Impact of the COVID-19 Pandemic on the National Health and Nutrition Examination Surveys

Ryne Paulose-Ram, Ph.D.

Acting Director, Division of Health and Nutrition Examination Surveys

FCSM 2021 Research and Policy Conference 

November 2, 2021

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In March 2020, NHANES was in the second year of its 2019 – 2020 survey cycle.

All 2020 data collection was suspended on March 16, 2020 due to COVID-19.

NHANES mobile exam center (MEC) trailers were parked in Maryland.

NHANES 2019 – 2020 Data Collection

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Deployment of NHANES staff

Contact tracing, Quarantine station, FEMA National Response Coordination Center (NRCC) 

Trailers / trucks for COVID-19 testing

CLIA certified labs

Offered use to DOH in NY, MD, and DC

4/24/2020 we transferred our truck to DC’s Dept of Forensic Sciences, DOH for mobile testing 

     of DC residents

Explored serology testing for SARS-CoV-2

Burden estimates for severe obesity and other health conditions

NHANES assistance with COVID-19 Response

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Data from an incomplete NHANES 2019-2020 cycle

As of mid-March 2020, 18 of 30 planned locations for the full 2-year cycle were visited

No feasible way to safely resume in-person exams in 2020

2019 – March 2020 sample not nationally representative

No method to create sample weights

Data release could increase disclosure risk

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A solution: a 2017-March 2020 pre-pandemic data file

Evaluated incomplete 2019-2020 sample

Examined non-response bias

Discussed with NCHS Board of Scientific Counselors

Decided on a statistical approach to combine... 

a probability sample (2017-2018)

with a partial probability sample (2019-March 2020)

Resulting pre-pandemic data file can be used to make national estimates

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2017-March 2020 Pre-Pandemic Data

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NHANES 2021– 2022 

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NHANES 2021 – 2022 Data Collection
|                 | Screening Households | Sample Participant Interviews | Examinations at MEC | MEC Closing Date |
|-----------------|----------------------|-------------------------------|---------------------|------------------|
| Dress Rehearsal | June 14              | July 26                       | Aug 15              | Sept 25          |

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NHANES 2021 – 2022 Data Collection
|                 | Screening Households | Sample Participant Interviews | Examinations at MEC | Closing Date |
|-----------------|----------------------|-------------------------------|---------------------|--------------|
| Dress Rehearsal | June 14              | July 26                       | Aug 15              | Sept 25      |
| Stand 428       | July 12              | Aug 23                        | Sept12              | Oct 18       |

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NHANES 2021 – 2022 Data Collection
|                 | Screening Households | Sample Participant Interviews | Examinations at MEC | Closing Date |
|-----------------|----------------------|-------------------------------|---------------------|--------------|
| Dress Rehearsal | June 14              | July 26                       | Aug 15              | Sept 25      |
| Stand 428       | July 12              | Aug 23                        | Sept12              | Oct 18       |
| Stand 429       | July 29              | Sept 9                        | Sept 29             | Nov 6        |
| Stand 430       | Aug 6                | Sept 18                       | Oct 23              | Dec 2        |
| Stand 431       | Sept 7               | Oct 18                        | Nov 8               | Dec 18       |
| Stand 432       | Oct 4                | Nov 15                        | Dec 6               | Jan 23       |

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When we returned to the field, we did not expect infection rates to be zero

As a result, several changes were made

Guiding principles around these changes were to:

Promote the safety of survey participants and field staff  

Shorten the face-to-face contact in the home and the MEC 

Preserve the essential data collection needed to monitor the nation’s health 

Reduce respondent burden in order to maximize response rates  

NHANES 2021 – 2022 

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2021 – 2022 Sample Design

No oversampling by race and ethnic groups

No oversampling low-income white/other group

In every selected dwelling unit...

All persons 0-19 years of age are eligible to participate

All 60+ years are eligible

1-2 persons 20-59 years, depending on number of persons in HH 20-59

About half the number of DUs will need to be screened than in 2019

Target examined sample ~10,000 persons across the 30 PSUs; Each 15 nationally representative

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Prior to starting in an NHANES location, COVID risk levels are closely monitored

NHANES uses the 7-day rolling average for new cases per 100K to classify counties into...

green (less than one case), 

yellow (between 1 and 9 cases), 

orange (between 10 and 24 cases), and 

red (more than 24 cases) risk levels. 

In-person data collection only occurs after assessing a county’s risk level and vaccination rates, field staff vaccination rates, and the latest CDC guidance. 

Monitoring COVID-19 in the field

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Prior to starting in an NHANES location, COVID risk levels are closely monitored

NHANES uses the 7-day rolling average for new cases per 100K to classify counties into...

green (less than one case), 

yellow (between 1 and 9 cases), 

orange (between 10 and 24 cases), and 

red (more than 24 cases) risk levels. 

In-person data collection only occurs after assessing a county’s risk level and vaccination rates, field staff vaccination rates, and the latest CDC guidance. 

Monitoring COVID-19 in the field
| Stand | Interview Start   |
|-------|-------------------|
| 695   | Mon, Jul 26, 2021 |
| 428   | Mon, Aug 23, 2021 |
| 429   | Thu, Sep 9, 2021  |
| 430   | Sat, Sep 18, 2021 |
| 431   | Mon, Oct 18, 2021 |
| 432   | Mon, Nov 15, 2021 |

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A multi-mode approach allows screener responses via web, paper, phone or in-person interview.  

Mailings include:

Introductory Letter – push to the web (and phone option)

Reminder Postcard, 7 days later – push to the web (and phone option)

Follow-up Letter via FedEx, 10 days later - push to the web, also includes a paper screener

Final Letter, 10 days later - push to the web, with statement noting an upcoming field interviewer visit

2021 – 2022 Household Screening

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A multi-mode approach allows screener responses via web, paper, phone or in-person interview.  

Mailings include:

Introductory Letter – push to the web (and phone option)

Reminder Postcard, 7 days later – push to the web (and phone option)

Follow-up Letter via FedEx, 10 days later - push to the web, also includes a paper screener

Final Letter, 10 days later - push to the web, with statement noting an upcoming field interviewer visit

2021 – 2022 Household Screening
| Contact mode among completed Household Screeners |                       |           |           |
|--------------------------------------------------|-----------------------|-----------|-----------|
|                                                  | Dress Rehearsal Stand | Stand 428 | Stand 429 |
| Web, Paper, or Phone                             | 20%                   | 22%       | 19%       |
| In-person                                        | 80%                   | 78%       | 81%       |

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Sample Participant (SP) and family questionnaire are now administered by telephone, with an option for in-person

SP questionnaire reduced by over 50%; Family questionnaire reduced by about a quarter

In-home collection of infant formula, salt use, and home water were all discontinued 

In-home collection of individual prescription medications through medication inventory method was discontinued. 

Dietary supplement collection was moved to after the MEC visit with the dietary interview. 

2021 – 2022 Home Interview

-

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Sample Participant (SP) and family questionnaire are now administered by telephone, with an option for in-person

SP questionnaire reduced by over 50%; Family questionnaire reduced by about a quarter

In-home collection of infant formula, salt use, and home water were all discontinued 

In-home collection of individual prescription medications through medication inventory method was discontinued. 

Dietary supplement collection was moved to after the MEC visit with the dietary interview. 

2021 – 2022 Home Interview
| Interview mode among persons interviewed |                       |           |            |
|------------------------------------------|-----------------------|-----------|------------|
|                                          | Dress Rehearsal Stand | Stand 428 | Stand 429* |
| In-person                                | 64.4%                 | 62.5%     | 10.1%      |
| Phone                                    | 35.6%                 | 37.5%     | 89.9%      |
| * Closes Nov 6                           |                       |           |            |

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| Age Group (years)    | Dress Rehearsal Stand(minutes) | Stand 428(minutes) |
|----------------------|--------------------------------|--------------------|
| SP Questionnaire     |                                |                    |
| 0-15                 | 9.5                            | 9.1                |
| 16-19                | 17.2                           | 13.5               |
| 20-39                | 16.7                           | 16.9               |
| 40-59                | 18.4                           | 18.4               |
| 60+                  | 19.2                           | 20.4               |
| Family Questionnaire |                                |                    |
|                      | 7.6                            | 8.4                |

Median time of home interview among interviewed persons

at

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Median time of home interview among interviewed persons
| Age Group (years)    | Dress Rehearsal Stand(minutes) | Stand 428       |                          |
|----------------------|--------------------------------|-----------------|--------------------------|
| Age Group (years)    | Dress Rehearsal Stand(minutes) | Median(minutes) | 90th Percentile(minutes) |
| SP Questionnaire     |                                |                 |                          |
| 0-15                 | 9.5                            | 9.1             | 19.6                     |
| 16-19                | 17.2                           | 13.5            | 25.7                     |
| 20-39                | 16.7                           | 16.9            | 34.6                     |
| 40-59                | 18.4                           | 18.4            | 34.6                     |
| 60+                  | 19.2                           | 20.4            | 41.6                     |
| Family Questionnaire |                                |                 |                          |
|                      | 7.6                            | 8.4             | 17.0                     |

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All incentives paid using debit cards

Total incentive stays the same with some modifications

SP interview incentive added - $25

MEC Exam

Age 0-11y - $40, 12-15y - $60, and 16 and older - $85 

Transportation and child/adult care unchanged

No fasting incentive

Post-exam interviews

Dietary Day 1 - $25, Dietary Day 2 - $25, and Food Consumer Behavior Survey phone follow-up module - $15

2021 – 2022 Incentive Structure

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Structural Changes to trailers to promote social distancing

Modified MEC flow options to reduce interaction with others

New exam schedule with 4 or 5, 2.5h sessions per day that accommodate about 5 SPs each session. 

Extra cleaning between SPs 

Staff 

Wear PPE (masks, gloves, lab coat) 

Be vaccinated 

Conduct daily symptom screening

Participants and visitors, prior to MEC entry 

CDC COVID-19 screening questions

Temperature checks

Wear face mask

2021 – 2022 Mobile Examination Center (MEC)

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Two antibody tests added:

Spike-based tests will detect antibodies after vaccination and natural infection.

Nucleocapsid-based tests will detect antibodies only after natural infection.

Produce nationally representative prevalence estimates of past infection and/or vaccine-induced immunity among NHANES participants aged 1 year and older using blood-based (serological) antibody testing.

COVID-19 Specific Content: SARS-CoV-2 serology testing

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Prior to the health exam and blood draw at the mobile exam center, participants are asked the following COVID-19 questions during their home interview: 

COVID-19 Specific Content: Home Interview Questions

How many doses of COVID-19 vaccine have you received?  In what month and year did you receive the most recent dose of vaccine for COVID-19?  

Have you ever had an overnight stay in a hospital for suspected or confirmed COVID-19?

Has anyone in your household ever tested positive for coronavirus or COVID-19?

Do you currently have a health condition that a doctor or other health professional told you weakens the immune system, making it easier for you to get sick? 

In the past 12 months, have you taken prescription medication or had any medical treatments that a doctor or other health professional told you/ would weaken your immune system? 

During the past 12 months, have you had a flu vaccination?

Have you ever had COVID-19, or the illness caused by the Coronavirus 2019? 

How would you describe your symptoms when they were at their worst?  (None, Mild, Moderate, Severe)

Have you ever been tested for coronavirus or COVID-19?   

Did the swab or saliva test find that you had coronavirus or COVID-19? What was the date of your positive COVID-19 test. This does not include the blood test.

Have you ever had an antibody blood test to determine if you had coronavirus or COVID-19 in the past?  Did the blood test find that you had antibodies for coronavirus or COVID-19? What was the date of this blood test?  	

Have you ever received a vaccine for COVID-19?  Some COVID-19 vaccines are given in 2 separate doses and some are given in one dose. Which kind of COVID-19 vaccine did you receive? The one-dose vaccine or the two-dose vaccine?

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Summary of select COVID questions from first few Stands of NHANES 2021 – 2022 
| Have you ever had COVID-19                                                                                 |       |
|------------------------------------------------------------------------------------------------------------|-------|
| Yes                                                                                                        | 11.0% |
| No                                                                                                         | 86.6% |
| Maybe                                                                                                      | 1.8%  |
| RF                                                                                                         | 0.1%  |
| DK                                                                                                         | 0.5%  |
| Ever been tested for COVID-19                                                                              |       |
| Yes                                                                                                        | 59.4% |
| No                                                                                                         | 40.3% |
| DK                                                                                                         | 0.3%  |
| Ever received a vaccine for COVID-19                                                                       |       |
| Yes                                                                                                        | 61.3% |
| No                                                                                                         | 38.5% |
| RF                                                                                                         | 0.2%  |
| Note: unweighted percentages; includes Dress Rehearsal Stand and first 3 Stands with SP questionnaire data |       |

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NHANES 2021 – 2022: Current Learnings

Overall changes to sampling, home interview, and MEC appear successful.

Some modifications were necessary: 

Adjusting MEC schedule due to lab constraints

Adjusting protocols based on new or updated policies (e.g., vaccination of federal contractors, updates to CDC COVID screener)

Challenges:

Hiring field positions 

Managing when staff become infected

Some scheduling challenges

Regional shortage of dry ice

Needs further assessment:

Value of multimode screening

Reasons for SP refusals at each stage of survey (i.e., screener, interview, and exam)

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Thank youFor further information please contact:Ryne PauloseRPaulose@cdc.gov

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