Considerations for testing in different scenarios

Diagnostic testing

Testing persons with signs or symptoms consistent with COVID-19

Employers may consider conducting daily in-person or virtual health checks (e.g., symptom and temperature screening) to identify employees with signs or symptoms consistent with COVID-19 before they enter a facility, in accordance with CDC’s Guidance for Businesses and Employers Responding to Coronavirus Disease 2019 (COVID-19). Employers should follow guidance from the EEOCexternal icon  regarding confidentiality of medical records from health checks.

Vaccinated and unvaccinated workers with COVID-19 symptoms should be immediately separated from other employees, customers, and visitors, and sent home or to a healthcare facility, depending on how severe their symptoms are, and follow CDC guidance for caring for oneself. To prevent stigma and discrimination in the workplace, make employee health screenings as private as possible. CDC recommends that anyone with signs or symptoms of COVID-19 be tested and follow the advice of their healthcare provider. Waiting for test results prior to returning to work is recommended to keep potentially infected workers out of the workplace.

Employers are encouraged to implement flexible sick leave and supportive policies and practices as part of a comprehensive approach to prevent and reduce transmission among employees.

Positive test results using a viral test (NAAT or antigen) in persons with signs or symptoms consistent with COVID-19 indicate that the person has COVID-19. A negative antigen test in persons with signs or symptoms of COVID-19 should be confirmed by a laboratory-based NAAT, a more sensitive test. Results from NAATs are considered the definitive result when there is a discrepancy between the antigen and NAAT test. For more information, see the Antigen Test Algorithm pdf icon [458 KB, 1 Page]. Positive test results should be interpreted to indicate that a person has COVID-19 and should not come to work and should isolate at home. Decisions to discontinue isolation for workers with COVID-19 and allow them to return to the workplace may follow either a symptom-based, time-based, or a test-based strategy (see Testing to determine resolution of infection below).

Testing asymptomatic persons with recent known or suspected exposure to SARS-CoV-2

Case investigation is typically initiated when a health department receives a report from a laboratory or testing site of a positive SARS-CoV-2 viral test result, or a report from a healthcare provider of a patient with a confirmed or probable diagnosis of COVID-19pdf icon external icon .

In general, fully vaccinated workers with no COVID-like symptoms do not need to quarantine or be tested following an exposure to someone with suspected or confirmed COVID-19. However, those who work in congregate settings or other high-density workplaces (e.g., meat and poultry processing and manufacturing plants) should be tested after an exposure; however, they do not need to quarantine. For more guidance on quarantine and testing of fully vaccinated people, please visit Interim Public Health Recommendations for Fully Vaccinated People.

Viral testing is recommended for all unvaccinated close contacts (people who have been within 6 feet for a combined total of 15 minutes or more during a 24-hour period) of persons with COVID-19. Because of the potential for asymptomatic and pre-symptomatic transmission of SARS-CoV-2, it is important that unvaccinated individuals exposed to people with known or suspected COVID-19 be quickly identified and quarantined. Viral testing with NAATs or antigen tests can detect if these individuals are currently infected. The health department may ask the employer for assistance in identifying close contacts of the worker. Employers are encouraged to work with public health departments investigating cases of COVID-19 and tracing contacts to help reduce the spread of SARS-CoV-2 in their workplaces and communities.

Because there may be a delay between the time a person is exposed to the virus and the time that virus can be detected by testing, early testing after exposure at a single time point may miss many infections. Testing that is repeated at different points in time, also referred to as serial testing, is more likely to detect infection among close contacts of a COVID-19 case than testing done at a single point in time. Viral testing is recommended for close contacts of persons with COVID-19 who should be tested immediately after being identified, and if negative, tested again in 5–7 days after last exposure or immediately if symptoms develop during quarantine.

While CDC continues to recommend a 14-day quarantine for unvaccinated individuals who are close contacts of a person with COVID-19, viral testing may also be used as part of an option to shorten the quarantine period. Local public health authorities determine and establish the quarantine options for their jurisdictions. Shortening quarantine may increase willingness to adhere to public health recommendations. However, shortened quarantines may be less effective in preventing transmission of COVID-19 than the currently recommended 14-day quarantine. In jurisdictions with shortened quarantine options, workplaces with higher risk of SARS-CoV-2 introduction or transmission, or with potential for greater negative impact if employees become infected SARS-CoV-2 (see Types of workplaces below), can consider restricting workers from entering the workplace until 14 days after their exposure.

Testing may also be considered for unvaccinated persons who might have been in close contact with persons diagnosed with COVID-19 in collaboration with the local health department if resources permit. A risk-based approach to testing possible contacts of a person with confirmed COVID-19 may be applied. Such an approach should take into consideration the likelihood of exposure, which is affected by the characteristics of the workplace and the results of contact investigations. In some settings, expanded screening testing (i.e., testing beyond individually identified close contacts to those who are possible close contacts), such as targeting workers who worked in the same area and during the same shift, may be considered as part of a strategy to control the transmission of SARS-CoV-2 in the workplace. High-risk settings that have demonstrated potential for rapid and widespread dissemination of SARS-CoV-2 include:

• High-density critical infrastructure workplaces, where workers are in the workplace for long periods (e.g., for 8–12 hours per shift) and have prolonged close contact with coworkers
• Workplaces where employees live in congregate settingsexternal icon  (e.g., fishing vessels, offshore oil platforms, farmworker housing, or wildland firefighter camps)
• Workplaces with populations at risk for severe illness if they are infected, such as homeless shelters and workplaces with older workers

After a case of COVID-19 has been identified in a high-density critical infrastructure workplace, where workers are in prolonged close contact, NAAT or antigen testing can be used to diagnose infection in workers with known or suspected exposure to SARS-CoV-2. Employers are encouraged to consult with state, local, territorial, and tribal health departments to help inform decision-making about expanded screening testing.

If employees are tested after close contact or suspected close contact with someone who has a confirmed or probable diagnosis of COVID-19, care should be taken to inform these employees of their possible exposure to SARS-CoV-2 in the workplace while maintaining confidentiality of the individual with COVID-19, as required by the ADAexternal icon  and consistent with EEOC guidance regarding What You Should Know About COVID-19 and the ADA, the Rehabilitation Act, and Other EEO Lawsexternal icon .

Testing to determine resolution of infection

The decision to end isolation and return to the workplace for employees with suspected or confirmed SARS-CoV-2 infection should be made in the context of clinical and local circumstances. NAATs have detected SARS-CoV-2 RNA in some recovered people’s respiratory specimens for up to 3 months after illness onset but without direct evidence that virus that can replicate or cause disease. Consequently, evidence supports a time-based and symptom-based strategy to determine when to discontinue isolation or other precautions rather than a test-based strategy. For persons who are severely immunocompromised, a test-based strategy could be considered in consultation with infectious disease experts. For all others, a test-based strategy is no longer recommended except to discontinue isolation or precautions earlier than would occur under the symptom-based strategy.

Under the ADA, employers are permitted to require a healthcare provider’s noteexternal icon  to verify that employees are healthy and able to return to work. However, as a practical matter, employers should be aware that healthcare provider offices and medical facilities may be extremely busy during periods when community COVID-19 indicators are in the moderate to high categorizations (Table 2) and may not be able to provide such documentation in a timely manner. In such cases, employers should consider not requiring a healthcare provider’s note for employees who are sick to validate their illness, qualify for sick leave, or to return to work. Most people with COVID-19 have mild illness, can recover at home without medical care, and can follow CDC recommendations to determine when to discontinue isolation and return to the workplace.

Screening testing

Testing asymptomatic persons without known or suspected exposure to SARS-CoV-2 for early identification, isolation, and disease prevention

When to consider screening testing

Screening testing of asymptomatic workers without known or suspected exposure to SARS-CoV-2 in select non-healthcare settings may be useful to detect COVID-19 early and stop transmission quickly, particularly in areas with community COVID-19 indicators in the moderate to high categorizations (Table 2, Table 3). Screening testing can be used in addition to symptom and temperature checks, which will miss asymptomatic or presymptomatic contagious workers. Persons with asymptomatic or presymptomatic SARS-CoV-2 infection are significant contributors to SARS-CoV-2 transmission.

In general, fully vaccinated workers should continue to follow employer guidance on screening testing. Please see Interim Public Health Recommendations for Fully Vaccinated People for more information.

Types of workplaces

Workplace settings for which screening testing of workers should be considered include:

• Workplaces at increased risk of introduction of SARS-CoV-2 (e.g., workplaces where workers are in close contact with the public, such as restaurants or salons, or workplaces in communities with moderate to high transmission)
• Workplaces where there is a higher risk of SARS-CoV-2 transmission (e.g., workplaces where physical distancing is difficult and workers might be in close contact, such as manufacturing or food processing plants, or workplaces that provide congregate housing for employees such as fishing vessels, offshore oil platforms, farmworker housing or wildland firefighter camps)
• Workplaces where SARS-CoV-2 infection among employees will lead to greater negative impact, such as
  • Workplaces in remote settings where medical evaluation or treatment may be delayed
  • Workplaces where continuity of operations is a high priority (e.g.,critical infrastructure sectorsexternal icon )
  • Workplaces with a high proportion of employees at increased risk for severe illness

Frequency of screening testing

Approaches may include initial testing of all workers before entering a workplace, periodic testing of workers at regular intervals, targeted testing of new workers or those returning from a prolonged absence (such as medical leave or furlough), or some combination of approaches. Given the incubation period for COVID-19 (up to 14 days), CDC recommends conducting screening testing at least weekly. Employers may find the following factors helpful to consider when determining the interval for periodic testing:

• The availability of testing, turnaround time, and cost
• The latency time period between exposure and development of a positive SARS-CoV-2 viral test
• Type of workplaces
• Level of community transmission (Table 2, Table 3)
• How many employees tested positive during previous rounds of testing
• Relevant experience with outbreaks at the workplace

Serial testing used in a screening program could identify workers with SARS-CoV-2 infection, and thus help prevent or reduce further transmission, which is an occupational health measure of great importance in the types of workplaces mentioned above. Outbreak prevention and control is increasingly being thought to depend largely on the frequency of testing and the speed of reporting (an advantage of antigen tests) and is only marginally improved by the higher test sensitivity of  NAATs. Serial testing, if implemented, should be integrated as a component of the comprehensive workplace program and not a substitute for other measures, such as COVID-19 vaccination, social distancing, mask wearing, hand hygiene, and cleaning and disinfection. Engineering controls and improved ventilation in settings such as office buildings and schools are also important.

Interpretation of screening SARS-CoV-2 test results

For screening testing, some antigen test results should be considered presumptive (preliminary results). A positive antigen screening test result should be considered presumptive when the pretest probability (likelihood that the person being tested actually has the infection) for COVID-19 is low or moderate for the purpose of making a clinical diagnosis (e.g., a worker who is asymptomatic and has no known exposures to COVID-19). Asymptomatic employees who have a positive antigen screening test result should undergo a confirmatory NAAT. They should not come to work and should quarantine during confirmatory testing.

According to test manufacturers, negative antigen tests results are presumptive for the purpose of making a clinical diagnosis. A negative antigen screening test result does not need to be followed by confirmatory testing if the pretest probability is low or serial antigen testing will be performed.

NAATs do not need to be routinely repeated for confirmation. Employees with a positive NAAT result should not come to work and should isolate at home. A negative NAAT result is interpreted as no evidence of SARS-CoV-2 infection at the time when the testing sample was collected. Employees who test negative should continue to take steps to protect themselves and others.

State, local, territorial, and tribal health departments may be able to provide assistance on any local context or guidance impacting the workplace. Before testing a large proportion of asymptomatic workers without known or suspected exposure, employers are encouraged to have a plan in place for how they will ensure access to clinical evaluation and confirmatory testing when needed, ensure test results are reported to public health departments, modify operations based on test results, collaborate with public health departments in workplace case investigation and contact tracing, and manage a higher risk of false positive results in a low prevalence population.

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Indicators should be calculated for counties or core based statistical areas, although in rural areas with low population density, multiple jurisdictions might need to be combined to make the indicators more useful for decision-making. The indicators listed can be found by county on CDC’s COVID Data Tracker Website under “county view”.

@ If the two indicators suggest different transmission levels, the higher level should be selected.

* Number of new cases in the county (or other administrative level) in the last 7 days divided by the population in the county (or other administrative level) and multiplying by 100,000.

† Number of positive tests in the county (or other administrative level) during the last 7 days divided by the total number of tests resulted in the county (or other administrative level) during the last 7 days. Calculating Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Laboratory Test Percent Positivity: CDC Methods and Considerations for Comparisons and Interpretation.

Table 3. Potential Actions based on Community Indicator Level

References

1. Chin ET, Huynh BQ, Chapman LAC, Murrill M, Bash S, Lo NC. Frequency of routine testing for Coronavirus Disease 2019 (COVID-19) in high-risk healthcare environments to reduce outbreaks. Clin Infect Dis: 26 October 2020. https://doi.org/10.1093/cid/ciaa1383external icon
2. Denny TN, Andrews L, Bonsignori M, Cavanaugh K, Datto MB, Deckard A, DeMarco CT, DeNaeyer N, Epling CA, Gurley T, Haase SB, Hallberg C, Harer J, Kneifel CL, Lee MJ, Louzao R, Moody MA, Moore Z, Polage CR, Puglin J, Spotts PH, Vaughn JA, Wolfe CR. Implementation of a pooled surveillance testing program for asymptomatic SARS-CoV-2 infections on a college campus — Duke University, Durham, North Carolina, August 2–October 11, 2020. MMWR Morb Mortal Wkly Rep 2020;69(46):1743–1747. https://doi.org/10.15585/mmwr.mm6946e1external icon
3. Grassley NC, Pons-Salort M, Parker EPK, White PJ, Feruson NM; Imperial College COVID-19 Response Team.  Comparison of molecular testing strategies for COVID-19 control: a mathematical modelling study. Lancet Infect Dis 2020; 20(12):1381–1389. https://doi.org/10.1016/S1473-3099(20)30630-7external icon
4. Kucirka LM, Lauer LA, Laeyendecker O, Boon D, Lessler J. Variation in false-negative rate of reverse transcriptase polymerase chain reaction–based SARS-COV-2 tests by time since exposure. Ann Int Med 2020;173(4):262–267. https://doi.org/10.7326/M20-1495external icon
5. Larremore DB, Wilder B, Lester E, Shehata S, Burke JM, Hey JA, Tambe M, Mina MJ, Parker R. Test sensitivity is secondary to frequency and turnaround time for COVID-19 screening.  Sci Adv 2021;7(1):eabd5393. https://doi.org/10.1126/sciadv.abd5393external icon

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