CDC Guidance for Expanded Screening Testing to Reduce Silent Spread of SARS-CoV-2

CDC Guidance for Expanded Screening Testing to Reduce Silent Spread of SARS-CoV-2
Updated Jan. 21, 2021

Updated Jan. 21, 2021

This interim guidance is based on what is currently known about the novel coronavirus (SARS-CoV-2) and coronavirus disease (COVID-19) as of the date of posting, December 1, 2020.

Guidance from the U.S. Centers for Disease Control and Prevention (CDC) are meant to supplement—not replace—any federal, state, local, territorial, or tribal health guidance. Implementation should be guided by what is feasible, practical, and acceptable, as well as tailored to the needs of each community or unique workplace environment. The intended audience is state, tribal, local, and territorial public health departments and their partners.

CDC will update this guidance as needed and as additional information becomes available.

Note: This document is intended to provide considerations for expanding screening testing for SARS-CoV-2, the virus that causes COVID-19 and does not dictate the determination of payment decisions or insurance coverage of such testing, except as may be otherwise referenced (or prescribed) by another entity or federal or state agency. CDC has no regulatory authority over testing; therefore, the information in this document is meant to assist health departments in making decisions rather than in establishing any regulatory requirements.

Persons with asymptomatic and presymptomatic infection are significant contributors to community SARS-CoV-2 transmission and occurrence of COVID-19. The following considerations are meant to help state, tribal, local, and territorial jurisdictions plan for expanded screening testing for SARS-CoV-2 to prevent or reduce silent spread of the virus. Jurisdictions should consider implementing an expanded screening testing strategy to rapidly identify people without symptoms (i.e., asymptomatically or presymptomatically infected with SARS-CoV-2) who are contributing to the silent spread of infection, because they are unaware that they are infectious. If testing resources are limited, expansion of testing of asymptomatic persons as described here might not be feasible.

This document:

  • includes considerations for groups to be prioritized for expanded screening testing;
  • provides indicators for levels of incidence and test positivity (past 7 days) in local communities that can help guide geographic surge testing and frequency;
  • outlines follow up steps for persons who test positive;
  • and emphasizes the importance of sustaining and reinforcing principal mitigation measures including wearing masks, hand hygiene, social distancing, and limiting all gatherings outside of the immediate household without significant mitigation efforts.

With the additional testing capacity available through antigen tests, rapid testing can be implemented to immediately isolate infected persons (both asymptomatic and symptomatic). Symptomatic persons and those who are close contacts of persons with SARS-CoV-2 infection, as well as surrounding persons whose exposure status is less certain in outbreak settings, remain prioritized for diagnostic testing.  Jurisdictions should assess feasibility in deciding whether to expand testing of asymptomatic persons as described here. Where possible and feasible, local jurisdictions should expand testing of persons without symptoms including sentinel surveillance of specific populations to identify specific geographic locations of community spread; this should be coupled with comprehensive community level mitigation efforts.

To reduce SARS-CoV-2 transmission, jurisdictions should consider expanding testing of persons without symptoms (with and without known exposure) to reduce asymptomatic (silent) spread in addition to comprehensive community-wide mitigation efforts and testing of individuals with symptoms consistent with COVID-19. All communities should test close contacts of cases (e.g., depending on case burden and available resources; close contacts should be tested immediately after identification as a contact, and if negative, could be tested again about 5-7 days after last exposure or immediately if symptoms develop during quarantine), and consider implementing a tiered approach to expand testing similar to the guidance for institutions of higher education, high-density critical infrastructure workplaces, select non-healthcare workplaces, and healthcare personnel.  This testing might reduce the 14-day quarantine of close contacts (for information on shorter quarantine times, see Check your local health department’s website for information about options in your area to possibly shorten this quarantine period.

Examples of groups to prioritize for expanded screening testing

These are not listed in a priority order. Jurisdictions can use these examples to guide their considerations as they develop local recommendations to prioritize select groups (examples are listed below) for expanded screening testing taking into account feasibility and costs. Jurisdictions might also consider sampling subgroups for screening testing initially to evaluate the need for more expanded screening testing in a particular group. In addition, expanded screening of asymptomatic persons should focus on groups (e.g. older adults, racial and ethnic minorities, people with disabilities,) that have been heavily impacted by COVID-19 to assure access and health equity.

Workers in high-density worksites or worksites with large numbers of close contacts (e.g., restaurant workers, transportation workers, grocery store workers)

Government workers with public interactions as part of their duties (e.g., post office)

Residents and staff in congregate settings* such as shelters serving the homeless and correctional facilities or residential settings serving persons with disabilities; workplaces that provide congregate housing (e.g., fishing vessels, offshore platforms, farmworker housing or wildland firefighter camps)

Students, faculty, and staff at institutions of higher education (including community colleges and technical schools)

Teachers and staff in K-12 schools and/or childcare settings

Persons who recently traveled and those who attended mass gatherings

First responders (e.g., police, fire, EMT) and healthcare personnel

*Nursing homes are also a priority group, with existing testing recommendations separate from the guidance in this document.

For communities with high incidence (see indicator table below), expanding screening testing could be considered for specific age groups (e.g., young adults) for whom increases have been documented early as incidence rises.

Type of tests to use for screening of asymptomatic persons

  • Nucleic acid amplification tests (NAAT) with turnaround times from sample collection to results reported as soon as possible (e.g., within 24–48 hours).
  • Rapid antigen tests (point of care, reporting results within ~30 minutes of sample collection)
    • Asymptomatic persons testing positive by rapid antigen tests should be confirmed by NAAT.
    • Symptomatic persons testing negative by rapid antigen tests should be confirmed by NAAT.
    • When the pretest probability for receiving positive test results for SARS-CoV-2 is elevated (e.g., in persons with a known COVID-19 exposure), a negative antigen test result should be confirmed by NAAT.
    • Rapid results can be critical to interrupting SARS-CoV-2 transmission, particularly when community transmission levels are high or in outbreak settings.
    • Performance characteristics of the specific test used in asymptomatic persons needs to be considered in establishing the protocol for confirmatory testing.

Frequency and Scope of Testing

  • The frequency of testing for asymptomatic persons in prioritized groups (but not known to be close contacts of a confirmed case) could be informed by the current community indicators for COVID-19 including cumulative incidence in the past 7 days and test positivity rate in addition to other known factors about the epidemiology of transmission in a particular community.
  • Frequency of testing could also be informed by the size of the workplace, residential setting, or gathering.
  • All communities should test close contacts of cases.
    • Depending on case burden and available resources, close contacts should be tested immediately after identification as a contact, and if negative, could be tested again about 5-7 days after last exposure or immediately if symptoms develop during quarantine.
  • Communities could consider implementing a tiered approach to expand testing to those who might have exposure even if not specifically identified as close contacts, analogous to the considerations for high-density critical infrastructure workplaces, institutions of higher education, and select non-healthcare workplaces. This expanded testing of contacts around cases will be particularly important for low incidence (green) areas.
  • Symptom screening should be conducted in addition to implementing any expanded screening testing. For students in grades K-12, parents, caregivers, or guardians should monitor their children for symptoms of infectious illness every day through home-based symptom screening. Persons with positive signs or symptoms consistent with COVID-19 should be referred for testing and medical evaluation if indicated.
  • If initial results indicate localized transmission in a selected group is high, more frequent screening of that group might be needed regardless of the community indicators.
Community indicators at the county level
(consider higher categorization based on either of the 2 indicators below) Low Moderate High Highest
Cumulative number of new cases per 100,000 persons within the last 7 days < 10 10 to 50 51-100 > 100
Percentage of viral tests that are positive during the last 7 days < 5% 5% to 7.9% 8% – 10% > 10.1 %
Categorization and actions
Low Focus on ensuring testing for all close contacts of cases and potentially expanding using a tiered approach to those who might have exposure
Moderate Weekly screening testing of select groups plus testing of close contacts
High Weekly or twice a week screening testing of select groups plus testing of close contacts
Highest Twice a week or more frequent screening testing for select groups plus testing of close contacts

Actions to follow up on positive tests

  • A SARS-CoV-2 positive test should result in:
    • Same-day notification to the Health Department of the test result and the participant’s identity and contact information.
    • A follow-up call, or text, to screen people with a positive test for new onset COVID-like illness symptoms including danger signs which might require referral to emergency services.
    • Instructions on when, where, and how to seek clinical care (e.g., call clinic and present during appointment while wearing a face covering, etc.).
    • Recommendation for immediate isolation for at least 10 days and self-monitoring of illness progression, plus information on confirmatory test results if conducted. If confirmatory NAAT test is negative, individual can be released from isolation.
    • Contact tracing to identify close contacts, recommend and help guide them to testing, ask them to self-monitor for symptoms, and quarantine for 14 days (for information on shorter quarantine times, see Check your local health department’s website for information about options in your area to possibly shorten this quarantine period.
      • As noted above, consideration can be given to testing close contacts (e.g., depending on case burden and available resources, testing immediately after identification as a contact, and if negative initially, testing again 5–7 days after last exposure).  For close contacts, CDC has recommended two options for health departments wishing to shorten quarantine (see: and endorses these as well the existing 14-day quarantine recommendation. CDC recognizes that quarantine shorter than 14 days balances reduced burden against a small possibility of spreading the virus. CDC will continue to evaluate new information and update recommendations as needed.
      • Employers are encouraged to implement flexible, non-punitive sick leave and supportive policies and practices. If close contacts who are critical infrastructure workers or healthcare workers return to work because it is necessary for continuity of operations, they should do so only if they remain asymptomatic, have ongoing symptom monitoring, use face masks, maintain social distancing, and there is appropriate disinfection of the workplace.

Principal mitigation measures

  • Increase messaging on mitigation strategies, including mask wearing, hand hygiene, and maintaining physical distance (social distancing). This messaging should be universal, including those with recent negative tests.
  • Deploy universal masking to cohorts of persons identified for expanded testing (may require distribution of masks to marginalized or hard-to-reach populations).
  • Increase social distancing and reduce crowding, especially within indoor environments.
  • Increase engineering controls (i.e., structural barriers) and improve ventilation in businesses, office buildings, schools, healthcare facilities, and congregate settings.
  • Ensure adequate supplies for proper hand hygiene and cleaning/disinfection of high-touch surfaces.
  • Consider incentives including to individuals or at a community or workplace level to increase compliance with mitigation measures:
    • Paid sick leave for isolation and quarantine.
    • Increased telework flexibility for workers in high risk groups when possible.
    • Wrap-around services for persons who are placed in isolation (positive SARS-CoV-2 test) or quarantine (for those who are close contacts), meaning provision of temporary housing, home delivery of food, and other essential supplies.

Protection of Personal Information

Where communities collect or use personal information from individuals for prioritization or other related purposes, communities should collect/create, handle, and store the information to avoid adverse impact on individuals’ privacy and in accordance with federal, state, and local laws and regulations.

Prevention of Discrimination

Communities should take steps to ensure that the group-focused prioritization for expanded testing does not inadvertently result in discrimination.