Results of Data Analysis for the Listeria 

monocytogenes RLm Risk-based Sampling 

Program, April 2006 through December 2007 

Stephen W. Mamber, USDA 

Kristina Barlow, USDA 

Kim Green, USDA 

January 2009 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

ACKNOWLEDGEMENTS 

This report is the result of efforts and contributions from across the Food Safety and Inspection Service. 

The Data Analysis and Integration Group (DAIG) of the Office of Food Defense and Emergency 

Response developed this report in consultation with experts from other program areas, including 

Headquarters and field personnel. Key contributions were made by the following individuals: 

Nelson Clinch 

Erin Dreyling 

Ron Eckel 

Emilio Esteban 

Peter Evans 

Reem Ghoneim 

Gail Graves 

Susan Knower 

David LaBarre 

Loren Lange 

Priscilla Levine 

Evelyne Mbandi 

Supriya Shah 

Theresa Taylor 

Paul Uhler 

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Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

TABLE OF CONTENTS 

Acknowledgements ........................................................................................................................ i

Table of Contents.......................................................................................................................... ii

List of Figures...............................................................................................................................iii

List of Tables................................................................................................................................ iv

Acronyms and Abbreviations..................................................................................................... vi

Executive Summary...................................................................................................................... 1

1. Introduction.......................................................................................................................... 2

1.1 Background ................................................................................................................. 3

2. Data Collection Design and Implementation..................................................................... 5

3. Data Analysis Procedures.................................................................................................... 6

4. Results and Discussion......................................................................................................... 7

4.1 RLm Testing Results for April through December 2006 ............................................ 7

4.2 RLm Testing Results for Calendar Year 2007 .......................................................... 11

4.3 Classification of Lm-Positive Samples, April 2006 through December 2007 .......... 14

4.4 Types and Sources of Lm-Positive Samples, April 2006 through December 2007 .. 15

4.5 Isolate Subtyping Results.......................................................................................... 18

4.6 Results Based on Alternatives Used to Control L. monocytogenes .......................... 20

4.7 Results by Establishment HACCP Size .................................................................... 21

4.8 Results by Food Product Category............................................................................ 21

4.9 Results by FSIS District ............................................................................................ 21

4.10 Results by Geographic Region.................................................................................. 22

4.11 Results by Season and Month ................................................................................... 22

4.12 Food Safety Assessment (FSA) Results.................................................................... 41

4.13 Trend Analysis of Combined RLm Data: April 2006 through December 2007 ....... 43

5. Summary and Conclusions................................................................................................ 48

Appendix A: FSIS Scheduling Criteria for Routine Lm Risk-based (RLm) Sampling 

Program................................................................................................................. 51

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Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

LIST OF FIGURES 

Figure 4.1.1. Samples Collected and Tested for L. monocytogenes, April–December 2006 ..... 8

Figure 4.1.2. Number of Lm-Positive Samples, April–December 2006..................................... 8

Figure 4.1.3. Percentage of Lm-Positive Samples, April–December 2006 ................................ 9

Figure 4.1.4. Number of Establishments with Lm-Positive Samples, April–December 2006 . 10

Figure 4.1.5. Percentage of Establishments with Lm-Positive Samples, April–December 

2006 ..................................................................................................................... 10

Figure 4.2.1. Samples Collected and Tested for L. monocytogenes, Calendar Year 2007....... 11

Figure 4.2.2. Number of Lm-Positive Samples, Calendar Year 2007 ...................................... 12

Figure 4.2.3. Percentage of Lm-Positive Samples, Calendar Year 2007 .................................. 12

Figure 4.2.4. Number of Establishments with Lm-Positive Samples, Calendar Year 2007 ..... 13

Figure 4.2.5. Percentage of Establishments with Lm-Positive Samples, Calendar Year 2007. 14

Figure 4.6.1. Percentage of Lm-Positive Contact Surface Samples by Control Alternative, 

April–December 2006 ......................................................................................... 24

Figure 4.6.2. Percentage of Lm-Positive Environmental Samples by Control Alternative, 

April–December 2006 ......................................................................................... 24

Figure 4.6.3. Percentage of Lm-Positive Product Samples by Control Alternative, Calendar 

Year 2007 ............................................................................................................ 25

Figure 4.6.4. Percentage of Lm-Positive Contact Samples by Control Alternative, Calendar 

Year 2007 ............................................................................................................ 25

Figure 4.6.5. Percentage of Lm-Positive Environmental Samples by Control Alternative, 

Calendar Year 2007............................................................................................. 26

Figure 4.7.1. Percentage of Lm-Positive Contact Samples by Establishment Size, April–

December 2006.................................................................................................... 28

Figure 4.7.2. Percentage of Lm-Positive Environmental Samples by Establishment Size, 

April–December 2006 ......................................................................................... 28

Figure 4.7.3. Percentage of Lm Product Samples Establishment Size, Calendar Year 2007 ... 29

Figure 4.7.4. Percentage of Lm-Positive Contact Samples by Establishment Size, Calendar 

Year 2007 ............................................................................................................ 29

Figure 4.7.5. Percentage of Lm-Positive Environmental Samples by Establishment Size, 

Calendar Year 2007............................................................................................. 30

Figure 4.8.1. Percentage of Lm-Positive Samples by Food Product Category, April– 

December 2006.................................................................................................... 30

Figure 4.8.2. Percentage of Lm-Positive Samples by Food Product Category, Calendar Year 

2007 ..................................................................................................................... 31

Figure 4.9.1. Percentage of Lm-Positive Contact Surface Samples by FSIS District, April–

December 2006.................................................................................................... 34

Figure 4.9.2. Percentage of Lm-Positive Environmental Samples by FSIS District, April–

December 2006.................................................................................................... 34

Figure 4.9.3. Percentage of Lm-Positive Product Samples by FSIS District, Calendar Year 

2007 ..................................................................................................................... 35

Figure 4.9.4. Percentage of Lm-Positive Contact Samples by FSIS District, Calendar Year 

2007 ..................................................................................................................... 35

Figure 4.9.5. Percentage of Lm-Positive Environmental Samples by FSIS District, 

Calendar Year 2007............................................................................................. 36

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Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.10.1. Percentage of Lm-Positive Contact Surface Samples by Geographic Region, 

April–December 2006 ......................................................................................... 38

Figure 4.10.2. Percentage of Lm-Positive Environmental Samples by Geographic Region, 

April–December 2006 ......................................................................................... 38

Figure 4.10.3. Percentage of Lm-Positive Product Samples by Geographic Region, Calendar 

Year 2007 ............................................................................................................ 39

Figure 4.10.4. Percentage of Lm-Positive Contact Surface Samples by Geographic Region, 

Calendar Year 2007............................................................................................. 39

Figure 4.10.5. Percentage of Lm-Positive Environmental Samples by Geographic Region, 

Calendar Year 2007............................................................................................. 40

Figure 4.11.1. Percentage of Lm-Positive Samples by Season, April–December 2006 ............. 40

Figure 4.11.2. Percentage of Lm-Positive Samples by Season, Calendar Year 2007................. 41

Figure 4.11.3. Percentage of Lm-Positive Samples by Month, April–December 2006.............. 42

Figure 4.11.4. Percentage of Lm-Positive by Month, Calendar Year 2007................................ 42

Figure 4.13.1. Percentage of Total Samples Positive for L. monocytogenes, April 2006–

December 2007.................................................................................................... 44

Figure 4.13.2. Percentage of Product Samples Positive for L. monocytogenes, April 2006–

December 2007.................................................................................................... 44

Figure 4.13.3. Percentage of Contact Surface Samples Positive for L. monocytogenes, April 

2006–December 2007.......................................................................................... 45

Figure 4.13.4. Percentage of Environmental Samples Positive for L. monocytogenes, April 

2006–December 2007.......................................................................................... 45

Figure 4.13.5. Percentage of Establishments with at Least One Lm-Positive Sample 

(All Types), April 2006–December 2007............................................................ 46

Figure 4.13.6. Percentage of Establishments with Lm-Positive Product Samples, April 2006–

December 2007.................................................................................................... 46

Figure 4.13.7. Percentage of Establishments with Lm-Positive Contact Surface Samples, 

April 2006–December 2007 ................................................................................ 47

Figure 4.13.8. Percentage of Establishments with Lm-Positive Environmental Samples, 

April 2006–December 2007 ................................................................................ 47

LIST OF TABLES 

Table 4.1.1. Detection of L. monocytogenes in Product, Contact Surface, and Environmental 

Samples, April–December 2006............................................................................ 7

Table 4.1.2. Number and Percentage of Establishments with at Least One Lm-Positive 

Sample, April–December 2006 ............................................................................. 9

Table 4.2.1. Detection of L. monocytogenes in Product, Contact Surface, and Environmental 

Samples, Calendar Year 2007 ............................................................................. 11

Table 4.2.2. Number and Percentage of Establishments with at Least One Lm-Positive 

Sample, Calendar Year 2007............................................................................... 13

Table 4.3.1. Classification of Lm-Positive Samples from Establishments with at Least One 

Positive Sample ................................................................................................... 15

Table 4.4.1. Types of Lm-Positive Product Samples, April 2006–December 2007................ 15

Table 4.4.2. Types of Lm-Positive Contact Surface Samples, April 2006–December 2007 .. 16

iv 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Table 4.4.3. Lm-Positive Rate for the Main Types of Contact Surface Samples, 

April 2006–December 2007 ................................................................................ 16

Table 4.4.4. Types of Lm-Positive Environmental Samples, April 2006–December 2007 .... 17

Table 4.4.5. Positive Rate for the Types of Lm Environmental Samples, April 2006–

December 2007.................................................................................................... 17

Table 4.5.1. Patterns and Occurrence of L. monocytogenes PFGE Subtypes Isolated in the 

RLm Program, April 2006–December 2007 ....................................................... 19

Table 4.5.2. Incidence of Multiple Isolations of the Same PFGE Subtype within the Same 

Establishment, April 2006–December 2007 ....................................................... 20 

Table 4.6.1. Detection of L. monocytogenes by Control Alternative, April–December 2006 23

Table 4.6.2. Detection of L. monocytogenes by Control Alternative, Calendar Year 2007.... 23

Table 4.7.1. Detection of L. monocytogenes by Establishment Size, April–December 2006. 27

Table 4.7.2. Detection of L. monocytogenes by Establishment Size, Calendar Year 2007 .... 27

Table 4.9.1. Detection of L. monocytogenes by FSIS District, April–December 2006 .......... 32

Table 4.9.2. Detection of L. monocytogenes by FSIS District, Calendar Year 2007 .............. 33

Table 4.10.1. Detection of L. monocytogenes by Geographic Region, April–December 2006 37

Table 4.10.2. Detection of L. monocytogenes by Geographic Region, Calendar Year 2007.... 37

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Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

ACRONYMS AND ABBREVIATIONS 

CDC Centers for Disease Control and Prevention 

DAIG Data Analysis and Integration Group 

EIAO Enforcement, Investigations, and Analysis Officer 

FSA Food Safety Assessment 

FSIS Food Safety and Inspection Service 

GMP Good manufacturing practice 

HACCP Hazard Analysis and Critical Control Point 

IVT Intensified Verification Testing 

Lm L. monocytogenes 

LSFS Laboratory Sample Flow System 

NOIE Notices of Intended Enforcement 

NR Noncompliance Record 

OFO Office of Field Operations 

OSEL Outbreaks Section of the Eastern Laboratory Microbiology Branch 

PBIS Performance-based Inspection System 

PFGE Pulsed field gel electrophoresis 

PHV Public Health Veterinarian 

RLm Listeria monocytogenes Risk-based Sampling Program 

RTE Ready-to-eat 

USDA United States Department of Agriculture 

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Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

EXECUTIVE SUMMARY 

The Food Safety and Inspection Service’s (FSIS’s) Listeria monocytogenes Risk-based Sampling 

Program (RLm) program is designed to detect L. monocytogenes (Lm) contamination from food contact 

surfaces and noncontact environmental sources in addition to post-lethality environmentally exposed 

ready-to-eat (RTE) meat and poultry products. The Agency analyzed results of Lm testing of meat and 

poultry product, food contact surface, and environmental (nonfood contact) samples collected under the 

RLm sampling program for the period April 2006 through December 2007. The analyses, which included 

3,275 samples from 63 establishments in 2006 and 6,210 samples from 127 establishments in calendar 

year 2007, focused on 

• the incidence and categorization of positive Lm samples from sampled establishments; 

• types, sources, and pulsed field gel electrophoresis (PFGE) subtyping of Lm isolates from the 

positive samples; 

• descriptive summaries with respect to 

– Lm control alternatives employed by the establishment, 

– establishment HACCP (Hazard Analysis and Critical Control Point) size, 

– FSIS District, 

– geographic location of the establishment, and 

– season or month of sample collection; and 

• trends in percentage of positive results from 2006 to 2007. 

The Agency also conducted a limited evaluation of Food Safety Assessment (FSA) reports collected 

under the RLm program. 

Results indicate a low incidence of Lm-positive samples relative to the total numbers of samples collected 

in 2006 and 2007. Positive results ranged from 0 to 0.2% for product samples, from 0.2 to 0.4% for 

contact surface samples, and from 1.6 to 1.7% for environmental samples. Only two product samples 

from two separate establishments were positive for L. monocytogenes (both in calendar year 2007). In 

contrast, about 1 in 20 establishments had Lm-positive contact surface results, and about 1 in 5 

establishments had Lm-positive environmental samples. These results demonstrate the potential of the 

RLm sampling program in identifying establishments that may be at risk for L. monocytogenes. Drains, 

wheels, and floors or floor mats were the most common sources of positive environmental samples, while 

sources of contact surface contamination were varied. PFGE subtyping results yielded 41 distinct patterns 

among 69 isolates tested. However, only one matching PFGE subtype was obtained from the same 

establishment (a chicken salad wrap and a salad container). 

Results of analysis based on Lm control alternatives showed that most positive samples were obtained 

from establishments employing Lm control Alternative 2b (antimicrobial treatment/high-risk) and 

Alternative 3 (sanitation only/highest risk). These results were as expected because these alternatives are 

less stringent than the other alternatives. Most of the positive RLm samples were from establishments that 

produced deli meats and hot dogs. Positive environmental samples were obtained at all times of the year, 

whereas most of the positive contact surface samples were obtained in the summer and fall. Trends in the 

percentage of Lm-positive results from 2006 to 2007 showed slight changes for all types of testing. Once 

complete testing results are available for 2008, FSIS will conduct an expanded analysis to better evaluate 

the overall effectiveness of the RLm program over the 2006 through 2008 period. 

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Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

1. INTRODUCTION 

FSIS conducts regulatory microbiological testing of ready-to-eat (RTE) meat and poultry products for 

Listeria monocytogenes (Lm), Salmonella, and Escherichia coli O157:H7. In 2004, FSIS began risk-based 

testing of RTE products for L. monocytogenes. One of the first risk-based sampling and testing programs 

was ALLRTE (random verification sampling of all RTE meat and poultry products). All establishments 

were considered at equal risk under the ALLRTE sampling program. What made ALLRTE risk based was 

that inspectors were directed to collect meat and poultry product samples that were considered to be 

higher risk. Products considered to be of low risk were exempt from sampling and testing. FSIS 

regulations mandated the reporting of various production factors by establishments producing meat and 

poultry products that were exposed to the post-lethality production environment. This served as the basis 

for a sampling program based on the risk characteristics of the producing establishment and not just on 

product types. 

RTE001, a sampling and testing program for RTE products based on these establishment risk factors, was 

initiated in January 2005. An Lm risk-based sampling project named the Routine Lm Risk-based (RLm) 

Sampling Program then was introduced in April 2006. Whereas RTE001 involves sampling and testing of 

the RTE meat and poultry products themselves, the RLm project includes sampling and testing of 

products, product contact surfaces, and environmental surfaces. This makes the RLm program a proactive

sampling project, capable of identifying establishments with a higher risk of Lm contamination in the 

food processing environment before product contamination can actually be demonstrated. In addition, a 

Food Safety Assessment (FSA) is conducted at the establishment in conjunction with the sampling and 

testing. Furthermore, unlike the ALLRTE and RTE001 programs in which samples are also tested for 

Salmonella and E. coli O157:H7, in the risk-based RLm program, samples are collected and tested for L. 

monocytogenes only. 

The new RLm testing program consists of the following sampling projects: 

1. RLMPROD—the routine risk-based testing of intact RTE food product samples collected 

concurrently with food contact and environmental (nonfood contact) surface samples throughout 

the selected production shift. 

2. RLMCONT—the routine risk-based testing of surfaces that have direct contact with RTE product 

in the RTE production area (e.g., conveyor belts, cooler storage racks, luggers, slicers, peelers, 

loaders, table tops). 

3. RLMENVR—the routine risk-based testing of environmental (nonfood contact) surfaces in the 

RTE production areas (e.g., floors, drains, walls, air-vents, overhead structures). 

Samples collected under this program are limited to establishments subject to 9 CFR Part 430 (i.e., 

establishments in which RTE products are exposed to the post-lethality environment [see 

http://www.access.gpo.gov/nara/cfr/waisidx_08/9cfr430_08.html]). 

In accordance with FSIS Directive 10,240.5, EIAO Assessment of Compliance with the Lm Regulation 

and Lm Sampling Program, FSIS Enforcement, Investigations, and Analysis Officers (EIAOs) and Public 

Health Veterinarians (PHVs), trained in EIAO methodologies, are responsible for conducting RLm 

sampling and assessing whether the establishment’s food safety system complies with 9 CFR Part 430 

(see http://www.fsis.usda.gov/OPPDE/rdad/FSISDirectives/10240.5.pdf). 

The selection of establishments for food contact and environmental swab sampling and number of 

samples for testing follows an FSIS risk-based sampling algorithm. The risk-ranking algorithm is 

maintained using data from various Agency resources, including information from FSIS Form 10,240-1 

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Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

(in particular, food product category and sanitation alternative for controlling Listeria) and the 

establishment’s sample history. Once the algorithm generates its risk ranking, additional scheduling 

criteria are employed to select establishments for testing. Scheduling criteria for the RLm program for 

2007 are posted on the FSIS Web site and are included here as Appendix A. The risk ranking is updated 

monthly. Accordingly, each month, a scheduling memo is sent to districts to inform them of the 

establishments selected for RLm sample collection activity. 

FSIS tabulated, analyzed, evaluated, and reported on Lm data collected under the RLm program since its 

inception in April 2006 through calendar year 2007. Accordingly, the objectives of this report were to (1) 

obtain, tabulate, and review sampling results; (2) evaluate the data with respect to program effectiveness; 

and (3) identify possible trends in the data. 

1.1 Background 

The RLm program was initially conceived as a means of routinely collecting and testing three types of 

samples (food product, food contact surface, and environmental samples) in post-lethality exposed RTE 

production areas where L. monocytogenes may be present. The impetus for this sampling and testing 

effort was the need to determine if, or how well, establishments were controlling Lm contamination in 

post-lethality exposed RTE products based on regulation 9 CFR 430. FSAs are conducted in conjunction 

with sample testing to evaluate the food safety practices of establishments producing post-lethality 

exposed RTE products, particularly those establishments considered to be high risk. 

This examination of high-risk establishments on a routine basis was conceptually similar to that of 

Intensified Verification Testing (IVT) of food contact surface and environmental samples in response to 

samples tested positive for L. monocytogenes. What sets the RLm program apart from IVT (and indeed, 

from other FSIS sampling programs for foodborne pathogens) is that the routine testing of samples from 

food contact surfaces and processing environments is not done in response to positive product samples. 

Rather, the purpose of such testing is to proactively detect the presence of L. monocytogenes in 

establishments even in the absence of actual product contamination and to take corrective actions 

accordingly. (With respect to positive samples from the RLm program, one of these corrective actions is 

IVT itself, employed as a follow-up when a sample tests positive for L. monocytogenes.) 

In conducting the RLm program, FSIS anticipated it would be able to assess the compliance of 

establishments with regulation 9 CFR 430 regarding the control of L. monocytogenes in post-lethality 

exposed RTE production areas and help ensure that RTE products are safe for consumption at the end of 

the production process. With the RLm program in place, FSIS has the ability to verify and evaluate Lm

control alternatives and sanitation practices at individual establishments that would not be possible with 

normal day-to-day inspection. The RLm program was also designed in part to increase confidence in the 

effectiveness of a given establishment’s control measures and interventions (alternatives). 

RLm testing involves collecting multiple samples as a unit—3 product samples, 10 product contact 

samples, and 5 environmental (nonproduct contact) samples—during a production shift. This contrasts 

markedly with RTE001 and ALLRTE, in which a single RTE product sample is collected at a given point 

in time. 1 Moreover, because RLm sampling at each establishment is done in conjunction with an FSA, an 

in-depth evaluation of food safety practices is possible. The product, contact surface, and environmental 

 

1

 Initially, the numbers of 18-sample units used at each establishment were based on the number of production lines. Currently, 

the number of sampling units is based on establishment HACCP (Hazard Analysis and Critical Control Point) size, with three, 

two, and one sample units used at establishments classified as HACCP sizes large, small, and very small, respectively. This 

system provides for consistency with respect to the logistics of sample collection and testing. It should also be noted that the 

ratio of 10:5 for contact and environmental samples is because positive contact samples have defined regulatory consequences, 

which is not the case for positive environmental samples. 

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Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

sample data collected from the establishments can help identify possible risk factors that could be 

associated with positive results. For example, testing of food contact and environmental samples may 

permit the identification of establishments where there is evidence of control issues such as harborage 

(sites of Lm survival or persistence) or poor sanitation practices. 

Because the RLm program was intended to be a routine sampling program to complement the FSA 

process, FSIS has the expectation that establishments selected for sampling should be in compliance with 

all regulatory standards because those establishments are selected for sampling on the basis of risk rather 

than for any particular cause. Accordingly, FSIS evaluates establishments producing RTE products first 

and foremost to ensure the safety of these products and thus to protect the public from foodborne Listeria

infections. If a given establishment has positive results from the RLm sampling, FSIS takes enforcement 

actions as necessary to address product contamination and adulteration. Furthermore, the positive results 

serve as the impetus for focusing inspection efforts and intensifying inspection resources in that 

establishment. Such results may indicate poor HACCP design, execution, or both. In addition to 

determining the vulnerabilities and the adequacy of the establishment’s food safety practices with respect 

to L. monocytogenes, FSIS develops and implements policies to improve the effectiveness of the 

establishment’s Listeria contamination control practices. 

The Lm sampling algorithm used in the RLm sampling program has been designed to ensure the greatest 

probability of finding establishments with the highest public health risk with respect to Lm contamination. 

The risk-ranking algorithm considers the establishments that are most likely to have the greatest public 

health risk (that is, the potential to cause illness in the greatest number of consumers) based on the types 

and volumes of RTE products produced under the establishments’ stated contamination control and 

sanitation practices. It has been recognized that certain products, such as deli meats, present a public 

health risk because they are more likely to be contaminated if proper control and sanitation procedures are 

not used. 

The RLm risk-ranking algorithm is employed on a monthly basis to identify all the active establishments, 

rank them according to potential risk, and assign them a ranking by FSIS District for sampling after 

applying exclusion rules. In short, the risk-ranking algorithm uses several components to identify the 

highest-risk establishments with respect to detecting RTE meat and poultry products contaminated by L. 

monocytogenes. The ranking is influenced largely by sanitation control alternative and by product 

category (see FSIS Directive 10,240.5). However, the algorithm does not select the products to be 

sampled. Instead, the EIAO selects products based on which are considered to be the highest risk and 

selects appropriate contact and environmental surfaces. 

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Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

2. DATA COLLECTION DESIGN AND IMPLEMENTATION 

Data routinely generated from the RLm program were used for all analyses. FSIS tabulated the routine 

risk-based sample information for L. monocytogenes in RTE meat products that were collected in the 

FSIS 10240-1 forms. The data consisted of product, contact surface, and environmental test results for 

samples that were collected and tested for L. monocytogenes. Establishment names and numbers are not 

reported. These data were extracted from the Data Warehouse (M2K database) via Laboratory Sample 

Flow System (LSFS). Supplementary data were obtained using the Performance-based Inspection System 

(PBIS) reader. 

The PFGE pattern data related to isolate subtyping of Lm-positive samples were provided by the 

Outbreaks Section of the Eastern Laboratory Microbiology Branch (OSEL) of FSIS. Actual PFGE pattern 

designations and pattern matching were done by the Centers for Disease Control and Prevention (CDC). 

In some cases, information contained in FSAs conducted for the RLm program was also used in the 

analysis. 

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Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

3. DATA ANALYSIS PROCEDURES 

FSIS calculated the numbers of positive samples and percentage of positive samples for product, contact 

surface, and environmental samples for April through December 2006 and calendar year 2007. The 

analyses, which included 3,275 samples from 63 establishments in 2006 and 6,210 samples from 127 

establishments in calendar year 2007, focused on 

• the incidence and categorization of positive Lm samples from sampled establishments; 

• types, sources, and PFGE subtyping of Lm isolates from the positive samples; 

• descriptive summaries with respect to 

– Lm control alternatives employed by the establishment, 

– establishment HACCP size, 

– FSIS District, 

– geographic location of the establishment, and 

– season or month of sample collection; and 

• trends in percentage of positive results from 2006 to 2007. 

The Agency also conducted a limited evaluation of FSA reports collected under the RLm program. All 

data analyses were performed through data handling and evaluation techniques using Microsoft Office 

Excel. 

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Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

4. RESULTS AND DISCUSSION 

Data collection under the RLm sampling program began in April 2006. Because FSIS has not prepared an 

RLm data analysis report prior to this one, the Agency evaluated existing data for the periods April 

through December 2006 and calendar year 2007. Sampling data collected under RLm in 2006 and 

calendar year 2007 included product, contact surface, and environmental sampling results. Some analyses, 

notably for types and sources of samples and for L. monocytogenes isolate subtyping, have employed 

combined 2006 and 2007 data. In addition, some limited trend analysis was performed by comparing the 

2006 and 2007 results (see Section 4.13). 

4.1 RLm Testing Results for April through December 2006 

Table 4.1.1 and Figures 4.1.1 through 4.1.3 show the results of testing 3,275 samples from 63 

establishments in the RLm sampling program from April through December 2006. This encompasses 

• 530 RTE food product samples, 

• 1,786 samples from product contact surfaces, and 

• 959 environmental surface samples. 

Overall, 0.6% of the samples were positive for L. monocytogenes. None of the product samples were 

positive for L. monocytogenes, while 4 contact surface (0.2%) and 17 (1.8%) environmental samples 

yielded positive results. 

Table 4.1.1. Detection of L. monocytogenes in Product, Contact Surface, and 

Environmental Samples, April–December 2006 

Positive Samples 

Sample Type 

Total 

Collected No. % 

Product 530 0 0.0 

Contact surface 1,786 4 0.2 

Environmental 959 17 1.8 

Total 3,275 21 0.6 

Of 63 establishments for which samples were collected and tested from April through December 2006, 

about one of every five establishments (22%) had at least one Lm-positive sample (product and/or contact 

and/or environmental). The results of sorting the establishment data by type of sampling program are 

shown in Table 4.1.2 and Figures 4.1.4 and 4.1.5. Most of the positive samples from the 63 

establishments (11, or about 17%) were environmental, while 3 (about 5%) were contact surface. No 

positive product samples were obtained from April through December 2006. 

7 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.1.1. Samples Collected and Tested for L. monocytogenes, April–December 2006 

0

500

1,000

1,500

2,000

Product Contact Surface Environmental

No. of Samples Collected

Figure 4.1.2. Number of Lm-Positive Samples, April–December 2006

0

3

6

9

12

15

18

Product Contact Surface Environmental

No. of Positive Samples

8 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.1.3. Percentage of Lm-Positive Samples, April–December 2006

0.0

0.4

0.8

1.2

1.6

2.0

Product Contact Surface Environmental

% Positive Samples

Table 4.1.2. Number and Percentage of Establishments with at Least One Lm-Positive 

Sample, April–December 2006 

Establishments 

Sample Type No. % 

Product 0 0.0 

Contact surface 3 4.8 

Environmental 11 17.5 

Combined (63 establishments sampled) 14 22.2 

9 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.1.4. Number of Establishments with Lm-Positive Samples, 

April–December 2006 

0

2

4

6

8

10

12

Product Contact Surface Environmental 

No. of Establishments

Figure 4.1.5. Percentage of Establishments with Lm-Positive Samples, 

April–December 2006 

0.0

4.0

8.0

12.0

16.0

20.0

Product Contact 

Surface

Environmental 

% of Establishments 

10 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

4.2 RLm Testing Results for Calendar Year 2007 

Table 4.2.1 and Figures 4.2.1 through 4.2.3 show the results of testing 6,210 samples from 127 

establishments in the RLm sampling program for calendar year 2007. This encompasses 

• 1,012 RTE food product samples, 

• 3,403 contact surface samples, and 

• 1,795 environmental surface samples. 

Overall, 0.7% of the samples were positive for L. monocytogenes. Two (0.2%) of the product samples 

were positive for L. monocytogenes, while positive results were obtained for 12 contact (0.4%) and 32 

(1.8%) environmental samples. 

Table 4.2.1. Detection of L. monocytogenes in Product, Contact Surface, and 

Environmental Samples, Calendar Year 2007 

Positive Samples 

Sample Type 

Total 

Collected No. % 

Product 1,012 2 0.2 

Contact surface 3,403 12 0.4 

Environmental 1,795 32 1.8 

Total 6,210 46 0.7 

Figure 4.2.1. Samples Collected and Tested for L. monocytogenes, 

Calendar Year 2007 

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

Product Contact Surface Environmental

No. of Samples Collected 

11 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.2.2. Number of Lm-Positive Samples, Calendar Year 2007 

0

5

10

15

20

25

30

35

Product Contact Surface Environmental

No. of Positive Samples

Figure 4.2.3. Percentage of Lm-Positive Samples, Calendar Year 2007 

0.0

0.4

0.8

1.2

1.6

2.0

Product Contact Surface Environmental

% Positive Samples

12 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Of the 127 establishments tested in 2007, one of every five establishments (20%) had at least one Lmpositive sample (product and/or contact and/or environmental). These results are similar to those in 2006. 

The results of sorting the establishment data by type of testing program are shown in Table 4.2.2 and 

Figures 4.2.4 and 4.2.5. Most of the establishments with Lm-positive samples had positive results for 

environmental sampling (22, or about 17%). Only 7 (6%) had positive results for contact surface, and 2 

(2%) had positive results for product sampling. 

Table 4.2.2. Number and Percentage of Establishments with at Least One Lm-Positive 

Sample, Calendar Year 2007 

Establishments 

Sample Type No. % 

Product 2 1.6 

Contact surface 7 5.5 

Environmental 22 17.3 

Combined (127 establishments sampled) 25 19.7 

Figure 4.2.4. Number of Establishments with Lm-Positive Samples, Calendar Year 2007 

0

5

10

15

20

25

Product Contact Surface Environmental 

No. of Establishments

13 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.2.5. Percentage of Establishments with Lm-Positive Samples, Calendar Year 2007 

0.0

4.0

8.0

12.0

16.0

20.0

Product Contact 

Surface

Environmental 

% of Establishments 

4.3 Classification of Lm-Positive Samples, April 2006 through December 2007 

Lm-positive samples from the establishments were further characterized based on which establishments 

had samples that were positive in all three sampling programs or in six other possible combinations of 

sampling programs. The results of this categorization for April through December 2006, for calendar year 

2007, and combined for both time periods are shown in Table 4.3.1. For the combined results in 2006 and 

2007, a total of 39 establishments (or about 20% of 190 establishments for which samples were collected 

and tested) had Lm-positive samples as follows: 

• Most of the positive establishments (29 of 39, or 74%) were positive only for environmental 

samples. 

• Another five establishments (12%) were positive only for contact surface samples. 

• Three establishments (8%) were positive for contact surface and environmental samples. 

• Of the two establishments with positive product samples, one also was positive for contact 

surface samples, while the other yielded positive results in all three sampling programs. 

These data suggest that in establishments with Lm-positive product samples, one may also encounter 

positive contact and/or environmental samples. However, most establishments had positive samples in 

only one category (typically contact surface or environmental) collected as part of the RLm sampling 

program. 

14 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Table 4.3.1. Classification of Lm-Positive Samples from Establishments with at Least One 

Positive Sample 

Time Period 

Environmental 

Only 

Contact 

Surface 

Only 

Environmental 

and Contact 

Surface 

Product 

and 

Contact 

Surface

All 

Types 

Total 

Establishments

April–December 

2006 11 3 0 0 0 14 

Calendar year 2007 18 2 3 1 1 25 

Combined 29 5 3 1 1 39 

4.4 Types and Sources of Lm-Positive Samples, April 2006 through December 2007 

From April 2006 through December 2007, a total of 67 Lm-positive samples were obtained under the 

RLm sampling program. Of these, 2 were from product, 16 were from contact surfaces, and 49 were from 

environmental surfaces. Tables 4.4.1 through 4.4.5 show a breakdown of the types and sources of Lmpositive samples by category. These results are as follows: 

• Both product positives were sliced, diced, and shredded meat and poultry (one beef and one 

chicken product [Table 4.4.1]). 

• Of the 16 positive contact surface samples (Table 4.4.2), blades, knives, and scales each had two 

positives, while one positive was found in 10 other contact surface sample types. 

– The rates of Lm-positive samples relative to the numbers of blades, knives, and scales 

sampled ranged from 0.6 to 1.3% (Table 4.4.3). 

• Of the 49 positive environmental surface samples (Table 4.4.4), the highest number of positives 

were found in drains (11, or about 22% of all environmental positives), followed by wheels (9), 

floors (8), and floor mats (3). 

– The rates of Lm-positive samples relative to the approximately 900 drains, wheels, and floors 

sampled ranged from 3.0 to 4.5% (Table 4.4.5). 

– The rate of Lm-positive samples relative to the 12 floor mats sampled was 25%. 

Table 4.4.1. Types of Lm-Positive Product Samples, April 2006–December 2007 

Product Type Positives 

Beef, sliced, diced and shredded, with/without sauce (smoked pastrami) 1 

Chicken, sliced, diced and shredded, with sauce (chicken salad wrap) 1 

Total 2 

15 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Table 4.4.2. Types of Lm-Positive Contact Surface Samples, April 2006–December 2007 

Positive Samples 

Contact Surface Type No. % 

Blade 2 12.5 

Knife 2 12.5 

Scale 2 12.5 

Container 1 6.3 

Conveyer belt 1 8.3 

Glove 1 8.3 

Hopper 1 8.3 

Horn 1 8.3 

Peeler 1 8.3 

Slicer 1 8.3 

Table 1 8.3 

Table/cutting board 1 8.3 

Tray 1 8.3 

Total 16 100.0 

Table 4.4.3. Lm-Positive Rate for the Main Types of Contact Surface Samples, 

April 2006–December 2007 

Positive Samples 

Contact Surface Type 

Total 

Collecteda No. % 

Blade 340 2 0.6 

Knife 155 2 1.3 

Scale 325 2 0.6 

a

Approximate numbers from sample description listings. 

16 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Table 4.4.4. Types of Lm-Positive Environmental Samples, April 2006–December 2007 

Positive Samples 

Environmental Surface Type No. % 

Drain 11 22.4 

Wheel(s) 9 18.4 

Floor 8 16.3 

Floor mat 3 6.1 

Boot 2 4.1 

Equipment framework 2 4.1 

Infrastructure 2 4.1 

Slicer 2 4.1 

Squeegee 2 4.1 

Door 1 2.0 

Drain/floor 1 2.0 

Jack 1 2.0 

Pooled water, vent 1 2.0 

Puller 1 2.0 

Pump 1 2.0 

Rack 1 2.0 

Trash can 1 2.0 

Total 49 100.0 

Table 4.4.5. Lm-Positive Rate for the Types of Environmental Samples, 

April 2006–December 2007 

Positive Samples 

Environmental Surface Type 

Total 

Collecteda No. % 

Drain 360 11 3.1 

Wheel(s) 200 9 4.5 

Floor 265 8 3.0 

Floor mat 12 3 25.0 

a

Approximate numbers from sample description listings (actual number for mat). 

17 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Because of the potential utility of this information for sample collection, the data described in this section 

were presented at advanced EIAO methodology courses over the summer of 2008. This allowed sample 

collectors to begin to use this information immediately to determine locations to collect Lm samples 

within establishments. 

4.5 Isolate Subtyping Results 

PFGE analysis was performed on 69 isolates derived from the 67 positive samples from the RLm 

sampling program. (The additional two isolates were from the same drain sample, for a total of three 

isolates from that one sample.) The results from RLm sampling can be used in conjunction with other 

sampling programs to identify possible cross-contamination and harborage within establishments. As 

shown in Table 4.5.1, a total of 41 different PFGE pattern types were observed among the 69 isolates 

from the RLm program.1

 Thirteen of these patterns were isolated multiple times, with one subtype 

isolated seven times, three subtypes isolated four times, and four subtypes isolated three times (Table 

4.5.1). Interestingly, two different PFGE pattern types were observed among the three isolates from the 

single drain sample. 

Five of the establishments had positive samples obtained in more than one sampling program: 

• three establishments with positive contact surface and environmental, 

• one establishment with positive product and environmental, and 

• one establishment with positive samples in all three programs. 

Based on the PFGE subtyping results for these samples, in only one of these five instances did obvious 

cross-contamination occur. Specifically, samples collected from a product (chicken salad wrap) and an 

associated contact surface (chicken salad container) had matching PFGE patterns. This indicated that the 

specific product contaminant could have spread to or from the contact surface. There were no instances in 

which PFGE patterns of environmental samples matched that of product or contact samples. These results 

indicate that transfer of L. monocytogenes subtypes with matching PFGE patterns between the 

environment and contact surfaces and/or products was not a common occurrence with respect to the RLm 

samples collected. However, such matches have been observed in IVT data for establishments with 

positive RLm results. 

In 11 instances, the same PFGE pattern was observed from multiple product, contact surface, or 

environmental samples within the same establishment, indicating possible cross-contamination of 

different contact surfaces or environmental locations, respectively (Table 4.5.2). This included the 

following: 

• three establishments with two or more matching contact surface isolates; 

• five establishments with two or more matching environmental isolates, including two 

establishments with multiple isolates that matched two different PFGE pattern types; and 

• one establishment with a matching PFGE pattern for isolates from a product and a contact surface 

sample (as noted above). 

These results demonstrate the utility of collecting multiple contact surface or environmental samples for 

the purpose of detecting isolates with a common PFGE pattern from different sources within a single 

 

1 PFGE pattern types are designated by CDC and are part of the PulseNet database, which was accessed on May 7, 2008, for 

purposes of this analysis. Actual pattern types are not shown. 

18 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

establishment. However, at least with respect to the RLm samples collected to date, transfer of specific 

Lm subtypes between the environment and contact surfaces appears to be an uncommon event. 

Evidence of harborage over time could not be determined from the RLm results alone because 

establishments were not sampled multiple times under this program. FSIS systematically reviews PFGE 

data across all Lm sampling programs to determine whether harborage or cross-contamination may have 

occurred within particular establishments and may use the information as a basis to take further actions. 

In the course of doing so, FSIS (specifically, the Microbiology Division of OPHS) keeps a list of the 10 

top PFGE patterns encountered. (This list is updated periodically.) Of the 41 PFGE patterns encountered, 

6 patterns from 18 isolates (representing 26% of all isolates) were on the current top 10 pattern list. The 

number one pattern from the FSIS list was also the number one pattern from the RLm sampling program 

(Table 4.5.1). 

Table 4.5.1. Patterns and Occurrence of Lm PFGE Subtypes Isolated in the RLm 

Program, April 2006–December 2007 

PFGE Pattern Type Occurrence 

% of Total 

Isolates 

Rank in FSIS List of 

Top 10 PFGE Patternsa

1 7 10.1 1 

2 4 5.8 5 

3 4 5.8 — 

4 4 5.8 — 

5 3 4.3 6 

6 3 4.3 — 

7 3 4.3 — 

8 3 4.3 — 

9 2 2.9 — 

10 2 2.9 — 

11 2 2.9 — 

12 2 2.9 4 

13 2 2.9 — 

14 1 1.4 2 

15 1 1.4 7 

All other pattern types 

(single occurrences) 26 37.7 — 

Total 69 100.0 

a The FSIS list of top 10 PFGE patterns encountered is maintained by the Microbiology Division of the Office of Public Health 

Science (OPHS). 

19 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Table 4.5.2. Incidence of Multiple Isolations of the Same PFGE Subtype within the Same 

Establishment, April 2006–December 2007 

Occurrence of Pattern Type 

Establishment 

PFGE Pattern Type 

Within Establishment RLMCONT RLMENV RLMPROD Total

1 1 3 3 

2 1 2 2 

3 1 2 2 

4 1 4 4 

 2 2 2 

5 1 2 2 

 2 2 2 

6 1 2 2 

7 1 2 2 

8 1 2 2 

9 1 1 1 2 

Note: Establishment and Pattern Type are numerical rankings, not identifiers. 

4.6 Results Based on Alternatives Used to Control L. monocytogenes

For the RLm sampling program, establishments use one or more of four possible procedures, or control 

alternatives, for eliminating or inhibiting the growth of L. monocytogenes in the particular RTE products 

produced by each establishment. The four alternative categories are the following: 

• Alternative 1, the lowest-risk category, involves using both a post-lethality treatment (which 

could be a physical treatment or an antimicrobial agent) “that reduces or eliminates 

microorganisms on the product AND an antimicrobial agent or process that suppresses or limits 

the growth of L. monocytogenes” (FSIS Directive 10,240.4, Revision 1, 3/15/2006). 

• Alternatives 2a and 2b, the next higher-risk categories, provide the option of either a postlethality treatment the kills or inhibit microorganisms (2a) or an antimicrobial agent or process 

that specifically inhibits L. monocytogenes (2b). 

• Alternative 3, the highest-risk category, requires the “use of sanitation procedures only” (FSIS 

Directive 10,240.4). 

Accordingly, one would expect the potential of encountering L. monocytogenes in product, contact 

surface, and environmental samples to be greatest in Alternative 3 establishments and least in Alternative 

1 establishments. 

The percentages of product, contact surface, and environmental samples positive for L. monocytogenes

with respect to the four major RTE Lm control Alternative (1, 2a, 2b, and 3) for April through December 

2006 and for calendar year 2007 are shown in Tables 4.6.1 and 4.6.2 and Figures 4.6.1 through 4.6.5. As 

noted previously, no positive product samples were obtained for April through December 2006. Both Lmpositive product samples encountered in 2007 were from Alternative 3 establishments. All Lm-positive 

contact surface samples in both 2006 and 2007 were from establishments that used Alternative 3, 

Alternative 2b, or a combination of Alternatives 2a and 2b. With respect to environmental samples, in 

2006, all Lm-positive samples were from establishments that used Alternatives 2 (2a and/or 2b) and 3. 

20 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

However, in 2007 a relatively large percentage (13%) of Lm-positive environmental samples were from 

establishments that were using both Alternatives 1 and 3. Although the risk associated with employing 

Alternative 1 as a contamination control measure is low, it is uncertain whether these establishments were 

employing Alternative 1 or Alternative 3 at the time of or in the location of sample collection. 

4.7 Results by Establishment HACCP Size 

The percentages of product, contact surface, and environmental samples positive for L. monocytogenes

with respect to each establishment’s HACCP size of large, small, or very small for April through 

December 2006 and calendar year 2007 are shown in Tables 4.7.1 and 4.7.2 and Figures 4.7.1 through 

4.7.5.2

 (As noted previously, no positive product samples were obtained from April through December 

2006.) In 2006, no very small establishments had Lm-positive contact surface or environmental samples. 

However, in 2007, very small establishments had the highest rates of Lm-positive contact surface samples 

and the second highest rates for environmental samples. Conversely, in 2007, large establishments had no 

positive Lm contact surface samples and markedly lower rates of positive Lm environmental samples 

compared to very small and small establishments. The percentage positive rates by establishment HACCP 

size between the time periods may not be comparable because of differences in establishment 

prioritization for RLm sample collection (such as the FSIS risk-based sampling algorithm itself and 

decisions as to which establishments are sampled sooner in the program). 

4.8 Results by Food Product Category 

Results were analyzed as a function of the nine food product categories found on 10,240-1 forms (deli 

products sliced at the producing establishment, deli products to be sliced after distribution, hot dog 

products, fully cooked products, fermented products, dried products, salt-cured products, frozen products, 

and pâté products). The percentages of product, contact surface, and environmental samples positive for 

L. monocytogenes with respect to the nine above-named food product categories for April through 

December 2006 and calendar year 2007 are shown in Figures 4.8.1 and 4.8.2. (As noted previously, no 

positive product samples were obtained from April through December 2006.) In general, the results 

indicated that Lm-positive product samples were often found in establishments that produced deli meat 

products. It is noteworthy that the detection of Lm-positive samples from establishments in nondeli meat 

categories in both 2006 and 2007 was mainly for cooked products. 

4.9 Results by FSIS District 

The percentages of product, contact, and environmental samples positive for L. monocytogenes within 

each FSIS District for April through December 2006 and for calendar year 2007 are shown in Tables 

4.9.1 and 4.9.2 and Figures 4.9.1 through 4.9.5. (As noted previously, no positive product samples were 

obtained from April through December 2006.) Lm-positive rates for contact surface and environmental 

samples collected in each district were somewhat varied. However, it should be noted that in 2007, the 

Atlanta, GA, district had a markedly higher percentage positive rate of L. monocytogenes in contact 

surface samples relative to other districts (greater than 4% in Atlanta compared to less than 2% in other 

districts). Also, with respect to environmental samples, the highest Lm-positive rates for both 2006 and 

2007 were in the Alameda, CA, and Philadelphia, PA, districts. 

 

2

 Large plants have 500 or more employees, small plants have 10 or more employees but fewer than 500, and very small plants 

have fewer than 10 employees or less than $2.5 million in annual sales. 

21 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

4.10 Results by Geographic Region 

To explore possible geographic influences on the detection of L. monocytogenes, FSIS subjectively 

classified the FSIS Districts into the following geographic regions: 

• Northeast (NE)/Mid-Atlantic: Albany, NY; Beltsville, MD; and Philadelphia, PA 

• South: Atlanta, GA; Dallas, TX; Jackson, MS; Raleigh, NC; and Springdale, AR 

• Midwest: Chicago, IL; Des Moines, IA; Lawrence, KS; Madison, WI; and Minneapolis, MN 

• Mountain/Pacific: Alameda, CA, and Denver, CO 

The percentages of product, contact surface, and environmental samples positive for L. monocytogenes

within these four broad geographic regions for April through December 2006 and for calendar year 2007 

are shown in Tables 4.10.1 and 4.10.2 and Figures 4.10.1 through 4.10.5. (As noted previously, no 

positive product samples were obtained from April through December 2006.) In 2007, the two Lmpositive product samples were from separate establishments located in the NE/Mid-Atlantic region of the 

country. With respect to contact surface samples, no Lm-positives samples were collected from 

establishments in the Mountain/Pacific region in 2006 and 2007. Finally, the Lm-positive rate for 

environmental samples from establishments in the Midwest appeared to be lower than the rate in other 

geographic regions both years. 

4.11 Results by Season and Month 

To explore possible seasonal influences on the detection of L. monocytogenes, positive product, contact 

surface, and environmental results were categorized based either on season or month of the year. The 

percentages of product, contact surface, and environmental samples positive for L. monocytogenes by 

season and by month for April through December 2006 and for calendar year 2007 are shown in Figures 

4.11.1 through 4.11.4. The results indicate that Lm-positive environmental samples were isolated across 

all seasons or months, whereas almost all Lm-positive contact surface samples were obtained in the 

summer and fall, or over the last 6 months of the year. This appears appeared to be true in both 2006 and 

2007. The two positive product samples were both obtained in the summer (one in July, the other in 

September). 

22 
Table 4.6.1. Detection of L. monocytogenes by Control Alternative, April–December 20

Positive 

Samples 

Positive 

Samples 

Positive 

Samples 

Alternative 

No. of 

Establishments 

Product 

Samples No. % 

Contact 

Surface 

Samples No. % 

Environmental

Samples No. % 

S

2A/2B 3 39 0 0.0 130 0 0.0 70 0 0.0 2B 14 140 0 0.0 472 2 0.4 244 2 0.8 3 25 153 0 0.0 529 2 0.4 288 10 3.5 Mixed 1/2 3 36 0 0.0 119 0 0.0 60 0 0.0 Mixed 1/3 1 3 0 0.0 8 0 0.0 5 0 0.0 Mixed 1/2/3 3 20 0 0.0 39 0 0.0 22 0 0.0 Mixed 2/3 14 139 0 0.0 489 0 0.0 270 5 1.9 Total 63 530 0 0.0 1,786 4 0.2 959 17 1.8 

23Table 4.6.2. Detection of L. monocytogenes by Control Alternative, Calendar Year 200

Positive 

Samples 

Positive 

Samples 

Positive 

Samples 

Alternative 

No. of 

Establishments 

Product 

Samples No. % 

Contact 

Surface 

Samples No. % 

Environmental

Samples No. % 

S

2A/2B 7 48 0 0.0 151 1 0.7 105 6 5.7 2B 31 315 0 0.0 1,041 0 0.0 565 6 1.1 3 53 287 2 0.7 976 11 1.1 510 13 2.5 Mixed 1/2 5 41 0 0.0 149 0 0.0 75 1 1.3 Mixed 1/3 6 78 0 0.0 262 0 0.0 130 0 13.3 Mixed 1/2/3 2 9 0 0.0 30 0 0.0 15 2 0.0 Mixed 2/3 23 234 0 0.0 794 0 0.0 395 4 1.0 Total 127 1,012 2 0.2 3,403 12 0.4 1,795 32 1.8 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.6.1. Percentage of Lm-Positive Contact Surface Samples by Control Alternative, 

April–December 2006 

0.0

0.1

0.2

0.3

0.4

0.5

2A/2B 2B 3 Mixed 

1/2

Mixed 

1/3

Mixed 

1/2/3

Mixed 

2/3

% Positive Samples

Control Alternative

Figure 4.6.2. Percentage of Lm-Positive Environmental Samples by Control Alternative, 

April–December 2006 

0.0

1.0

2.0

3.0

4.0

2A/2B 2B 3 Mixed 

1/2

Mixed 

1/3

Mixed 

1/2/3

Mixed 

2/3

% Positive Samples

Control Alternative

24 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.6.3. Percentage of Lm-Positive Product Samples by Control Alternative, 

Calendar Year 2007 

0.0

0.2

0.4

0.6

0.8

2A/2B 2B 3 Mixed 

1/2

Mixed 

1/3

Mixed 

1/2/3

Mixed 

2/3

% Positive Samples

Control Alternative

Figure 4.6.4. Percentage of Lm-Positive Contact Samples by Control Alternative, 

Calendar Year 2007 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

2A/2B 2B 3 Mixed 

1/2

Mixed 

1/3

Mixed 

1/2/3

Mixed 

2/3

% Positive Samples

Control Alternative

25 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.6.5. Percentage of Lm-Positive Environmental Samples by Control Alternative, 

Calendar Year 2007 

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

2A/2B 2B 3 Mixed 

1/2

Mixed 

1/3

Mixed 

1/2/3

Mixed 

2/3

% Positive Samples

Control Alternative

26 
27

Table 4.7.1. Detection of L. monocytogenes by Establishment Size, April–December 20

Positive 

Samples 

Positive 

Samples 

Positive 

Samples 

Establishment 

HACCP Size 

Product 

Samples No. % 

Contact 

Surface 

Samples No. % 

Environmental 

Samples No. % 

To

Sam

Large 224 0 0.0 720 2 0.3 376 3 0.8 1,Small 297 0 0.0 1,034 2 0.2 568 14 2.5 1,Very small 9 0 0.0 32 0 0.0 15 0 0.0 Total 530 0 0.0 1,786 4 0.2 959 17 1.8 3,

Table 4.7.2. Detection of L. monocytogenes by Establishment Size, Calendar Year 200

Positive 

Samples 

Positive 

Samples 

Positive 

Samples 

Establishment 

HACCP Size 

Product 

Samples No. % 

Contact 

Surface 

Samples No. % 

Environmental 

Samples No. % 

To

Sam

Large 337 0 0.0 1,139 0 0.0 585 2 0.3 2,Small 637 2 0.3 2,139 8 0.4 1,143 29 2.5 3,Very small 38 0 0.0 125 4 3.2 67 1 1.5 Total 1,012 2 0.2 3,403 12 0.4 1,795 32 1.8 6,
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.7.1. Percentage of Lm-Positive Contact Samples by Establishment Size, 

April–December 2006 

0.0

0.1

0.1

0.2

0.2

0.3

0.3

Large Small Very Small

% Positive Samples

HACCP Size

Figure 4.7.2. Percentage of Lm-Positive Environmental Samples by Establishment Size, 

April–December 2006 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Large Small Very Small

% Positive Samples

HACCP Size

28 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.7.3. Percentage of Lm-Positive Product Samples by Establishment Size, 

Calendar Year 2007 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Large Small Very Small

% Positive Samples

HACCP Size

Figure 4.7.4. Percentage of Lm-Positive Contact Samples by Establishment Size, 

Calendar Year 2007 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Large Small Very Small

% Positive Samples

HACCP Size

29 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.7.5. Percentage of Lm-Positive Environmental Samples by Establishment Size, 

Calendar Year 2007 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Large Small Very Small

% Positive Samples

HACCP Size

Figure 4.8.1. Percentage of Lm-Positive Samples by Food Product Category, 

April–December 2006 

0

1

2

3

4

5

6

% Positive Samples

Contact Surface Samples

Environmental Samples

30 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.8.2. Percentage of Lm-Positive Samples by Food Product Category, 

Calendar Year 2007 

0

1

2

3

4

5

6

% Positive Samples

Product Samples

Contact Surface Samples

Environmental Samples

31 
Table 4.9.1. Detection of L. monocytogenes by FSIS District, April–December 2006 

32

Positive 

Samples 

Positive 

Samples 

Positive 

Samples 

Product 

Samples No. % 

Contact 

Samples No. % 

Environmental 

Samples No. % 

Sa

Chicago, IL 42 0 0 147 1 0.7 75 1 1.3 Des Moines, IA 33 0 0 109 1 0.9 53 1 1.9 Lawrence, KS 39 0 0 130 0 0.0 64 0 0.0 Madison, WI 62 0 0 205 0 0.0 115 0 0.0 Minneapolis, MN 48 0 0 160 0 0.0 80 1 1.3 Atlanta, GA 30 0 0 119 0 0.0 56 2 3.6 Dallas, TX 38 0 0 118 0 0.0 59 0 0.0 Jackson, MS 26 0 0 75 0 0.0 49 1 2.0 Raleigh, NC 36 0 0 130 2 1.5 65 2 3.1 Springdale, AR 39 0 0 122 0 0.0 72 3 4.2 Albany, NY 39 0 0 133 0 0.0 65 0 0.0 Beltsville, MD 36 0 0 134 0 0.0 70 0 0.0 Philadelphia, PA 14 0 0 42 0 0.0 41 2 4.9 Alameda, CA 25 0 0 77 0 0.0 51 4 7.8 Denver, CO 23 0 0 85 0 0.0 44 0 0.0 Total 530 0 0.0 1,786 4 0.2 959 17 1.8 3
Table 4.9.2. Detection of L. monocytogenes by FSIS District, Calendar Year 2007 

33

Positive 

Samples 

Positive 

Samples 

Positive 

Samples 

Product 

Samples No. % 

Contact 

Samples No. % 

Environmental 

Samples No. % 

Sa

Chicago, IL 84 0 0.0 280 0 0.0 145 1 0.7 Des Moines, IA 101 0 0.0 326 0 0.0 178 1 0.6 Lawrence, KS 54 0 0.0 179 0 0.0 125 1 0.8 Madison, WI 83 0 0.0 309 3 1.0 162 3 1.9 Minneapolis, MN 86 0 0.0 287 0 0.0 150 1 0.7 Atlanta, GA 26 0 0.0 86 4 4.7 48 1 2.1 Dallas, TX 45 0 0.0 152 0 0.0 75 0 0.0 Jackson, MS 45 0 0.0 145 0 0.0 61 0 0.0 Raleigh, NC 69 0 0.0 240 0 0.0 119 4 3.4 Springdale, AR 69 0 0.0 220 0 0.0 112 1 0.9 Albany, NY 89 1 1.1 292 2 0.7 149 5 3.4 Beltsville, MD 47 1 2.1 177 2 1.1 90 0 0.0 Philadelphia, PA 98 0 0.0 318 1 0.3 182 8 4.4 Alameda, CA 69 0 0.0 233 0 0.0 115 6 5.2 Denver, CO 47 0 0.0 159 0 0.0 84 0 0.0 Total 1,012 2 0.2 3,403 12 0.4 1,795 32 1.8 6
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.9.1. Percentage of Lm-Positive Contact Surface Samples by FSIS District, 

April–December 2006 

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

Chicago, IL Des Moines, IA Raleigh, NC

% Positive Samples

Figure 4.9.2. Percentage of Lm-Positive Environmental Samples by FSIS District, 

April–December 2006 

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

% Positive Samples 

34 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.9.3. Percentage of Lm-Positive Product Samples by FSIS District, 

Calendar Year 2007 

0.0

1.0

2.0

3.0

4.0

5.0

6.0

Albany, NY Beltsville, MD

% Positive Samples

Figure 4.9.4. Percentage of Lm-Positive Contact Samples by FSIS District, 

Calendar Year 2007 

0.0

1.0

2.0

3.0

4.0

5.0

6.0

% Positive Samples

35 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.9.5. Percentage of Lm-Positive Environmental Samples by FSIS District, 

Calendar Year 2007 

0.0

1.0

2.0

3.0

4.0

5.0

6.0

% Positive Samples

36 
Table 4.10.1. Detection of L. monocytogenes by Geographic Region, April–December 20

Positive 

Samples 

Positive 

Samples 

Positive 

Samples 

Region 

Product 

Samples No. % 

Contact 

Samples No. % 

Environmental 

Samples No. % 

To

Sam

Midwest 224 0 0.0 751 2 0.3 387 3 0.8 1,3South 169 0 0.0 564 2 0.4 301 8 2.7 1,0NE/Mid-Atlantic 89 0 0.0 309 0 0.0 176 2 1.1 5Mountain/Pacific 48 0 0.0 162 0 0.0 95 4 4.2 3Total 530 0 0.0 1,786 4 0.2 959 17 1.8 3,2

Table 4.10.2. Detection of L. monocytogenes by Geographic Region, Calendar Year 200

37Positive 

Samples 

Positive 

Samples 

Positive 

Samples 

Region 

Product 

Samples No. % 

Contact 

Samples No. % 

Environmental 

Samples No. % 

To

Sam

Midwest 408 0 0.0 1,381 3 0.2 760 7 0.9 2,5South 254 0 0.0 843 4 0.5 415 6 1.4 1,5NE/Mid-Atlantic 234 2 0.9 787 5 0.6 421 13 3.1 1,4Mountain/Pacific 116 0 0.0 392 0 0.0 199 6 3.0 7Total 1,012 2 0.2 3,403 12 0.4 1,795 32 1.8 6,2
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.10.1. Percentage of Lm-Positive Contact Surface Samples by Geographic Region, 

April–December 2006 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Midwest South Northeast/

Mid-Atlantic 

Mountain/Pacific 

% Positive Samples

Figure 4.10.2. Percentage of Lm-Positive Environmental Samples by Geographic Region, 

April–December 2006 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Midwest South Northeast/

Mid-Atlantic 

Mountain/Pacific 

% Positive Samples

38 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.10.3. Percentage of Lm-Positive Product Samples by Geographic Region, 

Calendar Year 2007 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Midwest South Northeast/

Mid-Atlantic 

Mountain/Pacific 

% Positive Samples

Figure 4.10.4. Percentage of Lm-Positive Contact Surface Samples by Geographic Region, 

Calendar Year 2007 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Midwest South Northeast/

Mid-Atlantic 

Mountain/Pacific 

% Positive Samples

39 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.10.5. Percentage of Lm-Positive Environmental Samples by Geographic Region, 

Calendar Year 2007 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Midwest South Northeast/

Mid-Atlantic 

Mountain/Pacific 

% Positive Samples

Figure 4.11.1. Percentage of Lm-Positive Samples by Season, April–December 2006 

0

0.5

1

1.5

2

2.5

Spring Summer Fall

% Positive Samples

Product

Contact Surface

Environmental

40 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.11.2. Percentage of Lm-Positive Samples by Season, Calendar Year 2007 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Winter Spring Summer Fall

% Positive Samples

Product

Contact Surface

Environmental

4.12 Food Safety Assessment (FSA) Results 

For 2006 and calendar year 2007, FSIS determined that it was impractical to review all FSAs completed 

by the Office of Field Operations (OFO) for the RLm program. However, the Agency reviewed the results 

of a selected number of FSAs associated with positive RLm results. In the future, when FSAs are 

automated to facilitate data analysis, the Agency will conduct a correlation analysis of FSAs and RLm 

test results. 

FSA reports were reviewed for 19 establishments with a total of 31 positive samples (2 RLMPROD, 11 

RLMCONT, and 18 RLMENVR) collected from RLms performed in calendar year 2007. For these 19 

FSAs, HACCP-related issues were identified in 11, sanitation-related issues were identified in 9, and 

violations of regulation 9 CFR 430.4 were found in 10. Some issues identified during the FSAs included 

the following: 

• The establishment failed to document corrective actions taken in response to establishment 

positives. 

• Management at the establishment was not implementing, verifying, and monitoring the HACCP 

plan. 

• The establishment failed to conduct the Listeria swab sampling of contact surfaces at the 

frequency stated in their Listeria prerequisite program. 

• Establishment employees were not following good manufacturing practices (GMPs) to avoid 

cross-contamination in the establishments. 

41 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.11.3. Percentage of Lm-Positive Samples by Month, April–December 2006 

0

1

2

3

4

5

6

7

8

% Positive Samples

Product

Contact Surface

Environmental

Figure 4.11.4. Percentage of Lm-Positive Samples by Month, Calendar Year 2007 

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

% Positive Samples

Product

Contact Surface

Environmental

42 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

The issues identified during the FSAs can be addressed through a) a Noncompliance Record 

(NR) which is an official record of noncompliance with one or more regulatory requirements, b) 

a 30 Day Reassessment Letter (issued when more information is needed to determine regulatory 

compliance but it is not an enforcement letter), c) a Notice of Intended Enforcement (NOIE), or d) a 

notice of suspension in which inspection activities are suspended until the plant comes into 

compliance. Of the actions taken by the districts in response to the FSA findings, 10 resulted in NRs, 

2 resulted in 30 Day Reassessment Letters and NRs, 5 resulted in NOIEs, 1 resulted in a letter of 

warning, and 1 resulted in a notice of suspension. 

4.13 Trend Analysis of Combined RLm Data: April 2006 through December 2007 

Because the 2006 data begin in April, numbers of samples and Lm-positive results for 2006 and 2007 

cannot be compared directly on a year-to-year basis. However, the data for 2006 and 2007 can be 

compared based on percentages of Lm-positive samples in each category analyzed. Accordingly, Figures 

4.13.1 through 4.13.4 show comparative results for the rates of Lm-positive total, product, contact surface, 

and environmental samples for each year. Based on these results, the Lm-positive rates 

• increased for product samples (0.2% in 2007 versus 0.0% in 2006), 

• increased for contact surface samples (0.4% in 2007 versus 0.2% in 2006), and 

• were virtually unchanged for environmental samples (1.8% in both years). 

Given the relatively recent implementation of the RLm sampling program, these increases may represent 

normal variations in the presence and detection of L. monocytogenes in the establishments from which 

samples were collected. 

Trends in the percentages of establishments with at least one positive sample in any of the three sampling 

programs for 2006 and 2007 are shown in Figure 4.13.5. In both years, about one of every five 

establishments had at least one positive sample. Figures 4.13.6 through 4.13.8 show comparative results 

for the rates of establishments with at least one positive sample. Based on these results, the number of 

establishments with at least one positive sample 

• increased for product samples (1.6% in 2007 versus 0.0% in 2006), 

• was similar for contact surface samples (about 5% in both years), and 

• was similar for environmental samples (about 17% in both years). 

43 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.13.1. Percentage of Total Samples Positive for L. monocytogenes, 

April 2006–December 2007 

0.0

0.2

0.4

0.6

0.8

April–December

2006

January–December

2007

% Positive Samples

Figure 4.13.2. Percentage of Product Samples Positive for L. monocytogenes, 

April 2006–December 2007 

0.0

0.1

0.2

0.3

0.4

April–December 2006 January–December 

2007

% Positive Samples

44 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.13.3. Percentage of Contact Surface Samples Positive for L. monocytogenes, 

April 2006–December 2007 

0.0

0.1

0.2

0.3

0.4

April–December 

2006

January–December

2007

% Positive Samples

Figure 4.13.4. Percentage of Environmental Samples Positive for L. monocytogenes, 

April 2006–December 2007 

0.0

0.4

0.8

1.2

1.6

2.0

April–December

2006

January–December

2007

% Positive Samples

45 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.13.5. Percentage of Establishments with at Least One Lm-Positive Sample (All 

Types), April 2006–December 2007 

0

5

10

15

20

25

April–December 

2006

January–December 

2007

% of Establishments

Figure 4.13.6. Percentage of Establishments with Lm-Positive Product Samples, 

April 2006–December 2007 

0

0.4

0.8

1.2

1.6

2

April–December

2006

January–December

2007

% of Establishments

46 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Figure 4.13.7. Percentage of Establishments with Lm-Positive Contact Surface Samples, 

April 2006–December 2007 

0

1

2

3

4

5

6

April–December

2006

January–December

2007

% of Establishments

Figure 4.13.8. Percentage of Establishments with Lm-Positive Environmental Samples, 

April 2006–December 2007 

0

5

10

15

20

April–December

2006

January–December

2007

% of Establishments

47 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

48 

5. SUMMARY AND CONCLUSIONS 

FSIS analyzed data with respect to the detection of L. monocytogenes in product, contact surface, and 

environmental samples collected under the RLm sampling program for April through December 2006 

(program inception) and for calendar year 2007. Overall, 3,275 samples from 63 establishments were 

tested in 2006, and 6,210 samples from 127 establishments were tested in 2007. The incidence of Lmpositive samples was low relative to the total numbers of samples collected in each year. Lm-positive 

product samples ranged from 0 to 0.2%, Lm-positive contact surface samples ranged from 0.2 to 0.4%, 

and Lm-positive environmental samples ranged from 1.6 to 1.7%. In comparison, Lm-positive product 

samples from the ALLRTE sampling program were 0.6% and 0.4% in 2006 and 2007, respectively, and 

Lm-positive product samples from the RTE001 sampling program were 0.5% in both 2006 and 2007. 

Results based on percentages of establishments with Lm-positive results. Results based on the 

percentages of positive samples obtained from these establishments tell a somewhat different story. About 

one in 5 establishments had environmental samples that were positive for L. monocytogenes, while about 

one in 20 had positive contact surface samples. Thus, the RLm project helps identify establishments that 

have L. monocytogenes somewhere in the environment and, thus, have a potential for product 

contamination. The data indicate that collecting multiple contact surface and environmental samples 

during a single production shift increases the likelihood of finding L monocytogenes in an establishment. 

In that sense, the RLm program serves as a proactive sampling project. That is, it identifies establishments 

in which the risk of product contamination may be higher before contamination is actually identified in 

the products themselves. The use of from 1 to 3 sampling units per establishment (to collect 3 product, 10 

contact, and 5 environmental samples per unit) likely contributed to the detection of positive contact 

surface and environmental samples. 

Results based on type of Lm-positive sample. Of the 16 contact surface samples that were positive for 

L. monocytogenes, blades, knives, and scales were each Lm positive two times, while 10 other types of 

contact samples were Lm positive as single events. Of the 49 Lm-positive environmental samples, drains, 

wheels, and floors/floor mats were at the top of the list, with 13 other types of environmental samples 

yielding only one or two positive samples. Drains are considered to be a likely habitat for L. 

monocytogenes in the environment, and in fact, about 22% of the Lm-positive environmental samples 

were from drains. It should be noted that the detection of L. monocytogenes in the environment is not, in 

and of itself, an indicator that a control problem exists. However, under FSIS Directive 10,240.5, Lmpositive environmental samples may be considered evidence that an establishment’s products are 

produced under unsanitary conditions. 

Results based on PFGE pattern. The designers of the RLm sampling program believed that collecting 

and testing multiple product, contact surface, and environmental samples from a given establishment 

might demonstrate how strains of L. monocytogenes could move from the environment to product contact 

surfaces and eventually contaminate a given product. Determining the PFGE pattern for each positive 

isolate aids in analyzing the likelihood that this occurs. Finding the same electrophoretic patterns in 

isolates from different locations would provide evidence of how specific strains are spread. An analysis of 

the PFGE subtyping data for 2006 and 2007 showed little relationship between isolates from Lm-positive 

food product, contact surface, and/or environmental samples. This was mainly because only 5 of 39 

establishments had positive samples in more than one RLm category (three establishments with samples 

positive in contact surface and environmental, one with samples positive in product and contact surface, 

and one with samples positive in all three sampling programs). The PFGE subtypes of the isolates from 

the establishment with Lm-positive product (smoked pastrami), contact surface, and environmental 

samples were different from one another. However, the PFGE subtype of the isolate from an 

establishment with Lm-positive product and contact surface matched (chicken salad wrap and an 

associated chicken salad container). In short, transfer of L. monocytogenes between the environment and 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

49 

contact surfaces and/or products was not a common occurrence, based on the results for the RLm samples 

collected for testing. However, because few establishments had combined Lm-positive product, contact 

surface, and environment samples in 2006 and 2007, an objective evaluation of data for recovered isolates 

may be better achieved over time and in conjunction with an analysis of IVT “for cause” data. IVT results 

from establishments with positive RLm samples have, in fact, yielded instances of matching PFGE 

patterns for isolates from multiple sources (product, contact surface, and/or environmental) within a given 

establishment. Still, positive results in any one sampling category may indicate a potential for broader 

contamination problems within a given establishment. 

Results based on Lm control alternative. Results based on Lm control alternatives employed by the 

establishments showed that positive samples were obtained from Lm control Alternative 2b and 3 in the 

majority of instances. These data appear to reinforce the concept that Alternative 3 (sanitation 

only/highest risk) and Alternative 2b (antimicrobial treatment/higher-risk) establishments are more at risk 

than Alternative 1 (and possibly even category 2a) establishments with respect to detecting samples 

positive for L. monocytogenes. This observation may be more applicable to positive product and contact 

samples than to positive environmental samples, which were found in establishments that were classified 

as using mixed Alternatives 1 and 2 and, in particular, mixed Alternatives 1 and 3, in 2007 (but not 2006). 

Additionally, demonstrating the migration of specific Lm isolates from environment to contact surface to 

product would represent a means of documenting the failure of Lm control measures, particularly control 

Alternative 3 (sanitation control only). In that regard, the fact that RLm sampling only found a single 

instance of product/contact surface positives may be evidence that Alternative 3 (sanitation only) 

programs can work as an Lm control measure. Going forward, the analysis of data related to Lm control 

alternatives will benefit from planned or newly implemented improvements in information entered on 

10,240 forms. 

Results based on size, product category, district, geographic region, month, and season. Results 

based on establishment HACCP sizes were not meaningful for comparisons on a year-to-year basis 

because positive contact samples came only from large and small establishments in 2006 and from very 

small and small establishments in 2007. This shift in positive results by establishment size likely resulted 

from the sampling algorithm and decisions related to which establishments should be sampled over time. 

Results based on food product categories showed that most of the Lm-positive samples were from 

establishments that produced deli meats and hot dogs. Comparisons of results by FSIS District and 

geographic region will be useful on an ongoing basis but were not meaningful for this analysis because of 

the short time period of the data. Finally, analysis of results by month and season indicated that Lmpositive environmental samples were obtained at all times of the year, whereas positive contact surface 

samples were obtained mainly in the latter half of the year (summer and fall). 

Results based on year-to-year trends. Trends in the percentages of Lm-positive results from 2006 to 

2007 were examined. Percentages of Lm-positive product and contact surface samples increased slightly 

but were essentially unchanged for environmental samples. The percentages of establishments with Lmpositive contact surface and environmental samples were similar, at about 5% and about 17%, 

respectively, for both 2006 and 2007. These results should be interpreted with caution because 2 years’ 

worth of data is not sufficient for an objective evaluation of the effectiveness of the RLm sampling 

program. It cannot be discerned from these data whether changes from 2006 to 2007 reflect true trends or 

normal variations in sampling results. Furthermore, the data represent results from less than 200 of over 

2,000 establishments that are subject to regulation 9 CFR 430. Because of the nature of the sampling 

algorithm, along with decisions on which establishments are sampled when, these year-to-year results are 

not fully representative of all establishments sampled in the RLm program. Evidence of this includes the 

results by establishment HACCP size, in which marked shifts occurred in 2006 versus 2007 with respect 

to the size of establishments with the most Lm-positive samples. FSIS expects that the 2008 data, once 

obtained and analyzed, will provide for an expanded evaluation of the data trends. This should provide an 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

improved perspective for meaningful evaluation of RLm program effectiveness with respect to the 

detection of L. monocytogenes in food products and food processing environments. 

Next steps. The following is a list of actions that are being implemented subsequent to the completion of 

this report and its presentation to/acceptance by the appropriate FSIS Offices and Management Council: 

• Presentation of these results at the International Association for Food Protection annual meeting 

in August 2009. 

• Publication of this data analysis in a peer-reviewed scientific journal. 

• An examination of the data from this report with respect to applying them to preventing 

foodborne outbreaks of L. monocytogenes. This would include possible modifications of existing 

compliance guidelines and other regulatory practices that help protect public health. 

• Reinitiation of hands-on training for RLm/IVT sample collection. 

• Analysis of RLm results for calendar year 2008. 

50 
Results of Data Analysis for the Listeria monocytogenes Risk-based Sampling Program, April 2006 through December 2007 

Appendix A: FSIS Scheduling Criteria for Routine Lm Risk-based (RLm) 

Sampling Program 

Before the month when samples are to be collected, FSIS uses a statistical algorithm to generate a risk 

ranking of establishments producing post-lethality exposed RTE meat and poultry products. The 

following criteria are then used to identify establishments from the risk ranking to be tested for Listeria 

monocytogenes in food product, contact surface, and environmental samples under the Routine Lm Riskbased (RLm) Sampling Program: 

1. Once RLm sampling has been conducted in an establishment, that establishment will not be 

eligible for scheduling again for a 24-month period. 

2. If there is a current-month positive result from any FSIS Lm sampling project, the Agency 

conducts FSAs and IVT at the establishment: 

a. If positive results are found during the IVT, the RLm will not be scheduled until 6 months 

after the IVT and FSA and any accompanying regulatory actions are complete. 

b. If the IVT test results were negative, RLm sampling would revert back to the 24-month 

sampling cycle. 

3. RLm sampling at an establishment will also not be scheduled for 6 months after closeout of an 

Lm-related NOIE, suspension, or other enforcement action. 

4. Previously, FSIS did not schedule RLm testing in more than one establishment operated by the 

same corporation in the same month. This restriction will not apply in FY08. 

5. Collecting RLm samples will no longer take precedence over the other RTE sampling programs 

(i.e., ALLRTE and RTE001). If FSIS Lm sampling projects are scheduled at the same 

establishment over the same time period, all samples will be collected as scheduled. 

51