For basic information on the disease and how individuals can mitigate the spread, the following resources provide excellent information:

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1. COVID-19 TESTING

  • What is the definition of a "close contact?"

     

    Both When to Test Calculators are based on CDC guidelines. Current guidelines define a “close contact” as someone who was within six feet of an infected person for a total of at least 15 minutes over the course of 24 hours. One exception to that rule is applicable only to schools: Students who were between three and six feet of an infected person are not considered close contacts as long as they were in school and “correctly and consistently” wearing masks.

    CDC — Close contact definition 

  • What is follow-up testing, and how does it work?

     

    Follow-up testing is a critical part of pooled testing. In pooled testing, samples are gathered from multiple people and mixed together into a pool. Instead of testing each individual sample on its own, the lab tests the pool. If a pool tests positive, then at least one individual in the pool may be positive for COVID-19. When this happens, follow-up testing, sometimes referred to as “reflex testing” or “deconvolution,” is required. If follow-up testing isn’t possible, then the entire pool should isolate.

    In follow-up testing, each person or each sample in the positive pool is individually retested to determine which individual(s) in the positive pool are infected. The way follow-up testing happens depends in part on how and where the samples are pooled.

    The When to Test Calculator for Organizations identifies four testing strategies for follow-up testing a positive pool. Details on each strategy appear beneath the table below.

    Automatic

    Pooling Process: Individual samples are collected on-site and taken to an off-site lab. The lab creates the pools and tests the pooled samples using PCR.

    Follow-Up Testing Process: When a positive pool is identified, the lab automatically retests the individual samples that went into the pool using PCR.

    Pros and Cons

    • Eliminates need to re-collect individual samples.
    • Results are provided faster than other pooled testing strategies.
    • May be 2-3x more costly per test than rapid antigen and on-site PCR follow-up.

    On-Site Rapid Antigen

    Pooling Process: Individual samples are collected and pooled on-site. The pooled samples are taken to an off-site lab, which tests them using PCR.

    Follow-Up Testing Process: When a positive pool is identified, all individuals in the positive pool must be resampled. Individual follow-up tests are completed on-site, using rapid antigen tests.

    Pros and Cons

    • Faster than off-site PCR follow-up.
    • Likely to be least expensive option.
    • Requires trained staff on site.
    • Slightly less accurate than PCR follow-up.

    On-Site PCR

    Pooling Process: Individual samples are collected and pooled on-site. The pooled samples are taken to an off-site lab, which tests them using PCR.

    Follow-Up Testing Process: When a positive pool is identified, all individuals in the positive pool must be resampled. Individual follow-up tests are completed on-site, using rapid antigen tests.

    Pros and Cons

    • Faster than off-site PCR follow-up.
    • Less expensive than automatic or off-site PCR follow-up.
    • Requires PCR instruments and trained staff on site.
    • Highly accurate.

    Off-Site PCR

    Pooling Process: Individual samples are collected and pooled on-site. The pooled samples are taken to an off-site lab, which tests them using PCR.

    Follow-Up Testing Process: When a positive pool is identified, all individuals in the positive pool must be resampled. Samples are shipped to an off-site lab, where individual follow-up tests are completed with PCR.

    Pros and Cons

    • Slowest pooling option.
    • More expensive than on-site follow-up.
    • Highly accurate.

    For more information on pooled testing in schools, please download the When To Test K-12 Playbook.

  • What does Emergency Use Authorization (EUA) mean?

     

    In the US, the use of medical tests is regulated by the Food and Drug Administration (FDA). These tests can only be used in this country once they’ve undergone a long approval process. In early 2020, the US was in desperate need of tests for COVID-19; we needed them as soon as possible. For this reason, the US Secretary of Health and Human Services declared that the FDA could use Emergency Use Authorization to make COVID-19 tests available more quickly.

    As its name suggests, EUA is a seldom-used type of authorization which is only allowed during public-health emergencies. It enables the FDA to authorize the use of medical products (including tests) that haven’t undergone the long approval process, provided that “certain criteria are met.” At a minimum, the product must have known and potential benefits that outweigh its known potential risks. In addition, there must be “no adequate, approved, and available alternatives” to the product receiving the EUA.

     

    There are currently no COVID-19 tests that have complete approval from the FDA. Those that have EUA have undergone a shortened version of the approval process, which ensures that they meet the criteria mentioned above, among other requirements. The When to Test Calculator for Organizations assumes that your workplace or school is using a test that has received EUA.

    FDA — Emergency Use Authorization
     

  • What kinds of tests can be used for COVID-19 screening or diagnostic testing?

     

    Both kinds of testing can be done using either a PCR (also known as molecular) or antigen test.

    PCR tests look for pieces of the virus’s genetic material. They are the most accurate kind of test for COVID-19 currently available.

    Antigen tests look for viral proteins. They are slightly less accurate than PCR tests.

    Antibody tests (also known as serology tests) look for antibodies to SARS-CoV-2 (the virus that causes COVID-19). Those antibodies can come from a past COVID-19 infection or from a COVID-19 vaccine. This kind of test cannot be used to diagnose an active COVID-19 infection.

    CDC — Interim Guidance for Rapid Antigen Testing

  • What is confirmatory testing, and why would my organization need it?

     

    Confirmatory testing is done to make sure the results of a test are correct. In most cases, confirmatory testing is used to verify whether a negative result on a COVID-19 antigen test is accurate.

    If a test with a specificity of less than 99% comes back positive, especially in low-prevalence environments, confirmatory testing is also recommended. Asymptomatic screening programs are frequently supplemented by confirmatory testing because false positives are more common when screening asymptomatic individuals.

    CDC — Interim Guidance for Rapid Antigen Testing

  • What is the difference between point of care (POC) testing and lab-based testing?

     

    In point-of-care (POC) testing, all testing steps, including sampling and analysis, take place close to or near the patient. For the When to Test Calculators, this means that testing is completed either on-site at your organization’s location or in a health-care provider's office, at a testing site, or in your home. Point-of-care tests give you results quickly. Most of them are antigen tests, but some point-of-care PCR tests are available, as well.

    In lab-based or off-site testing, samples are gathered on-site at your organization or other testing location and are sent to a central lab for processing and analysis. Lab-based tests are generally PCR tests, which are highly accurate. However, they take longer to return results than point-of-care tests do. In some cases, the turnaround time of lab-based tests is not fast enough to prevent an outbreak in an organization.

    CDC — Guidance for COVID-19 Point-of-Care Testing

  • What is R0 (R-naught)?

     

    R0 (R-naught) is a measure of the average number of people who will contract a contagious disease from one infected person. It’s a measure of viral transmissibility, or how fast the disease is spreading.

    When R0 is exactly 1.0, it means that, on average, one infected person will infect one other person. When R0 is less than 1.0, it means that the spread of the disease is decreasing within the community. When R0is above 1.0, the spread of disease is increasing. The more transmissible a disease or disease variant is, the higher its R0.

    The When to Test Calculator for Organizations bases its default R0 on CDC estimates regarding the transmissibility of the most prevalent variant of COVID-19 in the US, which is currently the Delta variant. The Calculator's default R0 for Typical conditions reflects the CDC's low-end estimate of Delta's R0, while the default setting for Hotspot conditions reflects a higher-end estimate of Delta's R0. If you know which variant is most common in your area and wish to change the R0 in your scenarios to reflect that variant, click on "Show Advanced Settings," then "Main Calculator Settings,” and scroll down to "Estimated R0."

    CDC — US COVID-19 Cases Caused by Variants

    CDC — What You Need to Know about Variants

    World Health Organization — Tracking SARS-CoV-2 Variants

    Johns Hopkins Medicine — New Variants of Coronavirus

     

  • How do COVID-19 variants affect testing?

     

    The CDC and FDA, in partnership with the major testing laboratories, continue to carefully monitor the emergence of variants and how their genetic characteristics might affect testing.

    NOTE: As part of its calculations, the When to Test Calculator for Organizations includes a default measurement of how transmissible the virus is. That measurement is called R0 (“R-naught”) or the basic reproduction number for the virus. WhentoTest.org follows CDC guidance to set the Calculator’s default for R0. If you would like to set a specific R0 in your scenarios, you can do so under Advanced Settings: Main Calculator Settings.

    CDC — What You Need to Know About Variants

    CDC COVID — 19 Pandemic Planning Scenarios

    FDA Issues Alert Regarding SARS-CoV-2 Viral Mutation

  • What is pooled testing?

     

    Pooled testing, also known as pooling, is a way to make highly sensitive PCR testing more cost-effective. In pooled testing, samples are gathered from multiple people and mixed together into a pool. Instead of testing each individual sample on its own, the lab tests the pool, thus using fewer resources and lowering processing costs.

    If a pool tests negative, then all individuals in that pool are ‘clear’ or negative for COVID-19 and may continue to attend class, work, or other activities.

    If a pool tests positive, then at least one individual in the pool may be positive for COVID-19. When this happens, follow-up testing, sometimes referred to as “reflex testing” or “deconvolution,” is required. Follow-up testing can be done at a central lab or on-site.

    In follow-up testing, each person or each sample in the positive pool is individually retested to determine which individual(s) in the positive pool are infected. If follow-up testing isn’t possible, then the entire pool should isolate. Pooled testing should be done at a lab, using a PCR test that has Emergency Use Authorization (EUA) from the FDA. The lab’s pooling system should either have EUA or be internally validated.

    Pooled testing should be done at a lab, using a PCR test that has Emergency Use Authorization (EUA) from the FDA. The lab’s pooling system should either have EUA or be internally validated.

    CDC – Guidance for Use of Pooling Procedures

    FDA – Pooled Sample Testing

    Open and Safe Schools — Includes toolkit on how to start a pooled testing program at your school.
    When To Test K-12 Playbook for COVID-19

  • What is prevalence?

     

    For the purposes of the When To Test Calculators, prevalence is the percentage of individuals in a population who are infected with COVID-19 at any given moment. If there are 100 people in a building and one person has COVID-19, then the prevalence of COVID-19 in that building is 1%.

    The prevalence default settings for the When To Test Calculator for Organizations are 1% for typical conditions and 3% for hotspot conditions. To adjust these settings, click on the Show Advanced Settings button on the results page, open the Main Calculator Settings tab, and scroll down to the Prevalence settings (green arrows below).

    The When To Test Calculator for Individuals uses prevalence information that is estimated at the county level.