hamburger patty portion of the video, flipping is shown, inserting the thermometer 

from the side is demonstrated, and the message provided is to measure the temperature for 

each patty. 

We recruited participants and scheduled their appointments at one of the test kitchen 

locations. Upon arrival to the test kitchen, a study team member greeted participants and 

instructed them to read USDA video on 

thermometer and sign an informed use served as 

consent form. A study the intervention 

team member gave 

participants in the 

treatment and control 

groups iPads upon 

entering the observation 

waiting area and asked 

them to view the 

expectation video. Using 

a video provided 

consistency in delivering this information. To ensure exposure to the intervention, treatment 

group participants viewed the USDA video on thermometer use before beginning to cook. 

Initially, we told participants the purpose of the study was recipe testing. Consistent with 

the approach used in other observation studies, we informed participants of the real 

purpose of the study following the meal preparation and why it was important from a 

scientific perspective to inform them after the study was complete2 (Chapman, Eversley, 

Fillion, MacLaurin, & Powell, 2010; DeDonder et al., 2009). 

A study team member gave participants a laminated recipe card—one side had a chef’s 

salad recipe and one side had a turkey burger recipe (with a lettuce and tomato garnish)— 

and instructed them to prepare the foods as they would at home (see Appendix B for a copy 

of the scripts and recipe). Participants were not told which item to prepare first (burger vs. 

salad). A study team member pointed out that cabinets containing utensils, dishes, pans, 

2 After being informed of the study’s purpose, participants had the option to opt out of the study; if 

they did opt out, we did not use their data. 

2-4 
Section 2 — Study Methods 

and a George Foreman grill were labeled accordingly (see Appendix D for a complete list of 

equipment provided in each test kitchen and a picture of one of the test kitchens). 

Recording of a participant’s handling and meal preparation began as soon as the participant 

entered the test kitchen and ended when the participant exited. Study team members also 

recorded participants’ cleaning and sanitizing of the kitchen equipment and surfaces after 

meal preparation. 

We used the tracer bacteriophage MS2 in this study because it (1) is completely harmless to 

humans because it infects only its bacterial host; (2) has a long history of use as a 

microbiological indicator; (3) is easy to culture and detect/enumerate by real-time 

polymerase chain reaction (RT-qPCR); and (4) unlike bacterial surrogates, requires no 

additional environmental health and safety documentation, such as a biological use 

authorization approval, for its use in NCSU test kitchens, which was an important 

consideration given the time constraints for conducting the first iteration of the study.3 

Before the study, we inoculated the turkey patties with the tracer bacteriophage MS2 at a 

level of 1010 per gram of ground turkey meat using a Kitchen Aid mixer. We confirmed 

homogenous levels of MS2 throughout the ground turkey mixture by testing random 

samples of the meat-MS2 mixture on turkey patty production days. The purpose of the 

surrogate was to track any potential cross-contamination from raw turkey patties to various 

locations around the kitchen and to a ready-to-eat (RTE) salad during meal preparation in 

the test kitchens. Appendix F provides a complete description of the selection of the 

surrogate and the microbiology methodology. We gave each participant two turkey patties 

packaged in a styrofoam tray with clear plastic wrap and with a mock label and the USDA 

Safe Handling Instructions to resemble patties purchased at a grocery store. 

During data collection, trained sample collectors sampled a 10 x 10 cm counter space area 

(sample “Time 0”) to ensure the kitchen space was sterilized effectively (MS2 contamination 

removed) before each participant entered the kitchen. Following the observation, trained 

sample collectors collected surface swab samples from kitchen surfaces, utensils, food 

containers, appliance handles, kitchen towels, and cutting boards (in all observations) for up 

to 12 samples (see Appendix F, Attachment 1—Sample Collection Form). The RTE salad dish 

was only sampled if the participant prepared it after preparing the turkey burgers; if the 

salad was prepared before the burgers, then lettuce from the burger garnish was collected 

instead. If a participant handled their mobile device during meal preparation, we took a 

swab sample from the device if the participant gave permission. An NCSU lab processed the 

swabs to determine the presence and concentration of the MS2. The presence of MS2 

indicated that cross-contamination occurred during food preparation. We compared the level 

of cross-contamination across the sampling sites to determine the highest risk areas. We 

cleaned and sanitized all accessible kitchen surfaces (e.g., counters, drawer pulls, stove 

3 For the initial study, we did not use a bacteria surrogate because of the lengthy review process that 

would be required. 

2-5 
Meal Preparation Experiment Related to Thermometer Use 

top), appliances, and other sites after each participant to ensure that any potentially 

remaining MS2 contamination was removed before the next participant entered the kitchen. 

The study protocols detailed consistent methods for conducting the observations and for 

collecting samples. 

Supplementing the observations, we conducted post-observation interviews to provide 

insight into participants’ views, opinions, and experiences during the meal preparation 

experiment, with questions based on the trigger behaviors that were observed during food 

preparation. The interviews also collected information on behaviors that we were unable to 

observe (e.g., storage of leftovers or thawing) and information on antecedents such as 

concerns about food safety and previous experience with foodborne illness. Interviews 

lasted approximately 20 minutes (see Appendix C for the post-observation interview guide). 

2.1.3 Pilot Testing 

Before initiating the full-scale data collection, we conducted two pilot studies to test the 

study materials, procedures, and the time allotted for data collection. We conducted the first 

pilot with two food science students as subjects and the second pilot with one subject 

recruited by convenience sampling. Representatives from FSIS participated in each pilot 

study. Based on these pilots, we made several modifications to update the recipes and 

script to provide clearer information to participants, added behaviors to the list of triggers, 

and updated the list of needed ingredients and kitchen equipment. Before the data 

collection began, we revised the materials and updated the study’s Standard Operating 

Procedures document. 

2.2 Recruitment Procedures and Description of Final Sample 

The study team used convenience sampling with quotas to help ensure that study 

participants reflected the demographic characteristics of the U.S. population based on the 

most recent Census data. We recruited participants using social media outlets (e.g., 

Facebook, Craigslist), by sending emails to Expanded Food and Nutrition Education Program 

(EFNEP) participants to reach low-income consumers, and by posting and distributing flyers 

about the study in approximately 150 locations within driving distance of the test kitchens 

located in Raleigh, North Carolina, and Smithfield, North Carolina. Flyers were 

posted/distributed in locations where low-income and older adults may congregate such as 

churches, community centers, libraries, and food pantries. The study team faced challenges 

recruiting people with a high school education or less, adults 55 years or older, and Hispanic 

people; thus, we requested and received OMB approval the last month of data collection to 

use outbound recruiting to recruit participants and to conduct the study in Spanish. We 

worked with a local market research firm to contact individuals in their database with the 

desired demographic characteristics (i.e., high school, age 55 years or older, and/or 

Hispanic) and to screen the individuals for eligibility. Additionally, we translated the 

recruitment materials into Spanish and posted the recruiting materials in Spanish on 

2-6 
Section 2 — Study Methods 

Craigslist and in the Que Pasa Raleigh newspaper, as well as conducted outreach at 

locations in which Hispanic people may congregate such as Hispanic grocery stores, 

churches, and community organizations including The Hispanic Family Center. 

Participants had to meet specific inclusion and exclusion criteria. The inclusion criteria were 

as follows: 

▪ age 18 or older 

▪ speak English or Spanish 

▪ do all or most of the grocery shopping in the household 

▪ prepare meals at home at least 4 times a week 

▪ cooked raw meat or poultry at home in the past 3 months 

The exclusion criteria were as follows: 

▪ have ever received any type of food safety training, such as ServSafe 

▪ have ever been employed as a food worker or manager in a food preparation setting 

▪ are vegetarian or vegan 

Recruitment materials directed prospective participants to call or email the study team to be 

screened for eligibility or to a web link that hosted the screening questionnaire (see 

Appendix A). For participants screened by phone, we invited eligible participants to 

participate in the study and scheduled an appointment during the screening call. For 

participants who completed the web-based screener, we contacted eligible participants by 

phone, invited them to participate in the study, and scheduled an appointment. We told 

participants that study participation involves preparing several recipes and participating in a 

short interview. Appointments were scheduled during work hours, evenings, and weekends 

to allow for a broader participant pool. After an appointment was scheduled, we sent a 

confirmation email or letter and made a reminder call 1 or 2 days before the scheduled 

appointment. 

Table 2-2 provides the target number of participants by demographic characteristic based 

on 2014 Census data and the actual number of participants in the sample. A total of 383 

people participated in the study; thus, we fell slightly short of the target of 400 participants. 

The demographic characteristics of the participants differed from Census data targets 

primarily in terms of education level and family (i.e., children in the household) versus 

nonfamily household (i.e., no children) status. The percentage of participants with less than 

high school or high school diploma/GED was 24% compared with the Census target of 42%. 

This difference was a result of the local population’s higher educational attainment, initial 

classification of technical/vocational training in the “some college” category, and higher 

screen-out rates due to food safety training and food industry experience for the less than 

2-7 
Meal Preparation Experiment Related to Thermometer Use 

Table 2-2. Comparison of Demographic Characteristics for the U.S. Population 

(2014) with the Study Sample 

Target Number Actual Number 

of Participants (Percentage) of 

Percentage based on Participants in 

from Census Census Data Study Sample 

Characteristic Dataa (n = 400) (n = 383) 

Race 

White 74% 296 253 (66%) 

Non-Whiteb 26% 104 130 (33%) 

Ethnicity 

Not Hispanic or Latino 83% 332 330 (86%) 

Hispanic or Latino 17% 68 53 (14%) 

Age 

18–34c 28% 112 134 (35%) 

35–54 36% 144 154 (40%) 

55+ 36% 144 95 (25%) 

Education 

Less than high school or high school 42% 168 93 (24%) 

diploma/GEDd 

Some college 29% 116 99 (26%) 

Bachelor’s degree 18% 72 119 (31%) 

Graduate or professional degree 11% 44 72 (19%) 

Household statuse 

Family household (children) 66% 264 176 (46%) 

Nonfamily household (no children) 34% 136 207 (54%) 

a Source: U.S. Census Bureau. (n.d.). 2010-2014 American Community Survey 5-year data profiles. 

Retrieved from https://www.census.gov/acs/www/data/data-tables-and-tools/data-profiles/2014/ 

b Non-White includes Black or African American, American Indian or Alaska Native, Asian, Native 

Hawaiian and Other Pacific Islander, other races, or 2 or more races. 

c For the Census data, the first age category was 20–34 years, instead of 18–34 years. 

d During the last month of data collection, we changed this category to include participants who may 

have completed one or more classes as part of a technical or vocational training program (e.g., 

welding, refrigeration, cosmetology). 

e For the Census data, family household includes households with children 18 years or younger; 

married-couple families; male householder, no wife; and female householder, no husband. 

Nonfamily household includes people living alone and people 65 years or older. For the current 

study, we classified a participant as a family household if the participant had a child less than 18 

years of age living at home. 

2-8 
Section 2 — Study Methods 

high school/high school/GED population.4,5 The percentage of participants from a nonfamily 

household was 54%, yet the Census data target for this category was 34%. The difference in 

our study population was likely due to a higher percentage of participants (35%) in the 18 to 

34 years age category. More highly educated respondents were recruited and scheduled first, 

which made it more difficult to recruit people from other target demographic groups (e.g., 

high school, Hispanic, and 55 years or older), resulting in the need for outbound recruiting. 

Although the Census targets were not met, the study sample is still diverse regarding the 

demographic characteristics of interest. 

The eligibility rate (percentage of cases that completed the web-based or phone screening 

and met the eligibility criteria) was 36%. For prospective participants completing the webbased survey, we screened out approximately 12% because they did not do all or most of 

the grocery shopping for the household. Of the potential participant pool at this point, we 

then screened out approximately 16% because of prior food safety training (e.g., ServSafe) 

and then 12% of this potential population because of work experience in the food industry. 

Among the 383 study participants, we recruited 58% using social media, 18% via outbound 

recruiting efforts, and 8% via posters and flyers; thus, social media was much more effective 

than using posters and flyers to recruit participants. The expected response rate (show rate) 

for the kitchen preparation study was 80%; the actual show rate averaged 85%. 

2.3 Coding of Observation Data and Analysis 

We used notational analysis to assess recorded actions and their frequencies. Notational 

analysis is a generic tool used to collect observed events and place them in an ordered 

sequence (Hughes & Franks, 1997); it has been used to track food safety behaviors, 

because it enables the recording of specific details about events in the order in which they 

occur by associating a time stamp with actions (Clayton & Griffith, 2004). Using a timestamp is especially useful when looking at sanitation steps limiting cross-contamination or 

the use of common food contact surfaces and equipment. Notational analysis has been used 

in both nonparticipant and participant consumer food safety behavior observation studies, 

as well as participant foodservice observation (Chapman et al., 2010; Clayton & Griffith, 

2004; Green et al., 2006; Redmond et al., 2004). 

We developed separate coding rubrics to characterize the following behaviors: 

▪ handwashing 

▪ thermometer use 

4 The average screen-out rate for food safety training and food industry experience for the high 

school/GED population was 48% compared with 30% in the “some college” demographic, 26% in the 

“college degree” demographic, and 21% for the “postgraduate degree” demographic. 

5 The educational attainment levels in Wake County are higher relative to the U.S. population: 50% of 

adults in Wake County have a bachelor’s degree compared with 18% for the U.S. population (U.S. 

Census Bureau, 2016). 

2-9 
Meal Preparation Experiment Related to Thermometer Use 

▪ direct cross-contamination 

▪ indirect cross-contamination 

Observers followed the rubric to indicate level of adherence to recommended behaviors 

while observing participants. The rubric also included a list of trigger behaviors that 

prompted additional questions during the post-observation interview and items to be 

sampled. Coders were trained by reviewing the coding rubric and using practice food safety 

handling scenarios to compare inter- and intracoding reliability. Incorrect and inconsistent 

coding situations were discussed with coders to ensure that proper and consistent training 

occurred. Appendix G provides the coding rubrics. 

2.4 Microbiological Data and Analysis 

We determined the concentration of MS2 on swab samples by comparing RT-qPCR results 

with a standard curve. We determined a swab sample was significantly contaminated if it 

contained 5 log10 MS2 RT-qPCR genome equivalent copies (GECs) or higher. We would not 

expect contamination levels of pathogens in USDA regulated food products to exceed 5 

log10, in step with data-supported assumptions found in 9 CFR Parts 301, 317, 318, 320, 

and 381. To confirm effective decontamination of the kitchen between participants, one 

cleaning validation surface swab was taken before a participant began their meal 

preparation. A total of up to 12 surface samples and one lettuce sample were taken for each 

observation, resulting in up to 14 total samples per observation. The results provided in this 

draft report describe the prevalence and level of contamination of the RTE salad, mobile 

device (if used), refrigerator handle, faucet handle and spice containers. Further analysis is 

being conducted on remaining samples, and data will be provided in a supplement to this 

report in July 2018. Appendix F provides additional information on the microbiological 

analysis procedures. 

2.5 Thermometer Data and Analysis 

A trained observer viewed each video to assess thermometer usage frequency, correct 

placement, and specific temperatures. We created a heat map to show not only the 

approximate placement of the thermometer when placed into each the patty, but also the 

angle of insertion (whether from the top, directly from overhead, or from the side) as 

observed during the study. We also constructed a unique instrument for this project: a data 

logger placed inside the housing of a thermometer constructed to look like a commercially 

available thermometer for consumer use. When participants used the thermometer/data 

logger, it recorded the temperature of the probe tip every second. In addition to the 

placement and temperature, observers also recorded whether the thermometer was used on 

one or two patties (because often the temperature varies between patties). Supplemental to 

the thermometer use, observers also recorded the number of flips per patty, because 

flipping can lead to more even heating of the product. 

2-10 
Section 2 — Study Methods 

2.6 Post-observation Interviews and Analysis 

The post-observation interviews collected information on participants’ decisions while 

cooking the meal and information about their food handling behaviors that were not 

observed (Appendix C provides the interview guide). We audio recorded the interviews and 

had typed transcripts prepared using the service TranscribeMe. We coded the transcripts 

and analyzed the data using QSR International NVivo, Version 11 software. 

We administered separate interview guides for the treatment and control groups. 

Participants in the treatment group answered questions about their reaction to the 

thermometer video that they watched before cooking and the extent to which watching the 

video influenced their actions in the kitchen. Control group participants, who did not watch 

the thermometer video, answered questions about how they get information about safely 

preparing foods and preferred methods for receiving such information. 

Questions posed to all participants during the interview were influenced by the trigger 

behaviors that were observed during meal preparation (see Table 2-1) and related to 

▪ handwashing, 

▪ determining doneness (including thermometer use), 

▪ handwashing after touching raw turkey or packaging, 

▪ washing cutting board and utensils, and 

▪ touching personal mobile devices while cooking (if applicable). 

For each behavior, the interviewer prompted the participant based on the actions observed 

and asked why he or she did the behavior and whether that is a behavior he or she typically 

does at home. 

Following data collection and transcription, analysts uploaded the transcripts from all 

recorded interviews into NVivo for coding and analysis. We assigned a unique case number 

to each participant to link the screener data and post-observation data. We coded the 

following variables presented in this report: 

▪ food poisoning: 

– participant ever experienced food poisoning 

– family member of participant ever experienced food poisoning 

▪ perception of how common it is for people to get food poisoning because of the way 

food is prepared at home. 

▪ view on risk of getting food poisoning 

▪ thawing practices 

– method used 

– days before cooking or discarding thawed meat if not prepared the same day 

2-11 
Meal Preparation Experiment Related to Thermometer Use 

▪ storing leftovers 

– types of containers used to store large quantity of leftovers, such as soup 

– whether leftovers are stored immediately or allowed to cool 

– days before discarding leftovers 

In addition, we coded the following variables for the treatment group to describe their 

response to the thermometer video (yes/no) and the reasons for their response (coding 

categories developed): 

▪ Did the video influence your actions in the kitchen today? 

▪ Do you think the video will influence how you cook at home in the future? 

▪ Did you relate to the people or situations in the video? 

We tabulated the responses for the treatment and control groups and conducted statistical 

testing to test for differences between the two groups. 

2-12 
 

3. Results 

This section describes the characteristics of the study sample and presents the results of the 

meal preparation experiment for thermometer use, handwashing compliance, and crosscontamination. Additionally, we provide information on self-reported usual practices for 

thawing and storing leftovers based on responses to the post-observation interviews. When 

available, the results from the current study are compared with results from national 

surveys and the published literature. 

3.1 Sample Characteristics 

Of the 383 participants in the study sample, 66% were White and 86% were non-Hispanic. 

Participants represented a variety of ages with 35% in the 18 to 34 age category, 40% in 

the 35 to 54 age category, and 25% in the 55 or older age category. Fifty percent of 

participants had at least a 4-year college degree, and 46% had at least one child living in 

the household (≤17 years). About 34% of participants had at least one individual in the

household at risk for foodborne illness (i.e., adult aged 60 years or older; pregnant woman; 

child aged 5 years or younger; or individual diagnosed with diabetes, kidney disease, or 

another condition that weakens the immune system) (see Table 3-1). Section 2 compared 

the study sample with the most recent Census data. Although there are some differences in 

the distribution for age, education, and presence of a child in the household, the study 

sample is still diverse regarding the demographic characteristics of interest. 

When comparing participants in the treatment and control groups, the two groups were 

similar in terms of ethnicity, age, education, and presence of a child in the household. The 

two groups were significantly different for the distribution of race (p = .05); the control 

group had a larger percentage of White participants (71 vs. 61%) and a smaller percentage 

of Black participants (26 vs. 35%) compared with the treatment group. In addition, 

participants in the control group (40%) were significantly more likely than participants in 

the treatment group (27%) to have at least one individual in the household at risk for 

foodborne illness (p = .04). 

Table 3-1 also provides information on participants’ experience and perceptions regarding 

foodborne illness, as reported in the post-observation interviews. These are factors that 

may influence participants’ food safety behaviors. We saw no significant differences between 

responses to these questions for the treatment and control group participants. We 

summarize the responses to these questions below and compare them with results from the 

2016 Food and Drug Administration (FDA) Food Safety Survey, a national telephone survey 

of 4,169 adults (18 years or older) (Lando et al., 2016). 

Many participants in the study sample had experience with food poisoning; 34% reported 

they have personally had food poisoning, and 55% reported a family member has had food 

3-1 
Meal Preparation Experiment Related to Thermometer Use 

poisoning.6 Participants’ responses suggest that they have some concerns about food 

safety. On a scale of 1 to 7, with “1” being not at all concerned, “4” being neutral, and “7” 

being extremely concerned, 68% of participants had concerns (response of 5, 6, or 7) 

“about bacteria or viruses on or inside the food [they] cook” (mean value = 5.1). About 

66% of participants reported that it is “very” or “somewhat common” for people in the 

United States to get food poisoning because of the way food is prepared in the home, and 

33% reported that it is “not very common.” Comparing these results with those from the 

2016 Food Safety Survey, 12% of respondents to the national survey believed that it is 

“very common,” 33% believed it is “somewhat common,” and 53% believed it is “not very 

common.” Thus, the study sample appears to be more concerned about food safety than the 

study sample for the national survey. 

Almost half of participants (46%) shared the view “All types of people have about the same 

risk of getting food poisoning” versus 28% of participants who shared the view “Certain 

types of people have a higher risk of getting food poisoning.” One-fourth of participants 

(25%) shared the view “It depends; certain types of people are at higher risk for some 

types of food poisoning.” Comparing these results with those from the 2016 Food Safety 

Survey, 49% of respondents to the national survey shared the view “All types of people 

have about the same risk of getting food poisoning,” and 48% of respondents shared the 

view “Certain types of people have a higher risk of getting food poisoning.” Only 1% of 

respondents agreed with the statement “It depends; certain types of people are at higher 

risk for some types of food poisoning.” Thus, the study sample appears to have different 

views about the risk of getting foodborne illness than the study sample for the national 

survey. 

Table 3-1. Sample Characteristics 

All 

Participants Control Treatment 

Characteristic (n = 383) (n = 201) (n = 182) p valuea 

Race .05 

Caucasian or White 66% (253) 71% (142) 61% (111) 

Black or African American 30% (117) 26% (54) 35% (63) 

Other raceb 3% (13) 3% (5) 4% (8) 

Ethnicity .97 

Not Hispanic or Latino 86% (330) 86% (173) 86% (157) 

Hispanic or Latino 

(continued) 

6 Participants were asked the following questions: “Have you ever had food poisoning?” and “Has a 

family member ever had food poisoning?” Information was not collected on whether the person was 

diagnosed with food poisoning by a health care professional. 

3-2 
Section 3 — Results 

Table 3-1. Sample Characteristics (continued) 

All 

Participants Control Treatment 

Characteristic (n = 383) (n = 201) (n = 182) p valuea 

Age .78 

18–34 35% (134) 36% (71) 34% (61) 

35–54 40% (154) 37% (73) 44% (81) 

55 or older 25% (95) 28% (55) 22% (40) 

Education .49 

Less than high school or 24% (93) 25% (49) 24% (44) 

high school diploma/GEDc 

Some college 26% (99) 23% (47) 29% (52) 

Bachelor’s degree 31% (119) 33% (65) 30% (54) 

Graduate or professional 19% (72) 20% (40) 17% (32) 

degree 

Have child 17 or younger 46% (176) 46% (91) 46% (85) .98 

living in household 

Have at-risk individual living 

in householdd 

34% (130) 40% (80) 27% (50) .04 

Participant has had 54% (203) 51% (101) 56% (101) .20 

foodborne illness (selfreported) 

Participant’s family member 55% (208) 57% (113) 53% (95) .45 

has had foodborne illness 

(self-reported) 

Participant’s level of concern 

about food safetye 

Mean value 5.1 5.0 5.2 .33 

1–3 (Not concerned) 11% (42) 10% (20) 12% (22) 

4 (Neutral) 21% (79) 18% (35) 25% (44) 

5–7 (concerned) 68% (257) 72% (144) 63% (113) 

Participant’s perception of .87 

how common it is for people 

to get food poisoning 

because of the way food is 

prepared at homef 

Very common 17% (66) 17% (34) 18% (32) 

Somewhat common 49% (185) 50% (100) 47% (85) 

Not very common 33% (127) 33% (65) 35% (62) 

(continued) 

3-3 
Meal Preparation Experiment Related to Thermometer Use 

Table 3-1. Sample Characteristics (continued) 

All 

Characteristic 

Participants 

(n = 383) 

Control 

(n = 201) 

Treatment 

(n = 182) p valuea 

Participant’s view on risk of 

getting food poisoningg 

.81 

Certain types of people 

have a higher risk of 

getting food poisoning 

28% (105) 30% (59) 26% (46) 

It depends; certain types 

of people are at higher 

risk for some types of 

food poisoning 

25% (95) 23% (46) 27% (49) 

All types of people have 

about the same risk of 

46% (173) 45% (89) 47% (84) 

getting food poisoning 

Don’t know 1% (5) 3% (5) 0% (0) 

a We calculated p value significance testing using a chi-squared test for dichotomous variables and 

repeated measures of analysis of variance (i.e., ANOVA) for continuous variables for the difference 

between the control and treatment groups for each characteristic. 

b Other race includes American Indian or Alaska Native, Asian, Native Hawaiian or Other Pacific 

Islander, and two or more races. 

c Toward the end of data collection, we revised the screening questionnaire to include people with 

technical or vocational training in this category. 

d At-risk populations are people who are 60 years of age or older, children 5 years of age or younger, 

pregnant women, people diagnosed with diabetes or kidney disease, and people diagnosed with a 

condition that weakens the immune system. 

e Participants were asked the following question in the post-observation interview: “How concerned are 

you about bacteria or viruses on or inside the food you cook?” 

f Participants were asked the following question in the post-observation interview: “How common do 

you think it is for people in the United States to get food poisoning because of the way food is 

prepared in their home?” 

g Participants were asked the following question in the post-observation interview: “Of the following 

three statements, which one is closer to your view ...?” 

Sources: 2017 meal preparation experiment—data are from the screening questionnaire or postobservation interview (as noted in footnotes). For the post-observation interviews, useable data are 

not available for 5 participants (n = 199 control and 179 treatment). 

3.2 Intervention-Specific Results: Thermometer Use 

The first iteration of the meal preparation experiment focused on participants’ food 

thermometer use and cooking to the safe endpoint temperature when preparing ground 

turkey patties. Participants were asked to prepare two turkey patties, a chef’s salad, and a 

salad dressing. 

3-4 
The lmponance of Cooking to a Sare Internal Temperature and How to Use a Food Thermometer 

., ........ StlN4 

The lmponance of Cooking to a Safe Internal Temperature and How to Use a Food Thermometer 

59,804views 1, 18 .,I 6 ,+ SHARE r+ 

Section 3 — Results 

At the time of 

recruitment, 61% of 

control group and 63% of 

treatment group 

participants reported 

owning a food 

thermometer (see Table 

3-2). These results are 

generally consistent with 

the 2016 Food Safety 

Survey (Lando et al., 

2016), in which 67% of 

consumers reported 

owning a food 

thermometer. 

Overall thermometer use 

data show that of the 

383 participants 206 

(54%) used a 

thermometer to measure 

Screenshots from 

USDA Video on 

Using a Food 

Thermometer 

Source: U.S. 

Department of 

Agriculture. 

(2015). The 

importance of 

cooking to a safe 

internal 

temperature and 

how to use a 

food 

thermometer 

[video]. 

Retrieved from 

https://www.you 

tube.com/watch? 

v=-2KkV2yFiN0 

the temperature of at least one of the ground turkey patties.7 The control group used a 

thermometer 34% of the time, while participants who were exposed to the video used a 

thermometer to check doneness 75% of the time (significant at p < .001) (see Table 3-2). 

Thus, individuals exposed to the video on thermometer use were more than 2 times likely to 

use a thermometer when cooking ground turkey patties than individuals who were not 

shown the video. The control group’s thermometer usage was higher than the 2016 Food 

Safety Survey (Lando et al., 2016) self-reported behaviors—10% for hamburgers and 19% 

for chicken parts—but in line with the International Food Information Council’s (2015) Food 

& Health Survey 2015 where more than 30% of consumers reported always using a food 

thermometer when cooking poultry. 

Attempts to use a food thermometer were further analyzed to demonstrate that 42% of 

attempts (23% control, 52% treatment, significant at p < .001) were in the correct location 

of the patty; that is, the thermometer was inserted into the side of the turkey patty to reach 

the center to seek the coldest spot. Previous studies have mainly focused on recording just 

thermometer attempts (not placement), and, in some cases, the final cook temperature was 

7 Twenty video files were corrupted and could not be recovered. The results for these participants are 

based on information recorded on the trigger sheets. 

3-5 
Meal Preparation Experiment Related to Thermometer Use 

measured after some elapsed time (Phang & Bruhn, 2011); therefore, we are unable to 

compare correct thermometer use with previous work. 

Table 3-2. Rate of Thermometer Use 

Self-reported thermometer 

ownership 

Participants using a thermometer 

Number of total attempts (multiple 

attempts per observation 

counted)b 

Correct placement among total 

attempts (inserted in the side of 

the patty, to the center)c 

Control Treatment 

(n = 201) (n = 182) p valuea 

61.2% (123) 63.2% (115) .57 

34.3% (69) 75.3% (137) <.001 

168 322 <.001 

22.6% (38) 52.2% (168) <.001 

a We calculated p value significance testing using a chi-squared test for dichotomous variables and 

repeated measures of analysis of variance (i.e., ANOVA) for continuous variables for the difference 

between the control and treatment groups for each outcome. 

b “Attempt” is defined as a participant using a food thermometer to check the doneness of one or both 

turkey patties. 

c “Correct placement” is defined as a participant inserting the thermometer into the side of the turkey 

patty to reach the center and held for at least 5 seconds before the temperature is determined.. 

Source: 2017 meal preparation experiment—screener (self-reported thermometer use) and coding of 

food preparation. 

The portion of the intervention video that is specific to hamburger patties demonstrated how 

to insert the thermometer from the side and provided the message to measure the 

temperature of each patty. Figure 3-1 is a diagram of a turkey patty with a heat map 

indicating thermometer placement for the control and treatment group participants. The 

red-colored dots indicate points of thermometer insertion. The brown area represents the 

top of the turkey patty, and the blue halo represents the side profile of the patty, meaning 

that a red point in the blue halo indicates that a participant inserted the thermometer 

through the side of the patty. Comparing the two heat maps indicates the treatment group 

participants were more likely than the control group participants to insert the thermometer 

into the side of the patty, which is the recommended practice. 

3-6 
D D 

D D 

Section 3 — Results 

Figure 3–1. Turkey Patty with Heat Maps Showing Thermometer Placement by 

Group 

North

East

South

West

Control 

North

East

South

West

Treatment 

Note: “North” is the part of the pan that is farthest from the participant. The red dots indicate the 

placement of thermometer insertion. The brown area represents the top of the turkey patty; the 

blue halo represents the side profile of the turkey patty. Number of participants who used a food 

thermometer = 69 control group and 137 treatment group. 

Source: 2017 meal preparation experiment—coding of food preparation. 

3-7 
Meal Preparation Experiment Related to Thermometer Use 

Treatment group participants were Table 3-3. Number of Patties for Which 

Temperature Was Checked significantly more likely than control Among Participants Who Used 

group participants to check the a Food Thermometer 

temperature of both patties (82 vs. Control Treatment 

73%, p < .001), which is the (n = 60) (n = 128) p valuea 

recommended practice (see Table 3-3). One patty 26.7% 18.0% .067 

(16) (23) Two factors that can affect even 

Two patties 73.3% 82.0% <.001 heating are the state of the product (44) (105) before cooking (e.g., frozen, 

refrigerated, or room temperature) and a We calculated p value significance testing using a 

chi-squared test for the difference between the the amount of times during cooking the control and treatment groups for each outcome. 

product is turned over (i.e., flipped) Notes: N = 206 for thermometer; N = 188 

(Berry and Bigner-George (2001); Gill, (obtainable number for analysis). The number of 

patties checked was undetermined for 18 Yang, Uttaro, Badoni, & Liu, 2013; observations because the videos needed to make 

Luchansky et al., 2013). The side of the this determination were corrupted. 

hamburger that is farthest away from Source: 2017 meal preparation experiment—coding 

of food preparation. the heat of the grill or the bottom of a 

frying pan can differ by as much as 

80°F. Yang et al. (2017) and Luchansky et al. (2013) demonstrated the impact of flipping 

meat while cooking, showing that more than three flips with nonintact beef result in the 

highest reduction of E. coli O157:H7. Research has shown that there are substantial 

differences between heating surface and product endpoint temperatures because the center 

of the hamburger is not heated directly by the pan temperature but rather by the steam– 

water interface temperature, Table 3-4. Number of Flips per Patty (two patties which is inside the surface of per participant) 

the hamburger (Juneja, Control Treatment 

Snyder, Williams, & Marmer, (n = 374 (n = 326 p 

1997). Berry and Bigner- patties) patties) valuea 

George (2001) demonstrated No flips (used clamshell 3.2% (12) 2.8% (9) 

grill or baked in oven) substantial temperature One flip 16.3% (61) 15.3% (50) 

variability within patties Two flips 17.1% (64) 20.2% (66) 

because of the considerable Three or more flips 63.4% (237) 61.7% (201) 

temperature variability that Mean number of flips 2.4 2.4 .958 

can exist within patties at the Total 100.0% 100.0% 

end of cooking. As shown in a We calculated p value significance testing using a t test for the 

Table 3-4, about one-third of difference between the control and treatment groups for the 

mean number of flips per patty. participants in the treatment 

N = 700 patties (obtainable number for analysis). and control groups flipped the Source: 2017 meal preparation experiment—coding of food 

patties fewer than three flips. preparation. 

3-8 
Section 3 — Results 

Each time a participant used a thermometer to check for doneness, a data logger recorded 

the temperature of the patty every second to determine whether it reached a safe endpoint 

temperature, either 165°F instantaneously or a time–temperature relationship that would 

result in the same level of reduction of potentially harmful bacteria (e.g., 164°F for 11.2 

seconds). We determined safe endpoint time–temperature combinations using USDA FSIS‘s 

Appendix A: Times for given temperature and fat level of turkey needed to obtain 7-log 

lethality of Salmonella (USDA, FSIS, 2017). Among participants who used a thermometer 

and for whom a 

Table 3-5. Time–Temperature Combinations for 

time and temperature 

temperature was Turkey Patties Deemed Safe 

available, 67% of patties 

(54% control, 73% 

treatment, significant at 

p < .008) reached an 

instant 165°F, which 

Instant 165°F 

Time–temperature 

combinationb 

Control 

(n = 44) 

54% (24) 

Treatment 

(n = 91) 

73% (66) 

p valuea 

.008 

represents the final 164°F for 11.2 seconds 0 0 — 

thermometer reading for 163°F for 13.8 seconds 0 0 — 

the turkey patty (see 162°F for 17 seconds 0 0 — 

Table 3-5); no patties 

reached a safe 

161°F for 21 seconds 0 0 — 

temperature for other 160°F for 25.8 seconds 

155°F for 72 seconds 

0 

0 

0 

0 

— 

— 

a We calculated p value significance testing using a chi-squared test combinations. Thus, for the difference between the control and treatment groups. patties cooked by the b Time–temperature combinations are from USDA FSIS, Appendix A: 

treatment group Times for given temperature and fat level of turkey needed to 

obtain 7-log lethality of Salmonella (USDA, FSIS, 2017). participants were 

Notes: N = 206 for thermometer use; N = 135 (obtainable number). significantly more likely Data are not available for 71 participants because participants 

to reach an instant 165°F submerged the data logger (25 control and 46 treatment 

recordings unrecoverable). compared with the Source: 2017 meal preparation experiment—data logger. control group 

participants. Although there are differences between handling beef and poultry products, 

these results are comparable to Phang and Bruhn’s (2011) results, which showed that for 

83% of participants who were asked to prepare ground beef hamburger patties at home, 

the burger temperature was above the recommended safe temperature threshold. About 

20% (27 out of 137) of the endpoint temperature recordings for the current study were 

below 150°F; the lowest recorded endpoint temperature was 65°F (see Table 3-6). It is 

important to note that these participants could have continued to cook the patties and used 

a subjective measure (such as cutting) to determine doneness. Additional analysis is being 

conducted to determine whether these 27 participants continued to cook the patties or 

considered the patties to be done after checking the temperature. 

3-9 
Meal Preparation Experiment Related to Thermometer Use 

Table 3-6. Distribution of Endpoint Temperatures Among Participants Who Used 

a Food Thermometer 

Degrees Control (n = 44) Treatment (n = 91) 

165+ 54% (24) 73% (66) 

160–164.9 11% (5) 3% (3) 

155–155.9 2% (1) 4% (4) 

150–154.9 5% (2) 3% (3) 

145–149.9 7% (3) 1% (1) 

140–144.9 0 0 

135–140 0 0 

130–135 2% (1) 1% (1) 

125–130 2% (1) 2% (2) 

120–125 0 0 

115–120 0 1% (1) 

110–115 0 0 

105–110 0 0 

100–105 0 0 

95–100 0 0 

90–95 2% (1) 1% (1) 

85–90 0 0 

80–85 2% (1) 2% (2) 

75–80 5% (2) 2% (2) 

70–75 5% (2) 3% (3) 

65–70 2% (1) 2% (2) 

60–65 0 0 

Total 100% (44) 100% (91) 

Notes: N = 206 for thermometer use, N = 135 (obtainable number). Data are not available for 71 

participants because participants submerged the data logger (25 control and 46 treatment 

recordings unrecoverable). It is possible that participants could have continued to cook the patties 

after checking the temperature and used a subjective measure (such as cutting) to determine 

doneness. 

Source: 2017 meal preparation experiment—data logger. 

A total of 45% (n = 172) of participants used another method to determine doneness 

besides using a thermometer. Among these participants, 46% of participants in the control 

group and 29% of participants in the treatment group relied on the firmness/texture of the 

patty to determine if the patty was done (see Table 3-7). Twenty-five percent of 

participants in the control group and 42% of participants in the treatment group were 

3-10 
Section 3 — Results 

observed using more than one method—firmness and color of the patty—to determine 

doneness. 

Table 3-7. Methods Used to Determine Doneness for Participants Who Did Not 

Use a Food Thermometer 

Method Source 

Control 

(n = 127) 

Treatment 

(n = 31) 

p 

valuea 

Only used color Self-reported: inside color 26% (33) 16% (7) .27 

Self-reported: outside color 0% (0) 7% (3) 

Observations 4% (5) 16% (5) .08 

Only used touch (firmness or Self-reported 5% (7) 5% (2) .92 

texture of burger) Observations 46% (59) 29% (9) .11 

Used more than one method Self-reported 70% (93) 71% (29) .92 

(color and touch) 

Observations 25% (32) 42% (13) .09 

Unobservable method (e.g., Observations 24% (31) 10% (3) .02 

cooking time) 

Total Self-reported/observations 100% 100% 

a We calculated p value significance testing using a chi-squared test for the difference between the 

control and treatment groups for each method. 

Notes: N = 172; N = 158 (obtainable number); data are not available for 14 participants because of 

corrupted/unrecoverable video files. The unobservable methods include participants who relied on 

cooking time and those who might have looked at the outside color (without touching the patty). 

Sources: 2017 meal preparation experiment—coding of food preparation (observed) and screening 

questionnaire data (self-reported usual behavior). 

Among participants who used a food thermometer and useable data were available (n = 

191), 38% of participants in the control group and 42% of the participants in the treatment 

group relied solely on the food thermometer (see Table 3-8). However, self-reported rates 

from the screener for thermometer use as the sole method were considerably lower: 6% for 

the control group and 5% for the treatment group. One possible explanation for this is the 

use of turkey burgers. The screener did not specifically mention turkey; rather, it asked, 

“How do you determine whether the burgers are done and ready to eat?” From the postobservation interviews, many participants mentioned feeling less comfortable determining 

doneness from color and/or texture with turkey burgers than with hamburgers made from 

ground beef. This lack of experience or comfort with cooking turkey burgers could be one 

possible reason for the higher rate of thermometer use as the sole method for determining 

doneness. The most common observed methods to determine doneness among 

thermometer users using multiple methods were thermometer use and the firmness/texture 

of the patty (70% control and 79% treatment). 

3-11 
Meal Preparation Experiment Related to Thermometer Use 

Table 3-8. Other Methods Used to Determine Doneness for Participants Who Did 

Use a Food Thermometer 

Control Treatment p 

Method Source (n = 60) (n = 131) valuea 

Only used thermometer Self-reported 6% (4) 5% (7) .87 

Observations 38% (23) 42% (55) .63 

Only used color Self-reported: inside color 22% (13) 26% (36) .35 

Self-reported: outside color 0% (0) 0% (0) 

Observations 0% (0) 0% (0) 

Only used touch (firmness or 

texture of burger) 

Self-reported 

Observations 

1% (1) 

0% (0) 

2% (3) 

0% (0) 

.26 

Used more than one method Self-reported 30% (50) 68% (97) .38 

Observations 62% (37) 58% (76) 

Method used, if more than 

one method used (from 

observations) 

Used therm. & touch 70% (26) 79% (60) .75 

Use therm. & color 3% (1) 5% (4) .53 

Use therm., touch, & 

color 

27% (10) 16% (12) .17 

Total Self-reported/observations 100% 100% 

a We calculated p value significance testing using a chi-squared test for the difference between the 

control and treatment groups for each method. 

Notes: N = 212; N = 191 (obtainable number); data are not available for 21 participants because of 

corrupted/unrecoverable video files. 

Sources: 2017 meal preparation experiment—coding of food preparation (observed) and screening 

questionnaire data (self-reported usual behavior). 

Overall, these results suggest that the intervention (USDA video on thermometer use) was 

effective in encouraging participants in the treatment group to use a thermometer and to 

place it in the correct location of the patty; among the temperatures we were able to 

measure when a thermometer was used, the patty was cooked to a safe temperature 67% 

of the time (treatment = 73% correct and control = 54% correct (p < .008). 

3.3 Handwashing Compliance 

Inadequate handwashing has been identified as a contributing factor to foodborne illness, 

especially when preparing raw meat and poultry. Hands can become vectors that move 

pathogens around sites for foodborne pathogens found in raw meat and poultry and that 

contribute to home-acquired foodborne illnesses. Frequency and level of contamination of 

hands have not been well studied. 

The USDA video on thermometer use does not provide information on the need to wash 

hands before and during cooking and or on proper handwashing procedures. However, we 

3-12 
Section 3 — Results 

measured handwashing compliance in this study because FSIS needs information on 

consumer adherence to the recommended practices for each study year for all four key food 

safety messages (clean, separate, cook, and chill). Also, we wanted to assess whether a 

food safety video on thermometer use influences other food safety behaviors. 

The total handwashing attempts required per observation are determined during the coding 

for each observation. For example, a handwashing event is required for each of the 

following instances: 

▪ before touching RTE foods at the onset of food preparation 

▪ anytime between touching raw meat or packaging and then touching a nonmeat item 

▪ after touching another person or self 

▪ after touching cell phone 

▪ after multitasking (chores) 

▪ after touching contaminated (post-meal) trash or trash can 

The total number of attempts per observation is the number of times a participant washed 

their hands. Each handwashing event was coded as adequate or inadequate based on the 

criteria set by the Center for Disease Control and Prevention (CDC): wet hands with water; 

rub hands with soap for at least 20 seconds; rinse hands with water; and dry hands using a 

clean, one-use towel. For example, participant 001T was required to wash her hands nine 

times but attempted only two times. Of these two times, neither was coded as successful 

because she did not scrub her hands for a total of 20 seconds. 

We observed 2,249 cases in which a handwashing event was required to control pathogens; 

of these, handwashing was attempted 31% of the time (see Table 3-9). Among 

handwashing events attempted, only 4% of attempts contained all steps of a correct 

handwashing event. As shown in Table 3-10, the most common reason for unsuccessful 

handwashing was not rubbing hands with soap for at least 20 seconds (76% in the control 

group and 83% in the treatment group), followed by not wetting hands with water (40% in 

the control group and 44% in the treatment group). Nearly a third of all attempts did not 

include proper drying. Drying hands using a clean or one-use towel is an important step in 

handwashing because it can physically remove microbes and contaminants from hands, 

resulting in up to a 1 log reduction (Huang, Ma, & Stack, 2012). There were no significant 

differences between the treatment and control groups. 

3-13 
Meal Preparation Experiment Related to Thermometer Use 

Table 3-9. Handwashing Compliance 

Control Treatment 

(n = 185) (n = 165) p valuea 

Handwashing event required 1,195 1,054 .429 

Attemptsb 30.5% (365) 32.5% (343) .175 

Successful attemptsc,d 0.8% (10) 1.5% (16) .066 

Before meal preparation 100% (10) 100% (16) 

After touching raw turkey (0%) 0 (0%) 0 

Undetermined 1 2 

Missing 8 12 

a We calculated p value significance testing using a chi-squared test for the difference between the 

control and treatment groups for handwashing compliance. b “Attempt” is defined as any time that a participant appeared to clean their hands; the attempt could 

be adequate or inadequate. c A successful attempt is defined as a participant meeting all the criteria set by CDC: wet hands with 

water; rub hands with soap for at least 20 seconds; rinse hands with water; and dry hands using a 

clean, one-use towel. d All successful attempts at handwashing occurred before beginning meal preparation. No successful 

attempts occurred after directly handling raw turkey. 

Notes: Number of events in which handwashing was required = 1,195 control group and 1,054 

treatment group. Number of observations coded: control = 185 and treatment = 165. Data for the 

remaining participant observations are not recoverable because of damaged/corrupted/incomplete 

video files. 

Source: 2017 meal preparation experiment—coding of food preparation. 

Table 3-10. Reasons for 0-Unsuccessful Handwashing Attempts 

Control Treatment 

Total Total 

Reasona 

Attempts 

Needed 

(n = 1,170) 

Unsuccessful 

Attempts 

(n = 355) 

Attempts 

Needed 

(n = 1,049) 

Unsuccessful 

Attempts 

(n = 327) 

p 

valueb 

Did not wet hands with 

water 

39.7% (141) 44.3% (145) .11 

Did not use soap 23.9% (85) 18.0% (59) .36 

Did not rub hands with soap 

for at least 20 seconds 

75.8% (269) 82.6% (270) .39 

Did not rinse hands with 

water 

0.6% (2) 0.9% (3) .31 

Did not dry hands 13.0% (46) 10.1% (33) .77 

Dried hands with surface 

other than clean, one-use 

towel (e.g., wiped hands on 

clothing or used previously 

used towel) 

16.3% (58) 23.2% (76) .67 

(continued) 

3-14 
Section 3 — Results 

Table 3-10. Reasons for Unsuccessful Handwashing Attempts (continued) 

Control Treatment 

Reasona 

Attempts 

Needed 

(n = 1,170) 

Total 

Unsuccessful 

Attempts 

(n = 355) 

Attempts 

Needed 

(n = 1,049) 

Total 

Unsuccessful 

Attempts 

(n = 327) 

p 

valueb 

Undetermined 1 2 

Missing 8 12 

a There may be multiple reasons for a handwashing event to be unsuccessful, so the percentages sum 

to more than 100%. b We calculated p value significance testing using a chi-squared test for the difference between the 

control and treatment groups for each reason. 

Notes: Number of participant observations coded = 185 control and 165 treatment. Number of events 

in which handwashing was required among coded observations = 1,170 control group and 1,049 

treatment group. Number of unsuccessful handwashing attempts among coded observations = 355 

control group and 327 treatment group. Data for the remaining participant observations are not 

recoverable because of damaged/corrupted/incomplete video files. 

Source: 2017 meal preparation experiment—coding of food preparation. 

3.4 Cross-Contamination and Microbiological Analysis 

We also analyzed the spread of MS2 from the spiked turkey patties to various surfaces and 

RTE food products. Lack of or failed handwashing attempts can spread pathogens to high 

touch surfaces through contact of contaminated hands to surfaces and foods. 

Campylobacter and Salmonella, pathogens found in poultry products, have been shown to 

be viable on food contact surfaces for 4 to 32 hours respectively (De Cesare, Sheldon, 

Smith, & Jaykus, 2003) posing a potential health risk in the home if contaminated surfaces 

are not adequately cleaned and sanitized. 

We used the microbiological data to identify both the direct and indirect cross-contamination 

events that occurred during the meal preparation experiment. Direct cross-contamination is 

defined as when raw meat or raw meat packaging (in this case ground turkey) comes into 

direct contact with a RTE food or a food handling surface or utensil and the area is not 

cleaned and sanitized after contact. Indirect cross-contamination is when utensils, surfaces, 

and/or hands make contact with a contaminant and then are not cleaned and/or sanitized 

adequately before the next use, any time between touching raw meat or packaging and 

then touching a nonmeat item, touching a mobile device, or touching trash. For the draft 

report, we analyzed the data for mobile devices (if used), the refrigerator handle, spice 

containers, and the faucet handle. Table 3-11 shows the prevalence and level of 

contamination for these four sites, as well as the prevalence and level of contamination in 

the salad lettuce. This section describes the results and whether differences between the 

treatment and control groups are statistically significant. 

3-15 
Table 3-11. Prevalence of MS2 Contamination and Level of Contamination for Four Locations in the Kitchen and 

Salad Lettuce 

Location All Participants Control Treatment p valuea 

Refrigerator 

handle 

Prevalence contaminated % (n) 

Level of contamination ± SD, log genome 

copiesb/handle (n) 

8.09% (372) 

5.50 ± 0.37 (30) 

10.55% (199) 

5.47 ± 0.38 (21) 

5.23% (172) 

5.51± 0.34 (9) 

.0615 

Spice 

containers 

Prevalence contaminated, % (n) 

Level of contamination ± SD, log genome 

copies/bottle (n) 

48.79% (372) 

6.18 ± 0.82 (181) 

48.24% (199) 

6.28 ± 0.83 (96) 

49.42% (172) 

6.07 ± 0.78 (85) 

.8139 

Faucet handle Prevalence contaminated, % (n) 12.13% (372) 11.06% (199) 13.37% (172) .4939 

Level of contamination ± SD, log genome 

copies/bottle (n) 

5.47 ± 0.52 (45) 5.51 ± 0.47 (22) 5.44 ± 0.56 (23) 

Mobile device 

(if used) 

Prevalence contaminated, % (n) 

Level of contamination ± SD, log genome 

copies/device (n) 

7.79% (78) 

5.73 ± 0.79 (6) 

5.71% (35) 

5.54 ± 1.51 (2) 

9.30% (43) 

6.11 ± 0.39 (4) 

.5565 

Salad lettuce Prevalence contaminated (total)c, d % (n) 5.96% (367) 5.05% (199) 6.43% (168) .5688 

Prevalence contaminatede,d % (n) 9.90% (222) 9.17% (109) 9.73% (113) .8869 

Level of contamination (SD), log genome 

copies/18–25g (n) 

5.52 ± 0.45 (22) 5.64 ± 0.74 (10) 5.46 ± 0.44 (11) 

Meal Preparation Experiment Related to Thermometer Use 

Notes: Microbiological samples are available for 369 of the 383 participants. Samples are not available for 10 participants because toward the 

end of data collection there was insufficient daily lab capacity to process their samples. The control sample used to validate cleaning was 

positive in one sample and was excluded from all microbiological analyses. The microbiological analysis for three participants needs to be 

repeated because of inhibition in the PCR. 

A positive result was one within 5 logs of the total inoculum (approximately log 10). 

We would not expect contamination levels of pathogens in USDA-regulated food products to exceed log 5, in step with data-supported 

assumptions found in 9 CFR Parts 301, 317, 318, 320, and 381. 

(n) = number of samples used in the analysis; SD = standard deviation. 

a We calculated p value significance testing using a chi-squared test for prevalence and repeated measures of analysis of variance (i.e., 

ANOVA) for level of contamination for the difference between the control and treatment groups. 

(continued) 

3-16 
Table 3-11. Prevalence of MS2 Contamination and Level of Contamination for Four Locations in the Kitchen and 

Salad Lettuce (continued) 

b A genome copy is the RT-qPCR equivalent of one bacteriophage particle, as calculated using a standard curve generated from a sample with 

known genome copy concentration as described in Appendix F. 

c Results include the salad lettuce samples that were not tested (n = 222) because these participants prepared the salad before preparing the 

turkey patties; thus, the samples are assumed to be negative because there was no opportunity for cross-contamination (i.e., contact with 

raw turkey or its packaging). These results are more representative of overall prevalence of salad lettuce contamination. 

d Three samples were unusable because the lettuce from the salad and the lettuce from the burger garnish were combined, and lettuce was 

not taken for one observation; these participants were excluded from the lettuce analysis but included in the surface analysis. 

e Results are for the salad lettuce samples that were actually tested, that is, the salad lettuce that potentially could have been contaminated 

because the participant prepared the salad after preparing the turkey patties. 

Source: 2017 meal preparation experiment—microbiological samples. 

Section 3 — 

3

Results 

-17 
Meal Preparation Experiment Related to Thermometer Use 

The spice containers were the most frequently contaminated sample of those analyzed to 

date, with approximately 50% of participants contaminating these surfaces (independent of 

control/treatment). While coding for behaviors leading up to their contamination has not yet 

been conducted (to be provided in report supplement with final microbiological results in 

July 2018), it is likely that participants handled raw turkey patties immediately before 

picking up spice containers to season the patties. Similarly, for the faucet handle, which was 

found to be contaminated approximately 12% of the time (independent of 

control/treatment), it is likely that participants contaminated this surface in an attempt to 

perform a handwashing event following the contamination of hands by turkey patties or 

their packaging. Interestingly, the refrigerator handle was shown to be contaminated less 

frequently in the treatment group (approximately 5% of the time) compared with the 

control group (approximately 11% of the time); however, this difference was not significant 

(p = .0615). It is possible the treatment group collected all needed ingredients for the meal 

preparation in fewer trips to the refrigerator than the control group, resulting in fewer touch 

events; we will confirm this hypothesis in the final microbiological report supplement to be 

delivered in July 2018. 

A total of 78 participants used their mobile device at some point after handling turkey 

packaging, and six devices were found to be contaminated. Table 3-12 shows the sequences 

of contacts leading to contamination based on the prevalence and level of contamination 

among the six positive samples for mobile devices. In four out of the six cases, there was a 

direct contamination event where the contaminated patty/and or packaging was touched 

directly to the mobile device. In the other two cases, a failed handwashing event led to the 

contamination. As the entire surface area of the mobile devices were swabbed, and they 

varied in surface area, no conclusions can be drawn from the level of contamination on the 

devices. However, these results show the need for improving handwashing practices in the 

home, studies to determine how long pathogens remain viable on mobile devices and their 

cases to determine potential public health risk, and data on how potentially contaminated 

mobile devices are shared in the home or used by individuals at higher risk (e.g., young 

children) during meal preparation, including for viewing and following recipe instructions. 

3-18 
Section 3 — Results 

Table 3-12. Sequences of Contact Leading to Contamination Based on Prevalence 

and Level of Contamination for Mobile Phones (n = 6, out of 77) 

Level of Contamination 

Genome Copies/Mobile 

Positive Mobile Device n Device 

Turkey patty → Mobile device 2 5.58 ± 0.02 

Turkey patty packaging → Mobile device 2 5.51 ± 0.66 

Turkey patty → Failed handwashing attempt → Another 1 7.17 

surface → Mobile device 

Turkey patty → Failed handwashing attempt → Another 1 5.03 

surface → Another surface → Mobile device 

Source: 2017 meal preparation experiment—coding of food preparation. 

Discretionary samples of cloth towels were collected for some participants, and 

microbiological analysis is forthcoming. Kitchen towels have been shown to be a harborage 

site for surrogates in previous studies. Both paper towels and cloth towels were available to 

participants in this study, and participants opted to use paper towels over cloth towels most 

of the time. Discrepancies between the current study and the observation meal preparation 

experiment conducted by Sneed and colleagues (2015) may be due to different surrogates, 

differences in the tasks that were required of participants, and sample demographic 

differences. 

Salad lettuce samples were only taken if the participant handled the turkey patties in any 

way before preparing the salad; if the salad was prepared before touching the turkey, the 

salad was assumed to be negative and the garnish lettuce was sampled instead. The salad 

lettuce was contaminated 6% of the time, including all unsampled salad lettuce assumed to 

have 0% contamination and 10% from those samples actually taken with no significant 

difference between the treatment and control groups in either case. The garnish lettuce 

used for the burger was not fully analyzed because of the small sample obtained (less than 

20 g); a high proportion of positives is unlikely. The lack of difference between the 

treatment and control groups indicates that safe thermometer behavior does not necessarily 

influence cross-contamination behaviors. Thus, separate messaging is likely needed to 

change such behaviors. 

The relatively low rate of contamination of salad lettuce (6%) indicates that crosscontamination was not necessarily frequent but did occur with some regularity. This finding 

suggests an increased risk of foodborne disease associated with these cross-contamination 

events. However, the very low concentrations of the surrogate that occurred on salad due to 

cross-contamination would reduce that risk to some extent. Consequently, the role of crosscontamination alone in elevating foodborne disease risk at the consumer level remains 

uncharacterized, until further risk assessment work is done. It should be noted that crosscontamination has often been highlighted in previous studies attempting to characterize 

3-19 
Meal Preparation Experiment Related to Thermometer Use 

consumer behaviors. Preliminary, although as yet incomplete, coding of the observations 

suggests that a missed or failed handwashing attempt was part of the sequence that led to 

cross-contamination of the salad lettuce. Direct contamination of the salad lettuce by the 

turkey patties seems much less likely to be the contaminant source, in contrast to 

contamination of the spice containers, which was likely direct. 

3.5 Self-Reported Usual Practices for Thawing and Storing 

Leftovers 

The post-observation interviews collected information on behaviors that we were unable to 

observe regarding thawing frozen meat or poultry and storing leftovers (see Table 3-13). As 

previously noted for handwashing compliance, although these behaviors are not discussed 

in the intervention video, the project is designed so that information is collected on the key 

food safety messages (clean, separate, cook, and chill) in each iteration of the meal 

preparation experiment. As discussed below, responses were similar for the treatment and 

control groups. 

About 79% of participants in the treatment group and 81% of participants in the control 

group reported they would use a USDA-recommended method (refrigerator, microwave, or 

cold water) to thaw raw meat or poultry. Thawing on the countertop and in a hot water bath 

and/or in a bowl without changing the water were methods used by some participants. One 

participant who thaws in water without changing the water noted that she normally places 

the meat in cold water before leaving for work, comes home after 8 hours, and then cooks it 

that evening, “It’s like eight hours [laughter] when I get home. Eight. I just go straight and 

cook it, so.” 

Behaviors coded as “other methods” (n = 5) included setting meat on top of a running 

clothes dryer “because it heats, it unfreeze the meat more quickly” and a dish-rack (not the 

counter) because it is “faster if you put it on so air is getting all the way around it. And I 

know I’m not supposed to but hey, I’m 67 and nobody’s gotten sick.” 

If participants thawed raw meat or poultry but were unable to cook it on the same day, 

87% of participants in the treatment group and 86% of participants in the control group 

reported they would cook or discard the meat or poultry within 2 days per USDA 

recommendations for refrigerator thawing. 

Regarding storage of leftovers (see Table 3-13), if participants cooked a large pot of soup or 

chili and had enough to eat the next day, 55% of participants in the treatment group and 

46% of participants in the control group reported they would store the leftovers in multiple 

small containers. In addition, 8% of participants in the treatment group and 12% of 

participants in the control group reported they would refrigerate the leftovers “immediately” 

per USDA recommendations, instead of letting the leftovers cool before placing them in the 

refrigerator. Information on the amount of time that participants consider to be “immediate” 

3-20 
Section 3 — Results 

is not available. The 2016 FDA Food Safety Survey reports that 19% of respondents would 

refrigerate similar leftovers immediately and 76% of respondents would refrigerate after 

letting the soup or chili cool to room temperature. Finally, about 70% of both treatment and 

control group participants reported they would store leftovers in the refrigerator or discard 

them within 4 days. Some participants noted they use different discard times for different 

foods and meats: 

▪ “Depending on the food, usually no more than 2 or 3 days. Yeah. Usually, I’ll try to 

eat it the next day and the day after that.” 

▪ “We have food labels that we bought at the restaurant. We give everything 2 weeks 

and things like fish get 1 week.” 

▪ “It depends on what it is. If it’s chicken, 2 days max. If it’s chili with ground beef, 

then 3 to 5 days, but not longer than that.” 

▪ “It does depend on what it is. But if we’re talking specifically soup, I would say 5 

days.” 

Table 3-13. Self-Reported Practices for Thawing and Storing Leftovers 

Control Treatment p 

(n = 200) (n = 182) valuea 

Thawing methodb .95 

Microwave 6% (12) 4% (8) 

Refrigerator 70% (141) 69% (127) 

Water in sink—use cold water and change 5% (9) 6% (11) 

water 

Water in sink—unsafe method (e.g., used hot 10% (20) 9% (16) 

water or did not change water) 

On countertop 8% (16) 10% (17) 

Other method 1% (2) 2% (3) 

Total 100% 100% 

If thawed meat or poultry but didn’t cook it the .95 

same day, number of days store in refrigerator 

before cooking or discarding itc 

Discard 10% (20) 7% (13) 

1 45% (91) 53% (97) 

2 31% (62) 27% (48) 

3 10% (20) 10% (18) 

4 1% (2) <1% (1) 

5 or more days 3% (5) 3% (5) 

Total 100% 100% 

Method of leftover storage (for large pot of soup 

or chili)d 

.92 

Place leftovers in one container 53% (106) 42% (77) 

Place leftovers in multiple small containers 46% (92) 55% (99) 

(continued) 

3-21 
Meal Preparation Experiment Related to Thermometer Use 

Table 3-13. Self-Reported Practices for Thawing and Storing Leftovers 

(continued) 

Control Treatment p 

(n = 200) (n = 182) valuea 

Method of leftover storage (for large pot of soup 

or chili)d (continued) 

.92 

Place leftovers in multiple large containers 1% (2) 3% (6) 

Total 100% 100% 

Timing of leftover storage (for large pot of soup 

or chili)d 

.97 

Let leftovers cool before placing in refrigerator 88% (176) 92% (168) 

Refrigerate leftovers immediately 12% (24) 8% (14) 

Total 100% 100% 

Length of time would store leftovers before .98 

eating or discarding them 

1 to 4 days 69% (138) 71% (129) 

5 or more days 31% (62) 29% (53) 

Total 100% 100% 

a We calculated p value significance testing using a chi-squared test for the difference between the 

control and treatment groups for each response options. 

b Participants were asked the following question: “Imagine you have meat or chicken in the freezer, 

and you plan to cook it for dinner later in the week. How would you thaw it?” 

c If participants provided a range of days (e.g., 3 to 5 days), the latest date were coded (e.g., 5). 

d Participants were asked the following question: “Imagine you just cooked a large pot of soup or chili 

so that you would have enough to eat the next day. What do you do with the leftovers?” 

Note: Interview data are not available for one participant because the interview was not conducted 

because of time constraints. 

Source: 2017 meal preparation experiment—post-observation interviews. 

3.6 Participant Response to USDA Video on Thermometer Use 

(Treatment Group Only) 

Post-observation interviews included collecting information about the participants’ response 

to the USDA video on thermometer use viewed by participants in the treatment group 

before cooking. Table 3-14 shows the results from these questions and common reasons for 

participants’ responses. 

3-22 
Section 3 — Results 

Table 3-14. Participants’ Responses to USDA Video on Thermometer Use 

Response/Reasons, % (n) 

Question Yes No 

Did the video influence your action in the kitchen today? 67% (121) 33% (60) 

Why or why not?a 

Used thermometer to check doneness of patties 61% (74) 0% (0) 

Comfortable with cooking experience and other methods of 0% (0) 8% (5) 

determining doneness 

New information about temperatures 9% (11) 0% (0) 

Learned about correct placement of thermometer 8% (10) 0% (0) 

Reinforced existing thermometer use/normally use a 4% (5) 55% (33) 

thermometer at home 

Other 7% (8) 8% (5) 

Not answered/answer not clear/answer not relevant 11% (13) 28% (17) 

Total 100% (121) 100% (60) 

Do you think the video will influence how you cook at 

home in the future? Why or why not?b 

67% (115) 33% (61) 

Used thermometer to check doneness of patties 57% (66) 3% (2) 

Comfortable with cooking experience and other methods of 0% (0) 18% (11) 

determining doneness 

New information about temperatures 12% (14) 0% (0) 

Learned about correct placement of thermometer 11% (13) 2% (1) 

Reinforced existing thermometer use/normally use a 3% (3) 40% (24) 

thermometer at home 

Other 2% (2) 8% (5) 

Not answered/answer not clear/answer not relevant 15% (17) 30% (18) 

Total 100% (115) 100% (61) 

Did you relate to the people or situations in the video? 83% (148) 17% (31) 

Why or why not?c 

Similar, believable people 16% (24) 0% (0) 

Prepare similar food 34% (51) 2% (1) 

Cooking at home for family, others 18% (26) 13% (4) 

Thermometer use 7% (10) 3% (1) 

Family size similar/participant cooks for self or one other 5% (8) 50% (15) 

person 

Other 7% (10) 20% (6) 

(continued) 

3-23 
Meal Preparation Experiment Related to Thermometer Use 

Table 3-14. Participants’ Responses to USDA Video on Thermometer Use 

(continued) 

Response/Reasons, % (n) 

Question Yes No 

Not answered/answer not clear/answer not relevant 

Total 

13% (19) 

100% (148) 

27% (8) 

100% (31) 

a Number of participants = 181. One interview was not conducted because of time constraints. 

b Number of participants = 176. Data are not available for five participants because the question was 

not presented clearly to participants. One interview was not conducted because of time constraints. 

c Number of participants = 179. One interview was not conducted because of time constraints and this 

question was not asked in two interviews that were coded for this report. 

Source: 2017 meal preparation experiment—post-observation interviews. 

Approximately two-thirds of participants responded that watching the video influenced their 

cooking behavior in the test kitchen. Of these participants, 61% reported using a 

thermometer to check the doneness of the turkey patties as a result of watching the video. 

More specifically, 9% of the participants mentioned learning about the specific safe 

temperature for poultry as a primary reason for using a thermometer in the test kitchen, 

and 8% cited learning about correct placement of the thermometer. Inserting the 

thermometer into the side of the turkey patty was new information for several participants: 

▪ “Watching that video, I would have tested the meat differently probably. I wouldn’t 

have even thought to put it through the side. I’ve always just kind of poked it in 

there in the center.” 

▪ “Don’t know if I would have known to stick the meat thermometer in the side of the 

turkey burgers. That was something I learned. I would probably just stick it in the 

center.” 

▪ “I think I was a lot more conscientious of how to place the thermometer in the 

burger. Typically, I would just stab it in there and hope it wouldn’t go all the way 

down to the bottom, but I’ve never done it flat.” 

Thirty-four percent of participants reported that the video did not influence their cooking 

behavior in the kitchen; however, 55% of these participants reported that they use a 

thermometer on a regular basis in their home kitchen, and the video simply reaffirmed this 

practice. The most frequently cited reason (8%) for not using a thermometer in the test 

kitchen was participants’ own experiences and confidence with other methods of 

determining doneness: 

▪ “I haven’t had a victim yet ... my record is good.” 

▪ “No, because I cook at home all the time, so I know what done food looks like. So 

I’m extra-cautious, not because of me, but for my child.” 

3-24 
Section 3 — Results 

About 67% of participants responded that the thermometer video will influence future 

cooking behaviors. Of these participants, 57% responded that they will use food 

thermometers more regularly with meats, especially with poultry, and some respondents 

were committed to purchasing a thermometer: “Because like I said watching that video I 

was like, honestly, I was like, “damn. I need to get to Walmart and get a [laughter] meat 

thermometer.” That’s exactly what I thought to myself. I’ve been bad. All these years, 

never knew it [laughter].” 

About 33% of participants reported that watching the video will not influence their cooking 

behaviors in the future; however, 40% of the participants reported already using a 

thermometer when cooking meats. The most often cited reason (18% of participants) for 

not using a thermometer in the future is a reliance on other methods and general 

confidence in cooking experience and practices. Interestingly, one participant used a 

thermometer in the test kitchen but explained that she will not use it in the future—at least 

on thin cuts and burgers—because the thermometer reading in the kitchen supported her 

normal methods of doneness, “No, because I was right on target. I mean, it actually 

matched what I do. Now I am quite interested in using one for the turkey dinner. I would 

like to start using one for my pork roast because that’s something that, even after I cook it 

it’s still pink. And then I will fry it afterwards.” 

Approximately 83% of participants felt as if they related to either the people or situations in 

the video. The most common reasons included preparation of similar food items (34%), 

preparing home-cooked meals for dinners and leftovers (18%), and relating to the types of 

people/family structure in the video (16%). Approximately 17% of the participants felt that 

they did not easily relate to the people or situation in the video. About half of these 

participants reported that the family size in the video did not reflect their current situation 

because they only cook for themselves or one other person: 

▪ “I mean it’s not that they’re unrelatable, it’s just like, “Oh, we’re a happy little couple 

with our little kid and we cook at home every day,” and that’s not the way that I live 

I guess.” 

▪ “So, yeah, and the types of meals, too, because a lot of their meals were large scale 

for a family, and what I make is a little salad for one, one hamburger, one sandwich. 

So it’s different when you cook just for one person or you cook for four people.” 

▪ “I mean, I would like the nice food that they cooked, but I think they were a lot more 

competent in feeding a much bigger family than my family of me.” 

▪ “Not to me, because they’re young, a young family. I’m an older woman with a 

husband and a 42-year-old son that I cook for. So no, I really couldn’t relate to them 

because I’m totally different than they are. They seemed like a nice family, though.” 

One other reason cited for not relating to the people or situations included in the video was 

the use of a thermometer for all meals, specifically the casserole. Interestingly, one 

participant mentioned that she was surprised that the video failed to show what she 

3-25 
Meal Preparation Experiment Related to Thermometer Use 

considered standard chicken preparation practice: “I never saw her wash her meat. I didn’t 

see her wash that chicken, but I’m going to suppose that she did. I mean once you open the 

package then you wash everything, but I didn’t see none of that going on.” USDA does not 

recommend washing chicken before cooking because it can cause cross-contamination in 

the cooking environment. 

3.7 Additional Analysis 

We plan to conduct additional analyses of the post-observation interview data using NVivo 

to identify and code common themes in the information shared by participants. Additionally, 

we will associate common themes (nodes) with participant demographic data and conduct 

regression analyses to help identify whether there were trends among thermometer users 

compared with participants who did not use thermometers. Ultimately, we will determine 

the differentiators for whether a participant uses a thermometer or does not use one (e.g., 

whether the participant had prior experience with foodborne illness). We will provide the 

results of this analysis in a forthcoming manuscript. A separate forthcoming manuscript will 

provide information on the directional analysis of microbiological samples for each of the 

kitchen surfaces included in the microbiological analysis, similar to how the results are 

presented in Table 3-12. We plan to provide analyses on all paths related to how kitchen 

surfaces became contaminated. Although not a requirement of this contract, we envision 

our additional analysis to result in a total of five manuscripts to be co-authored with FSIS 

focusing on 1) handwashing, 2) evaluation of thermometer use and temperature behaviors 

and the intervention, 3) cross-contamination to RTE salad, 4) cross-contamination to food 

contact surfaces and the kitchen environment, and 5) results of the post-observation 

interviews and the predictive nature of self-reported antecedents on food safety behavior. 

3-26 
4. Discussion and Implications 

Section 4 concludes the report by discussing implications for message development that 

FSIS may want to consider as it refines 1) the messages and delivery mechanisms used to 

inform consumers on the importance of using a food thermometer and correct thermometer 

usage and 2) communications regarding other recommended food safety practices. These 

recommendations are based on the literature in combination with considering the results of 

this study. 

Consumers play a role in ensuring food safety 

CDC has identified contributing factors to foodborne illness including food from unsafe 

sources, improper holding/time and temperature, inadequate cooking, poor personal 

hygiene, and contaminated equipment/prevention of contamination; four of these factors 

are linked directly to food handler behaviors (Bean et al., 1996; CDC, n.d.). Five of the top 

10 food–pathogen combinations with the highest estimated annual disease burden are 

directly related to consumer handling (either controlled by cooking or reducing crosscontamination), and some of these combinations contain food groups that are regulated by 

USDA: poultry, pork, and beef (Batz, Hoffmann, & Morris, 2012). Pathogens such as 

Campylobacter and Salmonella can be fully controlled in consumer homes through cooking 

to safe internal temperatures and cross-contamination prevention. Risky preparation and 

handling of food have been linked to multiple outbreaks of foodborne illness and identified 

as a factor in public health burden (Nesbitt et al., 2009; Redmond & Griffith, 2003). 

More focus on proper thermometer usage 

It is encouraging that overall thermometer usage was high (54%) and participants were 

responsive to the video intervention (the control group used a thermometer 34% of the 

time, while participants who were exposed to the video used a thermometer to check 

doneness 75% of the time, significant at p < .001). Getting the message in front of 

consumers at decision-making time is important. 

Thirty-four percent of participants in the treatment group reported that the video did not 

influence their cooking behavior in the kitchen; however, 55% of these participants reported 

that they use a thermometer on a regular basis in their home kitchen, and the video simply 

reaffirmed this practice. There is likely some optimism bias here, because the most 

frequently cited reason (8%) for not using a thermometer in the test kitchen was the 

participants’ own experiences and confidence with other methods of determining doneness. 

Among total attempts to use a thermometer, 42% were correct (23% control, 52% 

treatment, significant at p < .001), which highlights the need for future materials to not just 

discuss thermometer use, but also demonstrate proper placement. The higher rate of proper 

4-1 
Meal Preparation Experiment Related to Thermometer Use 

placement by the treatment group compared with the control group suggests that the 

information in the video on proper placement was useful to some participants. 

More emphasis on not using subjective indicators to determine doneness 

Previous studies looking at popular cooking shows have similarly found that subjective 

indicators (e.g., color, touch) are more commonly used to determine doneness than 

thermometers (Borda et al., 2014; Maughan, Chambers, & Goodwin, 2016; Mathiasen, 

Chapman, Lacroix, & Powell, 2004; Woods & Bruhn, 2016). A study of egg-based recipes 

also showed that recipes used a variety of indicators not related to temperature, but most 

frequently time (Godwin, Maughan, & Chambers, 2016). Relying on subjective indicators is 

a riskier way to determine doneness because some indicators, like the color of meat and 

poultry and their juices, do not correlate with safe internal cooking temperatures (Hague et 

al., 1994; Røssvoll et al., 2014). Some sources of cooking information match gradations 

(e.g., rare, medium rare, medium, medium well, well done) to internal cooking 

temperatures as well as visual descriptions, but no peer-reviewed scientific evidence 

supports these temperature gradations. Educational materials on thermometer use should 

continue to emphasize that subjective indicators of doneness are not reliable, and using a 

food thermometer is the only way to ensure foods are cooked to a safe internal 

temperature. 

Further need to improve clean, separate, and chill behaviors 

In addition to the message cook, the study collected information on the other key food 

safety messages of clean, separate, and chill to provide FSIS with information for yearover-year comparisons during later phases of the study. The study results described in this 

report suggest that improvements are warranted in these behaviors based on observed 

behavior and the results of microbiological sampling (for the clean and separate messages) 

and self-reported usual behavior (for chill messages). 

Clean. We observed 2,249 cases in which a handwashing event was required to control 

pathogens; of these, handwashing was attempted 31% of the time. Among handwashing 

events attempted, only 4% of attempts contained all steps of a correct handwashing event. 

A study using survey data and propensity score matching methodology found that washing 

hands with soap before food preparation leads to a reduction in the probability of reported 

foodborne illness (Ali, Verrill, & Zhang, 2014). 

Separate. The spice containers were the most frequently contaminated sample of those 

analyzed to date: approximately 50% of participants contaminated these surfaces 

(independent of control/treatment). While coding for behaviors leading up to their 

contamination is yet to occur, it is likely that participants handled raw turkey patties 

immediately before they picked up the spice containers to season the patties. The faucet 

handle was contaminated approximately 12% of the time (independent of 

4-2 
Section 4 — Discussion and Implications 

control/treatment). A total of 78 participants used their mobile devices at some point after 

handling turkey packaging, and six devices were contaminated. It is not known how long 

pathogens can remain viable on mobile devices, and future studies could explore how long 

pathogens stay viable on different materials, including phones/phone covers, to determine 

the significance of this to public health. 

The relatively low rate of contamination of salad lettuce (6%) indicates that crosscontamination was not necessarily frequent but did occur with some regularity. Preliminary, 

although as yet incomplete, coding of the observations suggests that a missed or failed 

handwashing attempt was part of the sequence that led to cross-contamination of the salad 

lettuce. Direct contamination of the salad lettuce by the turkey patties seems much less 

likely to be the contaminant source, in contrast to contamination of the spice containers, 

which was likely direct. 

Chill. Many participants self-reported following USDA-recommended practices for thawing 

meat or poultry (79% for treatment group and 81% for control group), and most reported 

they would cook or discard the product if it was not cooked within 2 days, as recommended. 

About half of participants self-reported storing leftovers in multiple small containers, as 

recommended (55% for treatment group and 46% for control group), and few refrigerate 

the leftovers immediately (8 to 12%) and instead let the leftovers cool before placing them 

in the refrigerator. 

More knowledge is not the key, it is actionable skills and compelling reasons 

Verbeke, Frewer, Scholderer, and De Brabander (2007) reported that experts in food risk 

management tend to view the general public as deficient in understanding food hazards and 

associated risks; the general public displays behavioral patterns and makes choices that 

seem irrational or illogical or at least inconsistent with expert opinions and scientific 

knowledge. As noted by Bob Lalasz, the director of science communication for the Nature 

Conservancy regarding the public’s response to scientific innovations and influences on 

behavior, there is the assumption by experts that “the public isn’t getting the gravity of the 

problem—because if they did, how could they fail to act?” (Contractor & DeChurch, 2014). 

In other words, to connect directly to food safety risks, if people had more knowledge of or 

a different attitude about foodborne illness risks, their food safety practices would improve. 

However, this deficit-of-knowledge premise has been criticized for its lack of appreciation of 

the social, cultural, and practical complexities in which consumers’ everyday practices are 

embedded (Halkier & Jensen, 2011) and is not supported by evidence. Generally, people do 

not respond to information in the straightforward way that communicators hope; 

communicators need to examine how people will think about and use the information they 

provide and relate that information to peoples’ everyday lives (Eden, Bear, & Walker, 2008). 

People often respond differently to messages about risk than communicators expect; hence, 

to effectively communicate about risk, communicators must consider how people will think 

4-3 
Meal Preparation Experiment Related to Thermometer Use 

about and use the information provided (Eden et al., 2008). Bruhn (2005) argued that risk 

communicators should first identify the full range of audiences, describe how risk is 

determined and monitored, and show how risk can be controlled or reduced. To be effective, 

messages must be tailored to an audience’s needs, concerns, and interests (Lundgren, 

1994). 

Communications efforts will be wasted if people already know the information or consider it 

irrelevant (Fischhoff & Downs, 1997). Providing generalized risk messages will be 

ineffective, unless the risk affects everyone equally (Cope et al., 2010). Messages about 

risks should be clear and specific and tailored for the audience’s estimated level of 

comprehension (Lundgren, 1994; Covello, 2003). Galarace and Viswanath (2012) 

recommended that communication planners be mindful of factors related to the 

communication process, such as culture, gender, age, language, race/ethnicity, and income 

and education levels of the target audience, as well as factors that might influence 

implementation of desired behaviors, including financial resources, location, transportation, 

and health care access. Combining written, verbal, and visual formats can also improve 

effectiveness (Durant, 2002). Important points should be highlighted throughout the 

material and information presented should be concise and written in plain language. 

Research suggests that many people misunderstand quantitative information, leading to a 

misinterpretation of risk (Cunningham & Boom, 2013). Providing too much information is a 

common problem (Foster & Käferstein, 1985) and should be avoided; messages that are 

difficult to decipher or burdensome to receive are easily ignored (Verbeke, 2005). Research 

indicates that people can have difficulty remembering more than three messages, and recall 

of technical messages may also be poor (Sugerman et al., 2012). 

Although information is a prerequisite to action, knowledge does not always translate into 

action (Rudd, Comings, & Hyde, 2003). Consumer motivation to take action is increased by 

the perception of a personal ability to control risk (Redmond & Griffith, 2003; Mullan & 

Wong, 2009). Messages that provide direction and to which audiences can personally relate 

are particularly persuasive (Frewer, Howard, Hedderley, & Shepherd, 1997; Eden et al., 

2008). Perceptions about food-related risks are influenced by cultural and social factors 

(Knox, 2000). Risk communicators who do not consider factors that affect the way the 

general public perceives risks are unlikely to foster the appropriate level of risk perception 

(Verbeke et al., 2007). People tend to categorize risks as tolerable or intolerable according 

to subjective attributes, including familiarity and perceived catastrophic potential (Rodricks, 

2002; Lofstedt, 2006). This suggests that people’s familiarity with food and cooking in the 

home could influence their perceived risk of foodborne illness. 

Even with careful attention to message framing and language, consumers may find it 

difficult to apply risk control measures in their daily practices. Wills, Meah, Dickinson, and 

Short (2015) studied domestic kitchen practices to gain insight on how food stored, 

prepared, and eaten in the home may contribute to foodborne disease. They observed that 

4-4 
Section 4 — Discussion and Implications 

kitchen practices were entangled in people’s habits and cultural practices and were 

embedded within sequences comprising many small events that also included non-foodrelated activities. Their study found that food preparation, laundry, childcare, pet care, 

social life, school and office work, arts and crafts activities, music practice, reading, 

gardening, and bicycle repairs also took place in people’s kitchen spaces. Cleaning was one 

action carried out within these sequences of events, but its purpose was to make the area 

tidy and nice, or cleaning was part of a habitual routine rather than to prevent foodborne 

illness. The youngest children, oldest adults, and family pets were all engaged in the 

kitchen, which has implications for preventing foodborne diseases as well. 

Meah (2014) also collected qualitative and ethnographic data to examine how concerns 

about food safety were negotiated into everyday domestic kitchen practices in the United 

Kingdom and found that common sense logic was used to balance food safety against 

experiential knowledge and sustainability concerns (e.g., reducing food waste). These 

findings conflict with the widely held assumption that consumers’ failures to follow safe food 

handling instructions are often due simply to a lack of knowledge (Verbeke et al., 2007). 

Meah (2014) proposed that authorities’ advice would have more impact if it took more 

account of consumers’ practical knowledge and routine practices and incorporated current 

levels of public understanding and knowledge base rather than assuming a deficit of 

knowledge. 

Using narratives to convey food risk information and provide context within peoples’ lives 

can help individuals better understand their role in controlling risk (Jacob et al., 2010). 

Storytelling is a basic form of human interaction, and one of the oldest techniques for 

transmitting knowledge (Hinyard & Kreuter, 2007). It plays an important role in making 

sense of experiences and interpreting the world (Matthews & Stephens, 2010). Compared 

with scientific information, stories relate life lessons and values and are effective because 

they are relatable and easily remembered (Cunningham & Boom, 2013). The use of 

narratives in foodservice settings has been shown to influence food safety behaviors of food 

handlers, increasing handwashing frequency and reducing cross-contamination events 

(Chapman et al., 2010). Elements of surprise, such as humorous graphics or sobering data, 

can help make the narrative memorable (Chapman et al., 2010). Emphasizing the human 

rather than statistical aspects can increase the interest and relevance of the information to 

an audience (Food and Agriculture Organization, 1999), and identifying individual victims 

enhances the perception of personal risk (Covello, Peters, Wojtecki, & Hyde, 2001). 

Recapping a persuasive narrative with a nonnarrative summary may help reinforce the takeaway messages (Slater & Rouner, 2002). 

General information about risk is not enough; consumers will practice safe food behavior 

only when they perceive a direct risk to themselves. Consumer knowledge and awareness of 

foodborne illness and pathogens do not always result in a positive change in food handling 

behavior. It is thus important to learn more about consumer attitudes and behaviors to 

4-5 
Meal Preparation Experiment Related to Thermometer Use 

create awareness of safe food handling practices, to promote public trust and credible 

information sources, to encourage food safety education, to create familiarity, and to 

incorporate everyday context into food safety communications. Foodborne illness prevention 

messages should stimulate perceptions of risk and bolster self-efficacy to increase the 

adoption of safe food handling behaviors. Food safety messages for consumers should 

address the behaviors that lead to the highest incidence of foodborne illness causing the 

most serious consequences. Risk messages directed to specific concerns are more relevant 

to the public than general messages. Consumers may be more receptive to risk 

communication and education messages at “teachable moments,” for example, following 

publicized outbreaks of foodborne illness. 

4-6 
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Appendix A: 

Screening Questionnaire 

Hello. My name is _______________. Thank you for your interest in our research study, 

which is funded by the U.S. Department of Agriculture and conducted by researchers from 

North Carolina State University and RTI International. 

If you are eligible for the study, you will be asked to prepare two recipes while being 

videotaped and participate in an interview at a day and time convenient for you. The study 

will last no more than 2 hours, and you will receive $75 and a small gift for taking part in 

the study. 

To determine whether you are eligible, I need to ask you a few questions. These questions 

will take less than 10 minutes to complete. Your participation in this study is completely 

voluntary. All of your answers and your contact information will be kept private. 

May I please ask you a few questions to determine whether you are eligible to participate in 

our study? 

☐ Yes 

☐ No → Refusal. Terminate. 

1. Great! Let’s get started then. When it comes to grocery shopping in your household, 

would you say...? (Read list. Select one.) 

☐ You do all of it. 

☐ You do most of it. 

☐ You do about half of it. →Ineligible. Terminate. 

☐ Someone else does most of it; you do some of it. →Ineligible. Terminate. 

☐ Someone else does all of it. →Ineligible. Terminate. 

2. Have you ever received any type of food safety training, such as ServSafe? (Select 

one.) 

☐ Yes → Ineligible. Terminate. 

☐ No 

3. Have you ever cooked or worked professionally in a food preparation setting? (Select 

one.) 

☐ Yes →Ineligible. Terminate. 

☐ No 

4. Are you a vegetarian or vegan? (Select one.) 

☐ Yes → Ineligible. Terminate. 

☐ No 

5. How many times per week do you prepare a meal at home? (Read list. Select one.) 

☐ Never →Ineligible. Terminate. 

☐ 1 to 3 times per week → Ineligible. Terminate. 

☐ 4 or more times per week 

6. In the past three months, have you, yourself, prepared and cooked a meal using any of 

the following foods? (Read list. Select all that apply.) 

☐ Raw turkey or chicken 

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Meal Preparation Experiment Related to Thermometer Use 

☐ Raw beef 

☐ Raw pork 

☐ None of the above (DO NOT READ) → Ineligible. Terminate. 

7. When following a recipe for the first time, do you...? (Read list. Select one.) 

☐ Read the whole recipe before you start cooking 

☐ Read the recipe while you are cooking 

8. Which of the following items do you have in your kitchen? (Read list. Select all that 

apply.) 

☐ Chef’s knife 

☐ Garlic press 

☐ Citrus zester 

☐ Food thermometer to check the doneness of meat/poultry 

☐ Manual can opener 

☐ Can puncher 

☐ Cheese grater 

☐ Wine opener 

☐ Corkscrew 

☐ None of the above (DO NOT READ) 

9. Imagine you are cooking hamburgers at home for dinner. How do you determine 

whether the burgers are done and ready to eat? Do you...? (Read list. Select all that 

apply.) 

☐ Rely on cooking time 

☐ Insert a knife, toothpick, or other utensil into one of the burgers, and check to see 

that it comes out clean 

☐ Use a food thermometer 

☐ Cut one of the burgers and check that it is no longer pink or red in the middle 

☐ Check that the outside of the burger is the right brownness 

☐ Touch one of the burgers with your finger to see if it is firm 

☐ Taste one of the burgers 

10. Which of the following categories best describes your age? (Read list. Select one.) 

☐ Under 18 →Ineligible. Terminate. 

☐ 18 to 34 [RECRUIT 28%] 

☐ 35 to 54 [RECRUIT 36%] 

☐ 55 or older [RECRUIT 36%] 

11.Are you Hispanic or Latino? (Select one.) 

☐ Yes [RECRUIT 17%] 

☐ No [RECRUIT 83%] 

A-2 
 

 

Appendix A: Screening Questionnaire 

12. What is your race? (Read list. Select all that apply.) 

☐ American Indian or Alaska Native 

☐ Asian 

☐ Black or African American 

☐ Native Hawaiian or Other Pacific Islander 

☐ White [RECRUIT ≤74%]

13. What is the highest level of education that you have completed? (Read list. Select 

one.)8 

☐ Less than high school or high school graduate or GED [RECRUIT 42%] 

☐ Some college or 2-year degree [RECRUIT 29%] 

☐ College degree [RECRUIT 18%] 

☐ Post-graduate degree [RECRUIT 11%] 

14. Do you have any children living in your household who are less than 18 years of age? 

(Select one.) 

☐ Yes [RECRUIT 66%] 

☐ No [RECRUIT 34%] 

15.Are you or any members of your household ...? (Read list. Select all that apply.) 

☐ 60 years of age or older 

☐ 5 years of age or younger 

☐ Pregnant 

☐ Breastfeeding 

☐ Diagnosed with an allergy to any food or food ingredient 

☐ Diagnosed with diabetes or kidney disease 

☐ Diagnosed with a condition that weakens the immune system, such as cancer, HIV, 

or AIDS; a recipient of a transplant; or receiving treatments, such as 

chemotherapy, radiation, or special drugs or medications to treat these conditions 

☐ None of the above (DO NOT READ) 

16. Where did you hear about this study? (DO NOT READ. Select all that apply.) 

☐ Post on social media 

Specify: __________________________ 

☐ Email from the Expanded Food and Nutrition Education Program 

☐ Sign in grocery store 

☐ Don’t know 

17. Great! You qualify for the study. Would you like to participate in the study? 

☐ Yes 

☐ No → Terminate. 

Great! We are conducting the interviews the week of [DATE]. The interviews will be held 

each day between [TIME] and [TIME]. The study will last no more than 2 hours, and you will 

receive $75 and a small gift for taking part in the study. What day and time is convenient 

for you to participate? 

8 Toward the end of data collection, we revised the screening criteria to include people with a technical 

or vocational training in the “Less than high school or high school graduate or GED” category. 

A-3 
Meal Preparation Experiment Related to Thermometer Use 

[SCHEDULE DAY AND TIME] 

I have you scheduled for [DATE] at [TIME]. Your interview will last 2 hours and will be 

held on NC State’s campus. May I please have your name, telephone number, and 

email address so we can send you a confirmation email with directions? 

[ENTER NAME] 

[ENTER TELEPHONE NUMBER] 

[ENTER EMAIL ADDRESS]. 

☐ No Email 

[If no email] May I please have your mailing address? [ENTER STREET ADDRESS, CITY, NC, 

ZIP] 

Thank you for your time. 

If you have any questions about the study or need to reschedule or cancel, you may contact 

[NAME] at [PHONE NUMBER]. If you have concerns about how participants are being treated 

in the study, you may contact North Carolina State University’s Office of Research Protection 

at 919-515-4514. 

Ineligible/Terminate Screen 

Thank you for your time. Unfortunately you are not eligible to take part in our study. Have a 

great day. 

According to the Paperwork Reduction Act of 1995, an agency may not conduct or sponsor, 

and a person is not required to respond to, a collection of information unless it displays a 

valid OMB control number. The valid OMB control number for this information collection is 

0583-0169 and the expiration date is 06/30/2018. The time required to complete this 

information collection is estimated to average 8 minutes per response, including the time for 

reviewing instructions, searching existing data sources, gathering and maintaining the data 

needed, and completing and reviewing the collection of information. 

A-4 
Appendix B: 

Observation Script and Recipes 

Check-in Script 

Welcome! My name is , and I’ll be walking you through what you’ll be doing as part of our 

study today. 

Today you will be preparing two recipes: a salad and turkey burgers, and we will interview 

you after you finish cooking. The cooking and interview will last no more than 2 hours total. 

Before we start, I need you to read and sign the consent form. Please let me know if you 

have any questions or concerns. You will receive a copy of the form to take home. 

We have a few more items to prepare before you begin. While you wait, please watch this 

video (provide iPad, video depends on random number assignment for participant). 

Observation Script 

Hello, my name is _______, and I’ll be walking you through what you’ll be doing as part of 

our study today. 

Today you will be preparing two recipes to test a new product formulation: a salad and 

turkey burgers. The recipes are provided on this card, one recipe is on the front and one is 

on the back. Prepare the foods in the order that you would usually do so at home. 

After preparing the recipes, please clean up the kitchen as you normally would at home. 

We will interview you after you are finished cooking. The cooking and interview will last no 

more than 2 hours total. 

This is the area where you will be cooking. All the available utensils and dishes are in these 

drawers/cabinets (indicate). Feel free to use whatever you need. Please make yourself at 

home, you are welcome to use your phone to listen to music, or whatever you usually do 

when cooking at home. 

Restrooms are located ______, and in case of an emergency, the exits are ______. The fire 

extinguisher is located ________ , and the first aid kit is located _________________. 

Before you begin, do you have any questions? 

If you have any questions or concerns while you’re cooking, I will be in the office next door. 

Before you eat anything, please let us know when you are finished cooking by pushing this 

button. 

[after cooking] 

Now that you have finished the cooking portion of the study, we are ready to begin the 

interview. It should take no more than 20 minutes to complete. Do you need a break before 

we begin that portion? 

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Meal Preparation Experiment Related to Thermometer Use 

[Note: The two recipes were printed front-and-back on a laminated card.] 

Turkey Burger Recipe 

Ingredients 

For the patties: 

● 2 turkey burger patties 

● Salt 

● Pepper 

● Garlic powder 

● Onion powder 

For serving: 

● Hamburger buns 

● Sliced tomato 

● Sliced onion 

Directions 

1. Season the burger patties with salt, pepper, garlic powder and onion powder on both 

sides. 

2. Cook the burgers at medium-high heat to your desired level of doneness. 

3. Assemble cooked burgers with sliced tomato and sliced onion 

Chef’s Salad 

Salad Ingredients 

● 2 stalks romaine lettuce 

● Salt and pepper 

● 1 cup dressing (recipe below) 

● 3/4 cup shredded Swiss cheese 

● 3/4 cup ham 

● 1 hot house tomato 

Dressing Ingredients 

● 1/2 cup olive oil 

● 1/4 cup balsamic vinegar 

● 1 teaspoon honey 

● 1 teaspoon Dijon mustard 

● 1 shallot, minced 

● 1 clove garlic, minced 

● Salt and ground pepper to taste 

Directions 

1. Cut lettuce into bite-size pieces 

2. Cut ham into matchstick-sized pieces 

3. Dice tomato 

4. Mix all ingredients together 

5. Serve with dressing on the side 

B-2 
Appendix C: 

Post-observation Interview Guide 

Post-observation interview guide 

ID No: Date: 

Treatment group Y/N 

Introduction script: 

Thank you so much for your time today and allowing us to record your actions while you 

prepared a meal just like you would in your home. If it is okay with you, I’m going to ask 

you a few follow-up questions that will focus on some of the activities you participated in 

while in the model kitchen. 

Is it okay with you if I record your answers? The recording is confidential and will only be 

used to accurately capture our conversation (allowed recording y/n). 

We mentioned in our recruiting materials that we were interested in cooking practices and 

how you evaluate recipes. However, the specific focus of our study is on food safety and 

how to prevent food poisoning. The aim of this study is to measure handling and 

preparation practices and investigate the movement of bacteria from raw foods, so we 

can better understand exactly how contamination can spread. In addition, a biological 

tracking agent was in the food to help us track where contamination might occur. This 

biological tracking agent is a bacteriophage called MS2, and it does not pose any health 

hazard to you. We purposely did not tell you exactly what our specific research objectives 

were in advance to capture your behaviors in a natural way. You can request to be 

removed from the study at any time, and if you decide to exit the study at this point, we 

will destroy the recordings of your actions, and you will not be included in the data set. 

We want to confirm with you now that you understand the focus of our study and that 

you wish to remain as a participant. 

If no: Thank you so much for your time, your participation in our study is now complete, 

and we will remove your data from our dataset and destroy any records. 

If yes: Thank you for your consent. 

If it is okay with you, I’d like to begin this interview, which will take about 20 minutes. 

A study team member is collecting micro samples from the kitchen surfaces and 

equipment. We noticed you touched your [device] while cooking, would you mind if we 

took a swab of your phone? 

If no: no problem. 

If yes: thank you. 

Observation follow up (semi-structured, to be filled in by observer during the meal 

preparation to allow for in-depth information specific actions and values). 

[Provide context] I saw that you washed your hands before you started cooking today, 

can you tell me why you did that? Is that something you typically do when cooking at 

home? Why? 

Or 

[Provide context] I saw that you did not wash your hands for a full 20 seconds before 

cooking today, can you tell me why not? When you cook at home, do you usually not 

wash your hands before cooking? Why not? 

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Meal Preparation Experiment Related to Thermometer Use 

[Provide context] I saw that you used a food thermometer today, can you tell me why 

you used it? What information were you looking for? Is that something you typically do 

when cooking at home? Why? 

[If participant mentions referring to label/cooking directions] Do you recall what you 

read? [Probe to see if referring to Safe Handling Instructions vs. cooking directions 

provided by manufacturer] 

[If participant does not mention referring to label/cooking directions] Did you notice any 

cooking instructions on the label. If yes, do you recall what it said? [Probe to see if 

referring to Safe Handling Instructions vs. cooking directions provided by manufacturer] 

How important do you think it is to use a food thermometer when cooking? Would you 

say ... 

Very important 

Somewhat important 

Not important at all 

[Don’t know] 

Or 

[Provide context] I saw that you did not use a food thermometer today, can you tell me 

why not? Do you usually not use a thermometer when cooking at home? Why not? 

How do you usually determine doneness? 

[If participant mentions referring to label/cooking directions] Do you recall what you 

read? [Probe to see if referring to Safe Handling Instructions vs. cooking directions 

provided by manufacturer] 

[If participant does not mention referring to label/cooking directions] Did you notice any 

cooking instructions on the label. If yes, do you recall what it said? [Probe to see if 

referring to Safe Handling Instructions vs. cooking directions provided by manufacturer] 

How important do you think it is to use a food thermometer when cooking? Would you 

say ... 

Very important 

Somewhat important 

Not important at all 

[Don’t know] 

[Provide context] I saw that you washed your hands after handling raw meat/poultry 

today, can you tell me why you did that? Is that something you typically do when cooking 

at home? Why? 

Or 

[Provide context] I saw that you did not wash your hands after handling raw meat/poultry 

today, can you tell me why not? When you cook at home, do you usually not wash your 

hands after handling raw/meat poultry? Why not? 

C-2 
Appendix C: Post-observation Interview Guide 

[Provide context] I saw that you washed the cutting board and utensils today with soap 

and water, can you tell me why you did that? Is that something you typically do when 

cooking at home? Why? 

Or 

[Provide context] I saw that you did not wash the cutting board and utensils today with 

soap and water, can you tell me why not? When you cook at home, do you usually not 

wash the cutting board with soap and water? Why not? 

[Provide context] I saw that you touched your [device] while cooking. Is that something 

you typically do when cooking at home? Why? 

Or 

[Ask if device was accessible, but not used] I saw that you didn’t touch your [device] 

while cooking. When you cook at home, do you usually avoid touching your [device]? 

Why? 

Imagine you just cooked a large pot of soup or chili so that you would have enough to eat 

the next day. What do you do with the leftovers? 

Probe: Do you place the leftovers in one container or multiple containers? How big are the 

containers? 

Probe: Do you refrigerate the leftovers immediately or wait awhile to put them in the 

refrigerator? How long do you wait? 

How long do you store the leftovers in the refrigerator before someone eats them or you 

throw them away? 

Imagine you have meat or chicken in the freezer, and you plan to cook it for dinner later 

in the week. How would you thaw it? 

Probe: Do you thaw it the day you’re cooking it or a couple days before? 

Probe: What method of thawing do you use: in the microwave, in the refrigerator, in 

water in the sink, or on the countertop? 

If water in sink, do you use hot or cold water? Running or standing water? Do you change 

the water at some point? When do you cook it? 

If in refrigerator, where do you place the frozen meat? On the top, bottom, or middle 

shelf? What, if anything, do you place it on? When do you cook it? 

If in the microwave, do you cook it immediately or wait awhile before cooking it? How 

long do you wait? 

Let’s say you thawed the meat or poultry for dinner tonight, but something came up and 

you were not able to cook it. How many days would you leave it in the refrigerator before 

cooking it or throwing it away? 

C-3 
Meal Preparation Experiment Related to Thermometer Use 

Antecedents 

How concerned are you about bacteria or viruses on or inside the food you cook? On a 

scale of 1-7, with 1 being not at all concerned, 4 being neutral, and 7 being extremely 

concerned, how concerned are you? 

Do you feel like you have control in your home about the safety of the food you cook? 

Why or why not? 

Have you ever had food poisoning? Y/N 

Follow-up: Can you tell me about your experience? What were the symptoms, what food 

do you think made you sick? Do you believe your illness was contracted from cooking at 

home, or eating prepared food away from home? 

Of the following three statements, which one is closer to your view...? 

▪ Certain types of people have a higher risk of getting food poisoning 

▪ It depends, certain types of people are at higher risk for some types of food 

poisoning [Probe: what types of people are more likely to get sick?] 

▪ All types of people have about the same risk of getting food poisoning 

▪ Don’t know 

How common do you think it is for people in the United States to get food poisoning 

because of the way food is prepared in their home? Would you say that it is... 

▪ Very common 

▪ Somewhat common 

▪ Not very common 

Has a family member ever had food poisoning? Y/N 

Follow-up: Can you tell me about his/her experience? What were his/her symptoms, what 

food do you think made him/her sick? Do you believe their illness was contracted from 

eating at home, or eating prepared food away from home? 

Intervention specific follow-up (treatment group) 

Think back to the second video we showed you today, what were the key takeaway 

points? (may need to show the start of the video again as a reminder, not the full video) 

Did watching the video influence your actions in the kitchen today or not? If yes, in what 

way? 

Do you think the video will influence how you cook at home in the future, or not? Why? 

Do you relate to the situations and the people shown in that video or not? Explain. 

C-4 
Appendix C: Post-observation Interview Guide 

Intervention specific follow-up (control) 

We are planning on creating educational material about safe food handling. What 

messages would you want to see in these materials? 

What situations and topics would you want to see in this material to make it relevant to 

you? 

How do you usually get information on how to safely prepare food when cooking at home? 

How would you like to get information on how to safely prepare food when cooking at 

home? 

Conclusion 

Thank you again for your time and for your participation in our study today. Are there any 

questions that you have for me? 

Please see the greeter on your way out to receive the $75 and gift. 

C-5 

Appendix D: 

List of Equipment Provided in Each Test Kitchen 

The picture below shows one of the test kitchens used for the meal preparation experiment. 

The equipment provided in each test kitchen is listed below. 

Kitchenware 

Grill 

❏ George Foreman grill 

Skillet 

❏ Medium sized skillet (9-12 inch) 

Frying pans (store frying pans in the cabinets) 

❏ Small (8 inch) non-stick 

❏ Medium or large (10-12 inch) 

Sauce pans 

❏ Small (2-3 quarts) 

❏ Medium or large (4-5 quarts) 

D-1 
Meal Preparation Experiment Related to Thermometer Use 

Knives 

❏ Chef’s knife 

❏ Paring knife/fruit knife 

Baking dishes 

❏ 9x13 baking dish (rectangular) 

❏ Smaller square, rectangular, or oval baking dish 

Utensils 

❏ Wooden or plastic stirring spoons (1-2) 

❏ Heat-resistant plastic or silicone spatula 

❏ Slotted spoon 

❏ Ladle 

❏ Flat spatula (for flipping burgers) 

❏ Cooking tongs 

❏ Digital tip-sensitive instant read thermometer 

❏ Dry measuring cups 

❏ Liquid measuring cup (1 cup) 

❏ Measuring spoons 

❏ Can opener 

❏ Liquid measuring cup (2 cup) 

❏ Whisk 

❏ Rolling pin 

❏ Peeler 

❏ Zester/grater 

❏ Large cutting boards 

❏ Splatter guard 

❏ Serving bowl 

❏ Serving utensils (serving fork, spoon, and tongs) 

❏ Salt and pepper shaker (must be glass) 

❏ Garlic and onion powder 

❏ Utensil holder 

Other essential tools 

❏ Small, medium, and large mixing bowls 

❏ Colander 

❏ Salad spinner 

Silverware/Dinnerware 

❏ Set of spoons, knives and forks 

❏ Dinner plates 

❏ Salad plates 

❏ Bowls 

Cleaning/dishwashing supplies 

❏ Kitchen towels 

❏ Dish cloths 

D-2 
Appendix D: List of Equipment Provided in Each Test Kitchen 

❏ Hand soap 

❏ Dish drain board/dish rack 

❏ Paper towels 

❏ Sponge 

❏ Sponge caddy 

❏ Paper towel holder 

❏ Apron 

❏ Oven mitts 

❏ Pot holders 

❏ Dishwashing detergent 

Cleaning stuff for under sink 

❏ Bucket 

❏ Windex 

❏ Simple green cleaner 

❏ Clorox bleach 

❏ 409 cleaner 

❏ Lysol spray 

Leftover kit supplies 

❏ Ziploc bags (gallon and quart sizes) 

❏ Plastic wrap 

❏ Plastic containers with lids 

Note: Containers must be sanitized between observation events. Ziploc bags and plastic 

wrap must be taken out of retail packaging and placed in kitchen drawers. 

Housekeeping items 

❏ Trash can for kitchen (13 gallon, with a cover but no step to open feature). Note: 

position the trash can near the cooking area. 

❏ Trash bags (13 gallon) 

❏ First-Aid Kit 

❏ Label maker 

❏ Toolbox 

Electronics 

❏ Tool boxes 

❏ Gaffer tape 

❏ Blue painter’s tape 

❏ Super glue 

❏ Scissors 

❏ HDMI cable (25 feet, 2x) 

❏ HDMI female-to-female adapter 

❏ Zip ties (11 inch) 

❏ Surge protector (2x) 

❏ Gallon Ziplocs 

❏ AAA batteries (batteries for label maker) 

❏ AA batteries (batteries for mouse) 

D-3 
Meal Preparation Experiment Related to Thermometer Use 

Paperwork 

❏ Gift cards 

❏ Thermometers 

Cameras 

❏ Tripods 

D-4 
Appendix E: 

Power Analysis 

The purpose of the meal preparation study was to evaluate the impact of FSIS educational 

materials on consumers’ demonstrated use of recommended safe food handling practices 

(clean, separate, cook, and chill). For the initial iteration of the study, the primary outcome 

of interest is use of a food thermometer to check the doneness of meat and poultry. Using a 

food thermometer is an important but not commonly practiced behavior in American 

kitchens. Based on recent estimates, we anticipated observing food thermometer use 5% of 

the time among the control group participants (Anderson et al., 2004; Phang & Bruhn, 

2011; Bruhn, 2014; Mazengia, Fisk, Liao, Huang, & Meschke, 2015; Scott & Herbold, 2010). 

Additionally, we anticipated that the food safety messaging materials will provide medium 

effects among the treatment group participants. Table E-1 provides potential observed 

differences between the control and treatment groups ranging from 4 to 12 percentage 

points. We anticipated that the food safety messaging materials will be sufficient to 

generate differences in the middle of this range (i.e., the observed difference between the 

control and treatment groups is 8 percentage points); thus, the study design used a sample 

size of 400 (200 in each group). 

Table E-1. Sample Size Requirements for Different Observed Differences 

between the Control and Treatment Groups 

Observed 

Difference 

Proper Proper Between Control 

Thermometer Use: Thermometer Use: and Treatment Total Sample Size 

Control Group Treatment Group Groups (N) 

5% 9.0% 4% 1,270 

5% 11.0% 6% 636 

5% 13.0% 8% 394 

5% 15.0% 10% 276 

5% 17.0% 12% 206 

E-1 

 

 

Appendix F: 

Microbiological Methods 

F.1 Preparation of Bacteriophage MS2 Stocks 

We prepared bacteriophage MS2 (ATCC 15597-B1) stock solutions using the double agar 

method as described in National Science Foundation standard 55 (Badman, 2001) and 

Tung-Thompson, Libera, Koch, de los Reyes, & Jaykus (2015). We plated ten-fold serial 

dilutions of MS2 on tryptic soy agar (TSA) supplemented with 0.1% glucose, 2 mM CaCl2, 

and 10 μg/ml thiamine and incubated it overnight at 37°C. We flooded plates showing 

complete lysis with 3 ml of tryptic soy broth (TSB) and scraped off the soft agar layer into a 

sterile 50 ml tube. We increased the volume to 40 ml with TSB and added 0.2 g EDTA and 

0.026 g lysozyme to each tube. We incubated the tubes for 2 hours at 37°C with shaking. 

We recovered the supernatant by centrifugation at 9,300 x g for 10 min followed by filter 

sterilization using a 0.22 μm filter. We enumerated the stocks as described below. We

considered aliquots of this supernatant as high titer MS2 stock (approximately 1010 plaqueforming units per milliliter [PFU/ml]). We aliquoted the stocks and stored them at −80°C

until use. 

F.2 Enumeration of Bacteriophage MS2 Stocks 

We enumerated the MS2 stocks using the double agar layer method in accordance with the 

method of Su and D’Souza (2011) with minor modifications. Briefly, we incubated the E. coli 

C3000 host for 4 to 6 hours with gentle shaking (100 RPM, 37°C). Simultaneously, we 

melted 8 mL tubes of 0.6% TSA and tempered them in a 42°C water bath. We allowed 

previously prepared petri dishes containing 1.2% TSA to warm to room temperature. Then, 

we prepared 10-fold serial dilutions of MS2 stock. We added a volume of 0.7 mL of each 

dilution to the tempered 8 ml TSA tube after which we added 0.3 ml of E. coli solution, and 

we quickly vortexed the suspension and poured it on top of the 1.2% TSA plates. Upon 

solidification, we inverted the plates and incubated them overnight at 37°C and then 

counted plaques. Counts are expressed as plaque-forming units per milliliter. We also 

processed serially diluted MS2 stocks for nucleic acid extraction and RT-qPCR quantification 

as described in Section F.6 to produce a standard curve. Plaque-forming units were plotted 

against corresponding cycle threshold (CT) values and analyzed by linear regression to 

produce the standard curve. We produced the standard curve by three independent RTqPCR assays. 

F.3 Spiking Meat Products with Bacteriophage MS2 

We used MS2 stocks prepared according to the steps described in Section F.1. The raw 

meat/poultry food products were spiked with MS2 at a concentration of 108 plaque-forming 

units/gram of meat (PFU/g) during the grinding process, performed at NCSU as described 

F-1 
Meal Preparation Experiment Related to Thermometer Use 

by Porto-Fett et al. (2016). We prepared meat products and acquired them on a weekly 

basis during the study. We sanitized the meat laboratory after production using the methods 

outlined in Section F.7. 

F.4 Environmental Swabbing and Lettuce Sample Collection 

During each observation, we collected a minimum of 10 environmental samples, one food 

sample (either lettuce in the RTE salad if it was prepared after the burger or lettuce from 

the burger if the RTE salad was prepared before the burger),9 and one sample preobservation to validate cleaning. We collected up to two additional environmental samples 

based on the behaviors of the person being observed; the observing coder determined the 

additional site(s) for sampling, if required, and based this determination on the behavior 

observed in the kitchen during meal preparation. 

Environmental swabs may include utensils, cutting boards, sink, dish cloths or sponges, tap 

handles, refrigerator handles, door handle, and drawer pulls. Surface samplers recorded 

sample information on sample collection forms (see the Attachment), and they were trained 

and their technique examined 1 week before samples were taken. 

Samplers did not touch/clean/disinfect surfaces before they took the swab samples. Sterile, 

disposable templates of a 100 cm2 area were placed on flat surfaces to be swabbed and 

disposed of after a single use. Samplers swabbed irregularly shaped surfaces (e.g., utensil 

handles) over the entirety of the surface. While wearing gloves, samplers pressed the swab 

head against the surface of its container to release excess moisture and rubbed it slowly 

and thoroughly over the target area one time, reversing direction with each stroke. This 

procedure was repeated twice using different swabbing directions for each replicate. The 

swab was deposited back in the broth and sealed and was placed on cold packs for 

transportation. Samplers wore a new pair of gloves each time they took a swab. 

Wearing clean gloves, samplers transferred 25g lettuce samples from test kitchen 

containers to numbered Ziploc bags for transport. We provided participants with no more 

than 100g of lettuce to prepare the RTE salad. Lettuce samples were kept on cold packs 

during transportation to the NCSU laboratory. We stored swabs and lettuce samples at 4°C 

and processed them for microbial nucleic acid extraction (Section F.6) within 48 hours of 

collection. 

F.5 Elution and Concentration of MS2 from Lettuce Samples 

We eluted MS2 from lettuce samples as described by Gentry-Shields and Jaykus (2015) with 

a few modifications to optimize extraction. Briefly, we placed 25g from each lettuce sample 

taken from salads prepared in the test kitchen in polypropylene bags containing a filter 

9 The order in which the participants prepare the two foods was not specified, so some participants 

may have prepared the burgers first, and some may have prepared the salad first. 

F-2 
 

 

 

Appendix F: Microbiological Methods 

compartment and soaked them with 20 ml elution buffer (Tris-HCl 0.1 M, glycine 0.05 M, 

beef extract 3%, pH 9.5). We stomached the sample for 1 minute at 230 rpm using a 

stomacher. We removed the rinse fluid via the filter compartment of the bag to a 50 ml 

centrifuge tube and adjusted it to pH 7.0 ± 0.5 with 0.1 M HCl. 

We concentrated the MS2 from the lettuce eluates using PEG precipitation. The eluates of 

approximately 20 ml volume were subjected to precipitation with the addition of PEG MW 

8000 and NaCl in a final concentration of 12% (w/v) and 5%, respectively. We incubated 

the samples on a shaking platform at 4°C for at least 2 hours and centrifuged them at 8,500 

rpm for 20 minutes at 4°C. The pellet was suspended in 1 ml of PBS and stored at −20°C.

To remove residual inhibitory substances, we further subjected the virus concentrates to a 

chloroform:butanol purification step. Briefly, we treated 1 ml of the suspended pellet with 

one volume of chloroform:butanol (1:1, v/v) and vortexed the mixture for 2 minutes at 

room temperature and centrifuged it again at 12,000 rpm for 20 minutes. We isolated and 

stored the aqueous phase (supernatant) at −80°C until RNA extraction and RT-qPCR were 

performed as described in Section F.6. 

F.6 RNA Extraction and Detection of MS2 Bacteriophage by 

RT-qPCR 

We performed RNA extraction and detection of bacteriophage MS2 as described by GentryShields and Jaykus (2015). We performed extraction of MS2 RNA from 1 ml swab buffer and 

MS2 concentrated from lettuce samples using the automated bioMérieux NucliSENS 

easyMAG system, as per the manufacturer’s instructions. We then eluted the final purified 

RNA into 25 μl of proprietary buffer. RNA extracts were stored at −80°C until analysis by 

RT-qPCR. 

Table F-1 lists the primers and probe we used to detect MS2 (Conn, Habteselassie, 

Blackwood, & Noble, 2012). The probe was located at position 1689 in the MS2 coat protein 

gene MS2g2. The 25 μl RT-qPCR mixture consisted of 2.5 μl RNA, 400 nM of forward and 

reverse primers, 200 nM of fluorescently labeled TaqMan probe, 12.5 μl 2 μ reaction buffer 

(SuperScript III One-Step qRT-PCR Kit, Invitrogen), and 0.5 μl RT/Platinum Taq Mix. The 

reaction mixture was subjected to a one-step thermal cycling profile using a CFX96 Touch 

Real Time PCR Detection System from Bio-Rad under the following amplification conditions: 

(1) reverse transcription for 30 minutes at 50°C, (2) initial denaturation for 15 minutes at 

95°C, and (3) 45 cycles of 15 seconds at 95°C and 30 seconds at 60°C. We calculated 

bacteriophage MS2 concentration by comparing it to standard curves produced as described 

in Section F.2 (see Figure F-1). 

F-3 
401 

35 • 

3,0, 

~S 

u 2,0, ;i••··· 

15 

10 

:5 

0 

11) 1 2 

... 

·······: ............... ~ ........... ····: .... •···· .. •··: .............. . 

5 

loglO(copies) 

6 7 

• 

8, 9 

Meal Preparation Experiment Related to Thermometer Use 

Table F-1. Primers and Probe Identities, Sequences, and Genome Location for 

RT-qPCR Detection of Bacteriophage MS2 

Name Sequence (5′-3′) Location 

MS2qfor ATTCCGACTGCGAGCTTATT 1630 

MS2qrev TTCGACATGGGTAATCCTCA 1758 

MS2qProbe 6-FAM-ATTCCCTCAGCAATCGCAGCAAACT-BHQ1 1689 

Source: Conn et al. (2012). 

Figure F-1. Standard Curve MS2 Stock 

F.7 Sanitation of Test Kitchens Following Meal Preparation 

We sanitized the kitchens following meal preparation in accordance with NCSU’s guidelines 

for sanitizing laboratory work surfaces, a requirement of the University. We applied 

household bleach diluted to a 10% concentration to hard surfaces with a contact time of 60 

seconds before wiping them clean with a disposable paper towel. We repeated this step 

twice for a total of three sanitation steps. The efficacy of this sanitation procedure was 

confirmed during in-lab optimization studies and the pilot conducted in the test kitchen. All 

utensils, including knives, cutting boards, and bowls, for example, were cleaned in 

dishwashers. 

F-4 
Appendix F: Microbiological Methods 

ATTACHMENT 1 

SAMPLE COLLECTION FORM 

ID: _________________________ 

Date: ______________________ 

Sample collector: ___________ 

Sample Number Sample Type Irregular/Flat Time Taken 

Sanitation Validation 

0 Counter space Flat 

Utensils 

1 Knife handle Irregular 

2 Cutting board Flat 

3 Frying pan handle Irregular 

Cleaning Areas 

4 Inner sink surface Flat 

5 Dish cloth/sponge Irregular 

6 Tap handle Irregular 

7 Soap dispenser Irregular 

Kitchen Surfaces 

8 Refrigerator handle Irregular 

9 Spice containers Irregular 

10 Trash bin lid Irregular 

Other Surfaces 

11 Specify_______________________ 

12 Specify_______________________ 

Lettuce sample (from salad if prepared 

after burgers or garnish if salad 

prepared before burgers) 

F-5 

Appendix G: 

Observation Rubric 

To compare the food safety practices of primary meal preparers, we developed a decision 

tree to code actions using definitions from the U.S. Centers for Disease Control and 

Prevention’s contributing factors for foodborne illness, coupled with the World Health 

Organization’s (WHO’s) factors leading to foodborne illness (Bean, Goulding, Lao, & Angulo, 

1996; WHO, 2014). These definitions were supported by a review of scientific literature that 

focused on risky food safety practices (Anderson et al., 2004; Clayton & Griffith 2004; 

Green et al., 2006; Redmond et al., 2004). Definitions of food safety practices from the 

literature coupled with foodservice inspection criteria (FDA, 2013) led to the decision to 

focus the video observation methodology on capturing and cataloguing handwashing and 

cross-contamination incidents. 

We used notational analysis to record actions and their frequencies. Notational analysis is a 

generic tool used to collect observed events and place them in an ordered sequence 

(Hughes & Franks, 1997). Notational analysis has been used to track food safety behaviors, 

enabling the recording of specific details about events in the order in which they occur by 

associating a time stamp with those actions (Clayton & Griffith, 2004). Using a time stamp 

is especially useful when looking at sanitation steps limiting cross-contamination or the use 

of common food contact surfaces and equipment. Notational analysis has been used in 

consumer food safety behavior observations studies as well as participant foodservice 

observation (Clayton & Griffith, 2004; Green et al., 2006; Redmond et al., 2004). The study 

team developed action decision trees for handwashing (Figure G-1), direct crosscontamination (Figure G-2), indirect cross-contamination (Figure G-3), and thermometer 

usage (Figure G-4). 

G-1 
Not coded 

Not coded 

Contaminated hands? 

Handwashing attempt? 

All elements c ) - Correct Touched 

Equipment or RTE food? How were hands washed? 

Incorrect 

Some elements 

] Equipment 

: Used by other(s)? 

What was touched? 

Direct crosscontamination RTE foods 

Meal Preparation Experiment Related to Thermometer Use 

Figure G-1. Handwashing Action Decision Tree 

Contaminated hands: Hands that have come into contact with potentially contaminated material (raw 

food, contaminated equipment, touching of face or other parts of body or clothing) and that have 

not been washed according to CDC’s recommended guidelines for proper handwashing. 

▪ Elements of handwashing: 

▪ Wet your hands with clean, running water (warm or cold), turn off the tap, and apply 

soap. 

▪ Lather your hands by rubbing them together with the soap. Be sure to lather the 

backs of your hands, between your fingers, and under your nails. 

▪ Scrub your hands for at least 20 seconds. 

▪ Rinse your hands well under clean, running water. 

▪ Dry your hands using a clean towel or air dry them. 

https://www.cdc.gov/handwashing/when-how-handwashing.html 

G-2 
No 

Raw, potentially 

contaminated food? 

Yes 

[..__Not c-oded J Does it touch/drip on 

RTE food 

No 

[..__Not c-OOed J 

Yes 

Direct 

cross-contamination 

Appendix G: Observation Rubric 

Figure G-2. Direct Cross-Contamination Action Decision Tree 

Raw, potentially contaminated food: Food that may contain harmful bacteria that can cause illness due 

to lack of a cooking step or coming into contact with a contaminated surface. 

G-3 
Not coded 

Contaminated 

equipment? 

Was it cleaned before next 

use? 

Not coded What touched it next? 

Not coded 

To contaminated hands 

tree 

Hands 

Indirect crosscontamination 

Meal Preparation Experiment Related to Thermometer Use 

Figure G-3. Indirect Cross-Contamination Action Decision Tree 

Contaminated equipment: Equipment that has come into contact with potentially contaminated food or 

another potentially contaminated surface and that has not been properly washed and sanitized. 

Was it cleaned before next use? 

All surfaces and components of equipment are washed using running water and soap. 

G-4 
Food requires temperature 

verification for safety 

~ ------"----- ~ ~ ~-----------~ 

[ Nol wded J Was a th~o~le'"sed? 

Subjective doneness indicator 

obviously used 

Temperature recorded by 

thermometer. Is temperature less 

than FSIS recommendation 

Appendix G: Observation Rubric 

Figure G-4. Thermometer Use Decision Tree 

G-5 
RTI Project Number 

0215472 

Food Safety Consumer Research 

Project: Meal Preparation Experiment 

Related to Thermometer Use 

Addendum to Final Report: 

Microbiological Analysis 

August 28, 2018 

Prepared for 

Chris Bernstein 

USDA, FSIS, OPACE, 

Food Safety Education Staff 

1400 Independence Ave., S.W. 

Washington, DC 20250-3700 

Prepared by 

Sheryl C. Cates 

Ellen Thomas 

Katherine Kosa 

RTI International 

3040 E. Cornwallis Road 

Research Triangle Park, NC 27709 

Benjamin Chapman 

Lisa Shelley 

Rebecca M. Goulter 

Minh Duong 

Margaret Kirchner 

Lydia Goodson 

Savana Everhart 

Lindsay Doring 

Lee-Ann Jaykus 

North Carolina State University 

Raleigh, NC 27695 

Contents 

Section Page 

1. Introduction 1 

2. Methods 1 

2.1 Environmental Sampling ..............................................................................1 

2.2 MS2 Detection and Analysis..........................................................................1 

3. Results 1 

3.1 Prevalence .................................................................................................1 

3.2 Level of Contamination ................................................................................3 

3.3 Sink vs. Dishwasher ....................................................................................5 

3.4 Treatment vs. Control..................................................................................6 

3.5 Discretionary Samples .................................................................................7 

4. Implications 9 

4.1 Spice Containers .........................................................................................9 

4.2 Cross-Contamination and Handwashing .........................................................9 

5. References 9 

iii 
Tables 

Number Page 

1. Prevalence of Contamination and Level of Contamination of MS2 for Sampled 

Surfaces .........................................................................................................2 

2. Significant Differences in Levels of Contamination of MS2 Among Surfaces 

Sampled .........................................................................................................4 

3. Prevalence of Contamination and Level of Contamination of MS2 for the 

Kitchen Utensils Based on Washing Technique .....................................................6 

4. Types of Discretionary Surfaces Sampled ............................................................7 

5. Prevalence of Contamination and Level of Contamination for the Discretionary 

Samples..........................................................................................................8 

iv 
1. Introduction 

This report is an addendum to the Food Safety Consumer Research project final report. The 

report provides the results of the microbiological analysis for all of the locations sampled 

throughout the kitchen. 

2. Methods 

The final report describes the study design, selection of MS2 as a tracer organism, and 

inoculation of the turkey patties; therefore, this information is not included in this 

addendum. Additional information on the sampling technique and the detection method is 

provided below. 

2.1 Environmental Sampling 

Trained sample collectors used sponge sticks from 3M to complete the environmental 

sampling. Fourteen samples were taken for each observation: 1 as a cleaning control before 

the participant started cooking, 1 lettuce sample, 10 kitchen surfaces, and 2 discretionary 

samples based on triggers noted during the observation. Among the 10 kitchen surface 

samples taken, there were three types of surfaces: utensils, cleaning areas, and general 

kitchen surfaces. A 100 cm2 template was used for sample collection on flat surfaces, and 

the entirety of the surface was sampled for irregularly shaped surfaces. 

2.2 MS2 Detection and Analysis 

As described in the final report, MS2 was detected using a four-step protocol: concentration, 

purification, RNA extraction, and RT-qPCR (Dawson et al., 2005; Jones et al., 2012; 

Turgeon et al., 2014). A sample with log 5 MS2 genome units or greater was considered a 

positive result. Statistical analyses of the results using t tests and ANOVAs were completed 

in R, and 371 samples were used for all analyses unless otherwise noted. 

3. Results 

3.1 Prevalence 

MS2 was detected on all surfaces sampled in the study, but the prevalence varied by type of 

surface and ranged from 6.4 to 48.8% (see Table 1). For most of the surfaces sampled, the 

prevalence was between 12 and 22% with a few exceptions. Spice containers had the 

highest prevalence: nearly half of the samples were contaminated with MS2 (48.8%). Based 

on coding of the observations, it appeared that hands spread the MS2 from the turkey 

patties to the spice containers, which could account for the high prevalence of positive spice 

containers. Conversely, the refrigerator handle, inner sink surface, and knife handle were 

positive less than 8% of the time. Of the possible 371 inner sink surface samples and knife 

1 
Addendum: Meal Preparation Experiment Related to Thermometer Use 

handle samples, only the first 219 were processed because of their extremely low 

prevalence (below 10%). All 371 of the refrigerator door handle samples were processed 

and still yielded a low prevalence overall. 

Table 1. Prevalence of Contamination and Level of Contamination of MS2 for 

Sampled Surfaces 

Surface All Participants Treatment Control p valuea 

Knife handleb Prevalence contaminated, 

% (n) 

6.42 (218) 4.37 (108) 9.09 (110) .1659 

Level of contamination 

± SD, log genome 

copiesc

/handle (n) 

5.53 ± 0.64 (14) 5.52 ± 0.43 (4) 5.54 ± 0.73 (10) 

Cutting boardb Prevalence contaminated, 

% (n) 

12.70 (370) 11.11 (171) 14.07 (199) .3946 

Level of contamination 

± SD, log genome copies/ 

board (n) 

6.12 ± 0.96 (47) 6.13 ± 1.02 (29) 6.11 ± 0.94 (28) 

Frying pan/ 

George 

Foreman (GF) 

handleb 

Prevalence contaminated, 

% (n) 

Level of contamination 

± SD, log genome 

copies/handle (n) 

18.38 (370) 

5.69 ± 0.67 (68) 

17.54 (171) 

5.71 ± 0.71 (30) 

19.10 (199) 

5.69 ± 0.64 (38) 

.6997 

Inner sink 

surface 

Prevalence contaminated, 

% (n) 

6.39 (219) 5.50 (109) 7.27 (110) .5931 

Level of contamination 

± SD, log genome 

copies/surface (n) 

5.56 ± 0.47 (14) 5.61 ± 0.42 (6) 5.52 ± 0.53 (8) 

Dishcloth/ 

sponge 

Prevalence contaminated, 

% (n) 

18.33 (371) 17.44 (172) 19.10 (199) .6807 

Level of contamination 

± SD, log genome copies/ 

surface (n) 

5.49 ± 0.47 (68) 5.43 ± 0.40 (30) 5.54 ± 0.52 (38) 

Tap/faucet 

handle 

Prevalence contaminated, 

% (n) 

12.13 (371) 13.37 (172) 11.06 (199) .4939 

Level of contamination 

± SD, log genome copies/ 

handle (n) 

5.47 ± 0.52 (45) 5.44 ± 0.56 (23) 5.51 ± 0.47 (22) 

Soap dispenser Prevalence contaminated, 

% (n) 

22.37 (371) 22.67 (172) 22.11 (199) .8974 

Level of contamination 

± SD, log genome copies/ 

surface (n) 

5.70 ± 0.50 (83) 5.89 ± 0.53 (39) 5.53 ± 0.41 (44) 

Refrigerator 

door handle 

Prevalence contaminated, 

% (n) 

8.09 (371) 5.23 (172) 10.55 (199) .0615 

Level of contamination 

± SD, log genome copies/ 

handle (n) 

5.50 ± 0.37 (30) 5.51± 0.34 (9) 5.47 ± 0.38 (21) 

(continued) 

2 
Addendum: Meal Preparation Experiment Related to Thermometer Use 

Table 1. Prevalence of Contamination and Level of Contamination of MS2 for 

Sampled Surfaces (continued) 

Surface All Participants Treatment Control p valuea 

Spice Prevalence contaminated, 48.79 (371) 49.42 (172) 48.24 (199) .8139 

containers % (n) 

Level of contamination 6.18 ± 0.82 (181) 6.07 ± 0.78 (85) 6.28 ± 0.83 (96) 

± SD, log genome 

copies/surface (n) 

Trash bin lid Prevalence contaminated, 12.94 (371) 13.95 (172) 12.06 (199) .5891 

% (n) 

Level of contamination 5.89 ± 0.71 (48) 6.06 ± 0.82 (24) 5.72 ± 0.56 (24) 

± SD, log genome 

copies/surface (n) 

Discretionary Prevalence contaminated, 17.12 (742) 15.83 (344) 19.10 (398) .2751 

samples % (n) 

Level of contamination 5.72 ± 0.64 (127) 5.73 ± 0.60 (51) 5.72 ± 0.67 (76) 

± SD, log genome 

copies/handle (n) 

Notes: A positive result was one within 5 logs of the total inoculum (approximately log 10). We would not expect 

contamination levels of pathogens in USDA-regulated food products to exceed log 5, in step with data-supported 

assumptions found in 9 CFR Parts 301, 317, 318, 320, and 381. 

(n) = number of samples used in the analysis; SD = standard deviation. a We calculated p value significance testing using a chi-squared test for prevalence and repeated measures of 

analysis of variance (i.e., ANOVA) for level of contamination for the difference between the control and treatment 

groups. b A genome copy is the RT-qPCR equivalent of one bacteriophage particle, as calculated using a standard curve 

generated from a sample with known genome copy concentration as described in Appendix F of the final report. c For the three utensils—the knife handle, cutting board, and the frying pan/GF handle—results are provided for 

items washed in the sink and those placed in the dishwasher (i.e., may receive further cleaning and disinfection). 

Results by where the item was placed are presented and described below. 

Source: 2017 meal preparation experiment—microbiological samples. 

3.2 Level of Contamination 

Just as the prevalence of MS2 varied by surface, the level of MS2 contamination also varied 

depending on the surface sampled (see Table 2). The sampled utensils and kitchen surfaces 

had significantly higher levels of MS2 than the sampled cleaning areas. The lower MS2 

levels on the cleaning areas may be because cleaning areas often have more water running 

over them, cleaning areas may be touched more frequently, and soap is more likely to be 

present on these surfaces. All of these factors could reduce the number of microbes on a 

surface and are not as likely to be a factor with utensils and general kitchen surfaces. The 

level of MS2 contamination on kitchen surfaces was significantly higher than the level of 

MS2 contamination for the discretionary samples. This finding was not expected because the 

discretionary samples were selected by observers as likely to have a high level of MS2. To 

investigate this further the log genome copies were examined by individual sample surfaces 

as described below. 

3 
Addendum: Meal Preparation Experiment Related to Thermometer Use 

Table 2. Significant Differences in Levels of Contamination of MS2 Among 

Surfaces Sampled Knife Handle Cutting Boards

Frying Pan/GF HandleInner SinkSurfaceDishcloth/SpongeTap/FaucetHandleSoap DispenserRefrigeratorDoor Handle SpiceContainersTrash Bin Lid 

Knife handle 

Cutting boards 

Frying pan/GF 

handle 

Inner sink 

surface 

Dishcloth/ 

Sponge 

Tap/faucet 

handle 

Soap dispenser 

Refrigerator 

door handle 

Spice 

containers 

Trash bin lid 

.0063 

.0099 <.0001 <.0001 .0081 .0010 

.0099 <.0001 

.0119 

<.0001 <.0001 .0104 

<.0001 <.0001 .0230 

.0081 <.0001 

.0010 <.0001 

.0063 <.0001 .0119 <.0001 <.0001 <.0001 <.0001 

.0104 .0230 

Notes: The knife handle, cutting boards, and frying pan/GF handle are considered utensils. The inner sink surface, 

dishcloth/sponge, tap/faucet handle, and the soap dispenser are considered cleaning areas. The refrigerator door 

handle, spice containers, and trash bin lid are considered kitchen surfaces. 

Significance among the samples is shown on a grid view with each sample compared with all others. Readers 

should find the first sample they want to look at using the rows and the sample they want to compare it with 

using the columns. Where the row and column meet is the p value for the level of contamination. 

The p values are indicated as follows: black = a sample being compared with itself, grey = a p value of >.05, white 

= p values < 0.05. 

The two samples with the highest average genome units per gram were the spice containers 

and the cutting boards, with 6.18 and 6.12 average log genome units, respectively 

(Table 1). This means that, on average, millions of MS2 particles were detected on these 

surfaces. The spice containers also had the highest prevalence of MS2. This could be due to 

some of the same factors that were discussed previously regarding the high prevalence of 

MS2 on spice containers, most notably participants’ direct handling of the containers using 

their contaminated hands. Additionally, study participants did not routinely clean the spice 

containers like they did other surfaces such as the countertop (although all surfaces 

including the spice containers were cleaned and sanitized by study team members after 

each participant). Spice containers are also not necessarily touched as often as other 

kitchen supplies and are frequently stored on the counter. 

4 
Addendum: Meal Preparation Experiment Related to Thermometer Use 

As previously noted, not all samples were of the same surface area. A knife handle has an 

inherently different surface area than a tap/faucet handle, but because of the irregular 

surface area, the whole knife handle was sampled. A 100 cm2 template was used to sample 

flat surfaces. All results are provided as MS2 per surface swabbed (the entire surface area 

of an irregular object or 100 cm2 of a flat surface). The larger surface area sampled for 

some samples may contribute to having a higher MS2 load than other sampled surfaces. 

However, there is little that could be done to control for the variability in surface area 

sampled while still being true to the nature of a typical consumer kitchen. 

As shown in Table 2, there were significant differences in levels of contamination of MS2 

among the types of surfaces sampled. Using a one-way ANOVA, we found that most of the 

significant differences were driven by the high level of MS2 found on the spice containers. 

All surfaces sampled, except for the cutting boards and the trash bin lid—the surfaces with 

the second and third highest MS2 levels, respectively—had a significantly lower level of MS2 

compared with the spice containers. To further demonstrate the significant differences 

observed for spice containers, only five of the other nine surfaces sampled had 

contamination levels significantly lower than the cutting board, while seven of the other nine 

surfaces were significantly lower than the spice containers. The only other significant 

differences were between the trash bin and the dish cloth/sponge and between the 

tap/faucet handle and the trash bin lid. 

3.3 Sink vs. Dishwasher 

Kitchen utensils are often washed after they are used to prepare a meal but washing 

techniques can differ among consumers. To account for this, participants were instructed to 

either wash their utensils in the sink or leave them in the dishwasher based on whatever 

method they typically use at home. These utensils were then sampled and marked as a 

“sink” or “dishwasher.” The rationale was that participants who rely on dishwashers to clean 

and sanitize their kitchen utensils may be more likely to have microbes present from crosscontamination on kitchen utensils than those who rely on washing utensils manually in the 

sink. Analysis was conducted on the three utensils—the knife handle, cutting board, and the 

frying pan handle—to determine if there were any differences between the prevalence or 

level of MS2 on samples washed in the sink versus those placed in the dishwasher. 

The prevalence of MS2 varied by sample type but was highest on the frying pan/GF handle 

compared with the knife handle and cutting board samples. Sampled cutting boards and 

frying pan/GF handles placed in the dishwasher had significantly higher MS2 prevalence 

than those placed in the sink (see Table 3). A similar result was not observed for the 

sampled knife handles; this utensil had the lowest number of samples, the smallest surface 

area, and the lowest MS2 prevalence overall among the three types of utensils. The level of 

contamination for all three types of utensils was comparable regardless of whether the 

utensil was placed in the dishwasher or sink, and the highest MS2 levels were found for 

5 
Addendum: Meal Preparation Experiment Related to Thermometer Use 

sampled cutting boards (the second highest surface level of MS2 for all sampled areas). 

There were no significant differences in the level of contamination (results not shown). 

Table 3. Prevalence of Contamination and Level of Contamination of MS2 for the 

Kitchen Utensils Based on Washing Technique 

Utensil All Samples Dishwasher Sink p valuea 

Knife 

handleb 

Prevalence contaminated 

% (n) 

Level of contamination 

± SD, log genome 

copiesc

/handle (n) 

5.52 (181) 

5.39 ± 0.47 (10) 

8.82 (34) 

5.16 ± 0.15 (3) 

4.76 (147) 

5.50 ± 0.31 (7) 

.3516 

Cutting 

boardb 

Prevalence contaminated, 

% (n) 

Level of contamination 

± SD, log genome 

copies/board (n) 

13.08 (321) 

6.22 ± 1.00 (42) 

22.58 (62) 

6.98 ± 0.98 (14) 

10.81 (259) 

5.83 ± 0.72 (28) 

.0137 

Frying 

pan/GF 

handle 

Prevalence contaminated, 

% (n) 

Level of contamination 

± SD, log genome 

copies/handle (n) 

19.50 (323) 

5.62 ± 1.00 (63) 

35.09 (57) 

5.80 ± 0.82 (20) 

16.17 (266) 

5.53 ± 1.07 (43) 

.0011 

Notes: A positive result was one within 5 logs of the total inoculum (approximately log 10). We would not expect 

contamination levels of pathogens in USDA-regulated food products to exceed log 5, in step with data-supported 

assumptions found in 9 CFR Parts 301, 317, 318, 320, and 381. 

(n) = number of samples used in the analysis; SD = standard deviation. 

a We calculated p value significance testing using a chi-squared test for prevalence and repeated measures of 

analysis of variance (i.e., ANOVA) for level of contamination for the difference between utensils placed in the 

sink vs. placed in the dishwasher. 

b Observations in which multiple cutting boards or knives were used or the video was not available were excluded 

from the analysis. For knife handles, the number of observations analyzed was 181 because of a low frequency 

of positive results in the first 56% of observations. After this point, we stopped processing these samples. 

c A genome copy is the RT-qPCR equivalent of one bacteriophage particle, as calculated using a standard curve 

generated from a sample with known genome copy concentration as described in Appendix F of the final report. 

Source: 2017 meal preparation experiment—microbiological samples. 

3.4 Treatment vs. Control 

The primary purpose of this study was to evaluate the impact of a USDA food safety video 

on thermometer use.1 The treatment group was exposed to the video, while the control 

group was not. The impact of the video on food thermometer use was described in the final 

report, but the microbiological results were not fully described. For all analyses conducted, 

there were no significant differences seen between the treatment group and the control 

group (Table 2 and other data not shown). The refrigerator door handle was contaminated 

less frequently in the treatment group (approximately 5% of the time) compared with the 

1 “The Importance of Cooking to a Safe Internal Temperature and How to Use a Food Thermometer, 

https://www.youtube.com/watch?v=-2KkV2yFiN0 

6 
Addendum: Meal Preparation Experiment Related to Thermometer Use 

control group (approximately 11% of the time); however, this difference was not significant 

(p = .0615). The lack of statistically significant differences between the treatment and 

control groups suggests that making consumers aware of and changing one food safety 

behavior like thermometer use does not necessarily carry over to other food safety 

behaviors like avoiding cross-contamination. 

3.5 Discretionary Samples 

The discretionary samples varied for each observation but can be categorized into five 

general categories as shown in Table 4: cupboard, drawers, and counters; participant items; 

kitchen tools; cleaning supplies and cloths; and oven, GF, and microwave surfaces. The 

prevalence of MS2 for the discretionary samples varied by type of surface and ranged from 

6.7 to 24.7% (see Table 5). The results for prevalence of MS2 were as expected compared 

with those presented in Table 1 for nondiscretionary samples. Likewise, the results for 

average log genome copies of MS2 (i.e., levels) were consistent with those presented in 

Table 1. The results were within the 5 log range, and there were no significant differences 

among the surfaces. These findings suggest that the discretionary surfaces were 

contaminated at a similar frequency and level as other kitchen surfaces with some variation 

across different surfaces; however, these differences were not statistically significant. (e.g., 

kitchen tools and participant items had a different prevalence and level of contamination). 

There was no significant differences between treatment and control for prevalence or level 

among the discretionary samples. 

Table 4. Types of Discretionary Surfaces Sampled 

Cupboards, 

Drawers, 

Counters 

Participant 

Items 

Kitchen 

Tools 

Cleaning 

Supplies and 

Cloths 

Oven, GF, 

and 

Microwave 

Examples Cupboard Cell phone Measuring 

spoons 

Dish soap 

bottle 

GF top 

Countertop Coffee cup Spatula Apron Stove knobs 

Drawer Earbuds Mixing bowl Paper towel 

holder 

Microwave 

door 

Cabinet knobs Water bottle Tongs Sink sprayer Stove surface 

Table surface Glasses Recipe card Dishcloth GF cord 

Total sampled 176 89 231 76 170 

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Addendum: Meal Preparation Experiment Related to Thermometer Use 

Table 5. Prevalence of Contamination and Level of Contamination for the 

Discretionary Samples 

Location All Participants Treatment Control p valuea 

Cupboards, Prevalence contaminated 13.64 (176) 15.12 (86) 12.22 (90) .5763 

drawers, % (n) 

counters 

Level of contamination 5.67 ± 0.59 (24) 5.54 ± 0.44 (13) 5.27 ± 1.87 (11) 

± SD, log genome 

copiesb/handle (n) 

Participant items Prevalence contaminated, 6.74 (89) 2.33 (43) 10.87 (46) .2794 

% (n) 

Level of contamination ± 5.73 ± 0.79 (7) 6.11 (2) 5.54 ± 0.38 (5) 

SD, log genome copies/ 

board (n) 

Kitchen tools Prevalence contaminated, 17.75 (231) 12.75 (102) 13.95 (129) .7909 

% (n) 

Level of contamination 5.91 ± 0.74 (41) 5.93 ± 0.84 (13) 5.84 ± 0.62 (18) 

± SD, log genome copies/ 

handle (n) 

Cleaning Prevalence contaminated, 18.42 (76) 11.43 (35) 24.39 (41) .1490 

supplies and % (n) 

cloths 

Level of contamination 5.57 ± 0.53 (14) 5.69 ± 0.50 (4) 5.58 ± 0.57 (10) 

± SD, log genome copies/ 

surface (n) 

Oven, GF, and Prevalence contaminated, 24.71 (170) 19.73 (76) 27.70 (94) .2287 

microwave % (n) 

Level of contamination 5.61 ± 0.55 (42) 5.84 ± 0.71 (15) 5.50 ± 0.40 (26) 

± SD, log genome copies/ 

surface (n) 

a We calculated p value significance testing using a chi-squared test for prevalence and repeated measures of 

analysis of variance (i.e., ANOVA) for level of contamination for the difference between treatment and control 

groups. 

b A genome copy is the RT-qPCR equivalent of one bacteriophage particle, as calculated using a standard curve 

generated from a sample with known genome copy concentration as described in Appendix F of the final report. 

Source: 2017 meal preparation experiment—microbiological samples. 

8 
Addendum: Meal Preparation Experiment Related to Thermometer Use 

4. Implications 

4.1 Spice Containers 

Of the kitchen surfaces sampled in this study, the spice containers were the most frequently 

positive for MS2. This finding was not expected because previous studies have not sampled 

spice containers when evaluating cross-contamination. Before FSIS’ July 2018 media 

campaign presenting the results of this study, food safety messaging on the handling of 

spice containers and their role in consumer kitchen cross-contamination was not available. 

Because of the high levels and prevalence of MS2 on spice containers demonstrated in this 

study, we recommend that food safety educators develop and test messaging focused on 

the storage of spices and disinfection of spice containers. Messages could emphasize storing 

the containers in a cupboard instead of on the countertop and disinfecting the containers 

after use to prevent cross-contamination. If stored on the counter, the containers may be 

more likely to come into contact with raw meats and participants may not wash their hands 

before handling them. 

4.2 Cross-Contamination and Handwashing 

Among all the surfaces sampled, about 81% of participants had at least one quantifiable 

positive cross-contamination event during meal preparation. The final report provides the 

results for handwashing compliance, so those results are not repeated here. The 

observational data suggest that failure to wash hands correctly is a major factor leading to 

cross-contamination in consumer kitchens. As previously noted, significant differences in the 

microbiological results were not found between the treatment and control groups, 

suggesting that making consumers aware of changing one food safety behavior like 

thermometer use does not necessarily carry over to other food safety behaviors like 

avoiding cross-contamination. To affect consumer practices that result in crosscontamination, direct messaging is also needed on proper handwashing and practices to 

avoid cross-contamination. 

5. References 

Dawson, D. J., Paish, A., Staffell, L. M., Seymour, I. J., & Appleton, H. (2005). Survival of 

viruses on fresh produce, using MS2 as a surrogate for norovirus. Journal of Applied 

Microbiology, 98(1), 203–209. 

Jones, T. H., Muehlhauser, V., & Croken, G. (2012). Development of an optimized method 

for the recovery of infectious F-RNA coliphage MS2 from meat. Journal of Virological 

Methods, 185(1), 69–73. 

Turgeon, N., Toulouse, M. J., Martel, B., Moineau, S., & Duchaine, C. (2014). Comparison of 

five bacteriophages as models for viral aerosols studies. Applied and Environmental 

Microbiology, 80(14), 4242–50. 

9