Those not up to date with their vaccines with negative results should remain in quarantinefor 5 days unless other guidance is given by the local, tribal, or territorial public health authority. At low levels of community circulation, the risk of false-positive test results will exceed the public health benefit. Correct interpretation of results from antigen tests confirmatory NAATs and other tests when indicated, is important. Pretest probability considers both the COVID-19 Community Level as well as the clinical context of the individual being tested. This overview describes current information on the types of tests used to detect SARS-CoV-2 infection and their intended uses, including to diagnose infection, screening testing to reduce the viruss spread by people who do not have symptoms, and to monitor trends in infection. Learn more Wastewater, also referred to as sewage, includes water from household/building use (i.e., toilets, showers, sinks) that can contain human fecal waste, as well as water from non-household sources (e.g., rainwater and industrial use), can be tested for RNA from SARS-CoV-2. official website and that any information you provide is encrypted The benefits of screening would be proportional to disease prevalence, with greater benefit from higher community risk. Science Brief: Indicators for Monitoring COVID-19 Community Levels and Making Public Health Recommendations.
Screening allows early identification and isolation of persons who are asymptomatic, pre-symptomatic, or have only mild symptoms and who might be unknowingly transmitting virus. CDC is not responsible for Section 508 compliance (accessibility) on other federal or private website. Most people with COVID-19 have mild illness and can recover at home without medical care. Unity Health Toronto (Schwartz); Departments of Medicine (Bogoch), and Laboratory Medicine and Pathobiology (McGeer), and Dalla Lana School of Public Health (Schwartz, McGeer), University of Toronto; Sinai Health System (McGeer); University Health Network (Bogoch), Toronto, Ont.
Linking to a non-federal website does not constitute an endorsement by CDC or any of its employees of the sponsors or the information and products presented on the website. Testing 23 times per week is suggested for optimal public health impact.20 In the UK, screening showed lower sensitivity when tests were performed by testers who were not health care workers than when they were performed by health care workers; however, the discrepancy disappeared over a 2-week period, which suggests that workers who are not trained in health care can be taught with experience to adequately perform swabs.16 Preprint research has shown that self-testing may have similar performance to swabs taken by professionals,21 and home-based use needs urgent evaluation to facilitate scalability and minimize biosafety concerns. Settings providing an essential service or manufacturing role, including schools, where direct close contact cannot be avoided, should be considered for such programs. Counties with a travel time of more than 20 minutes to a COVID-19 testing site had a higher percentage of the population that were from racial and ethnic minority groups, uninsured, and had lower population density (were rural).3 While access to testing may have improved since April 2020, travel time may still limit access to, and use of, testing services for those who have limited access to transportation and who live in areas with fewer public transit services and schedules. Clear guidance and messaging can mitigate the potential harms of false-negative test results and the impact of false-positive results.
Surveillance testing is primarily used to gain information at a population level, rather than an individual level, and generally involves testing of de-identified specimens. Diagnostic testingis intended to identify current infection in individuals and is performed when a person has signs or symptoms consistent with COVID-19, or is asymptomatic, but has recent known or suspected close contact exposure to SARS-CoV-2. Johansson MA, Quandelacy TM, Kada S, et al.. SARS-CoV-2 transmission from people without COVID-19 symptoms, Quantifying asymptomatic infection and transmission of COVID-19 in New York City using observed cases, serology, and testing capacity, Transmission heterogeneities, kinetics, and controllability of SARS-CoV-2. Evaluation of rapid testing programs will need to include the rate of detection of additional cases, estimates of cases avoided by the intervention, impact on workers, cost of isolation of those with false-positive test results and the possible impact of changed behaviour resulting from negative test results. More information is available, Recommendations for Fully Vaccinated People, Considerations for Testing in Different Scenarios, Public Health Surveillance Testing for SARS-CoV-2, comprehensive approach to reducing transmission, people who are up to date with their vaccines, In Vitro Diagnostics Emergency Use Authorizations, In healthcare facilities with an outbreak of SARS-CoV-2, multisystem inflammatory syndrome in children (MIS-C), Interim Clinical Considerations for Use of mRNA COVID-19 Vaccines Currently Authorized in the United States, pretest probability and the likelihood of positive and negative predictive values, false-positive results with antigen tests, false-negative results with molecular tests if a genetic variant of SARS-CoV-2, FAQs for healthcare providers who are using diagnostic tests in screening asymptomatic individuals, temporarily exercise enforcement discretion, required laboratories and testing facilities to report, other populations disproportionately affected, Duration of Isolation and Precautions for Adults with COVID-19, COVID-19 quarantine and isolation guidance, exposed to people with known or suspected COVID-19, CDC has provided options to shorten quarantine, Options to Reduce Quarantine for Contacts of Persons with SARS-CoV-2 Infection Using Symptom Monitoring and Diagnostic Testing, Performing Broad-Based Testing for SARS-CoV-2 in Congregate Settings, Accumulating evidence supports ending isolation and precautions. Regardless of their vaccination status, people who have had a close contact exposure with someone known or suspected of having COVID-19 should be tested at least 5 days after the incident, if possible, or earlier if symptoms develop. Laboratory tests fall into 2 main categories: diagnostic and screening tests. Most peoplewith a history of test-confirmed COVID-19 who remain symptom-free after recovery do not need to retest or quarantine if another exposure occurs within 90 days after their initial infection. Overview of Testing for SARS-CoV-2, the virus that causes COVID-19, Centers for Disease Control and Prevention. The U.S. Department of Health and Human Services has required laboratories and testing facilities to reportrace and ethnicity data to health departments, in addition to other data elements, for individuals tested for SARS-CoV-2 or diagnosed with COVID-19. Identifying 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 can help reduce the spread of SARS-CoV-2 in communities, workplaces, and schools when these close contacts quarantine themselves. Saving Lives, Protecting People, Given new evidence on the B.1.617.2 (Delta) variant, CDC has updated the, The White House announced that vaccines will be required for international travelers coming into the United States, with an effective date of November 8, 2021. Depending on the time when someone was infected and the timing of the test, the test might not detect antibodies in someone with a current infection. For guidance on quarantine and testing of people who are up to date with their vaccines, please visit COVID-19 Quarantine and Isolation. All of the authors gave final approval of the version to be published and agreed to be accountable for all aspects of the work. This is especially important when the. People without symptoms and without known exposure to COVID-19 do not need to quarantine while awaiting screening test results. Public health surveillance is intended to monitor population-level burden of disease, or to characterize the incidence and prevalence of disease. Unvaccinated persons with asymptomatic or pre-symptomatic infection are frequent contributors to community SARS-CoV-2 transmission and occurrence of COVID-19 illness. A subsequent evaluation in the UK found that the Innova rapid antigen test detected more than 90% of samples with Ct values for RTPCR less than 25.5 as positive,15 and a program of rapid antigen testing for staff and visitors in long-term care homes was implemented.16. Positive and negative predictive values of NAAT and antigen tests vary depending upon the pretest probability. Preprint research has reported on the findings of Slovakias 2 rounds of countrywide mass testing in October and November 2020; this involved 60 000 (20 000 medical and 40 000 nonmedical) staff and 5 million rapid antigen tests.14 In the first and second rounds, the rate of positivity was 1.01% (range across counties 0.13% to 3.22%) and 0.62% (range 0.28% to 1.65%), respectively, an adjusted decrease in SARS-CoV-2 infections of 61% (95% confidence interval 50%70%) from the first to second round. Some adults with severe illness may produce replication-competent virus beyond 10 days that may warrant extending duration of isolation and precautions. Viral tests can also be used as screening tests to reduce the transmission of SARS-CoV-2 by identifying infected persons who need to isolate from others. Racial and ethnic minority groups and other populations disproportionately affected by COVID-19, Teachers and staff in K-12 schoolsand/or childcare settings, Students, faculty, and staff at institutions of higher education(including community colleges and technical schools), Workers in high-density worksitesor worksites with large numbers of close contactto co-workers or customers (restaurant workers, transportation workers, grocery store workers), Government workers with public interactions as part of their duties (post office workers), First responders (police, fire, emergency medical technician [EMT]) and healthcare personnel, Residents and staff in congregate settings, such as shelters serving the homeless and correctional and detention facilities or residential settings, such as nursing homesor those serving persons with disabilities; workplaces that provide congregate housing (fishing vessels, offshore platforms, farmworker housing or wildland firefighter camps); and military facilities (barracks), Persons who recently traveled, either domestically or internationally.
Larremore DB, Wilder B, Lester E, et al.. Test sensitivity is secondary to frequency and turnaround time for COVID-19 screening. For more information, see the Antigen Test Algorithm. These results represent a snapshot of the time around specimen collection and could change if the same test was performed again in one or more days. More information is available, Travel requirements to enter the United States are changing, starting November 8, 2021. Frequent testing (12 times per week) combined with other risk reduction strategies, contributed to low case rates in university settings. The goal is not to eliminate individual risk but to reduce population-level risk. People with symptoms should continue to seek a diagnostic PCR test. These results represent a snapshot of the time around specimen collection and could change if tested again in one or more days. 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. Racial and ethnic disparities in test site distribution have been found.4Other factors that may affect both access to, and use of, testing services include: Delays in testing may also delay seeking care when sick as well as delays in self-isolation or implementing other mitigation measures that could reduce the spread of the virus to others. Opponents of the use of rapid antigen tests for screening have argued that the their lower diagnostic sensitivity when compared with RTPCR makes these tests unsuitable for use because false-negative results may cause potential harms owing to a substantial proportion of infections not being detected.17 This concern arises from the belief that a false-negative test result in a person with a high viral load will be associated with behaviour change that will increase infection risk in the community. Public health surveillance testing may sample a certain percentage of a specific population to monitor for increasing or decreasing prevalence or to determine the population effect from community interventions, such as social distancing. This guidance also includes considerations for: This information is intended for use by healthcare providers, public health professionals, and those organizing and implementing testing in non-healthcare settings, such as schools, workplaces, and congregate housing. Results from NAATs are considered the definitive result when there is a discrepancy between the antigen and NAAT test. 8600 Rockville Pike In addition, completeness of race and ethnicity data is an important factor in understanding the impact the virus has on racial and ethnic minority populations. Such screening programs will not end the COVID-19 pandemic but, if carefully implemented, could provide an additional layer of safety to current public health strategies by allowing the identification of asymptomatic, presymptomatic and paucisymptomatic infectious individuals, and empowering people to make informed decisions about their own behaviour to reduce the spread of COVID-19. Antigen tests are immunoassays that detect the presence of a specific viral antigen. FDA has provided a list of FAQs for healthcare providers who are using diagnostic tests in screening asymptomatic individuals, and the Centers for Medicare & Medicaid Services will temporarily exercise enforcement discretionto enable the use of antigen tests that are not currently authorized for use in asymptomatic individuals for the duration of the COVID-19 public health emergency under the Clinical Laboratory Improvement Amendments of 1988 (CLIA). There are antigen tests available for at-home testing (self-testing), at the point of care, or in a laboratory. These examples are not listed in a priority order. NAATs have detected SARS-CoV-2 RNA in some peoples respiratory specimens long after they have recovered from COVID-19 (>3 months). After applying a sample from a nasal or nasopharyngeal swab, if antigen is present it will bind to the antibody and generate a coloured line on the device, similar to a home pregnancy kit or rapid test for malaria.7. This expansion ensures that wait times both for testing and reporting of results are decreased, helping limit the spread of SARS-CoV-2. Accessibility Serial testing (within cohorts) with rapid isolation of infected individuals may facilitate re-opening of businesses, communities, and schools (in-person instruction in K-12 schools. More meaningful than test accuracy is the extent to which rapid antigen testing identifies cases of COVID-19 during the infectious period and whether ongoing transmission is reduced. Increase public messaging about the importance of testing and communicate these messages in multiple languages and venues, particularly in communities at higher risk and disproportionately impacted by the virus. Specific age groups (e.g., young adults) for whom increases in COVID19 have been documented early as incidence rises, especially in areas where COVID-19 Community Levelis high (Table 2). In addition, it is not currently known whether a positive antibody test result indicates immunity against SARS-CoV-2; therefore, at this time, antibody tests should not be used to determine if an individual is immune against reinfection. No other competing interests were declared. The Centers for Disease Control and Prevention (CDC) cannot attest to the accuracy of a non-federal website. Some strategies to achieve this goal include: Positive test results using a viral test (NAAT, antigen or other tests) in persons with signs or symptoms consistent with COVID-19 indicate that the person has COVID-19, independent of vaccination status of the person. Introduction to Public Health Surveillance, multistate assessment of SARS-CoV-2 seroprevalence in blood donors, COVID-19-Associated Hospitalization Surveillance Network (COVID-NET), National Wastewater Surveillance System (NWSS), CDCs Diagnostic Multiple Assay for Flu and COVID-19 at Public Health Laboratories and Supplies, Infection Prevention and Control Recommendations for Healthcare Personnel, Interim Guidelines for COVID-19 Antibody Testing, Performing Facility-Wide Testing in Nursing Homes, Antigen Testing for Screening in Non-Healthcare Workplaces, https://www.epi.org/publication/black-workers-covid/, National Center for Immunization and Respiratory Diseases (NCIRD), Post-Vaccination Considerations for Workplaces, Decontamination & Reuse of N95 Respirators, Purchasing N95 Respirators from Another Country, Powered Air Purifying Respirators (PAPRs), Post-Vaccine Considerations for Residents, U.S. Department of Health & Human Services, New COVID-19 admissions per 100,000 population (7-day total), Percent of staffed inpatient beds occupied by COVID-19 patients (7-day average), Added Health Equity language for access of testing. CDC is working with state, local, territorial, academic, and commercial partners to conduct surveillance to better understand COVID-19 in the United States and recently conducted a multistate assessment of SARS-CoV-2 seroprevalence in blood donors. This guidance has been developed based on what is currently known about SARS-CoV-2 infection and COVID-19 and is subject to change as additional information becomes available. Performance of an antigen-based test for asymptomatic and symptomatic SARS-CoV-2 testing at two university campuses Wisconsin, SeptemberOctober 2020. Information to help public health departments and healthcare providers prepare for expanded viral testing in facilities after known or suspected SARS-CoV-2 exposure or in areas where the COVID-19 Community Level is high (Table 2) is available in CDCs Performing Broad-Based Testing for SARS-CoV-2 in Congregate Settings. Institutes of higher education with the resources to implement wastewater surveillance should develop a wastewater surveillance strategy in consultation with local public health authorities. Revised to align with CDC recommendations for fully vaccinated individuals, Expansion on the description of categories of tests, choosing a test, and addition of intended uses of testing, Addition of health equity considerations related to testing, including discussion on ensuring equitable testing access and availability, Discussion on expanded availability to, and use of, screening tests to reduce asymptomatic spread, Discussion on testing of vaccinated individuals and interpretation of test results, Inclusion of links to setting-specific testing guidance, Due to the significance of asymptomatic and pre-symptomatic transmission, this guidance further reinforces the need to test asymptomatic persons, including, Diagnostic testing categories have been edited to focus on testing considerations and actions to be taken by individuals undergoing testing, Except for rare situations, a test-based strategy is no longer recommended to determine when an individual with a SARS-CoV-2 infection is no longer infectious (i.e., to discontinue Transmission-Based Precautions or home isolation), Added screening to possible testing types, Removed examples please refer to setting specific guidance. For more information, see the Antigen Test Algorithm. Staffing and logistical challenges are substantial; governments will need to recognize that the cost of these programs will add to rather than replace the costs of current PCR testing and that program costs may substantially exceed test costs. One study found that in April 2020, the median travel time to a COVID-19 testing site was 20 minutes. If a person has received a COVID-19 vaccine, it does not affect the results of their SARS-CoV-2 viral tests (nucleic acid amplification tests [NAAT], antigen or other tests). To receive email updates about COVID-19, enter your email address: CDC has updated select ways to operate healthcare systems effectively in response to COVID-19 vaccination. Before It does not address issues regarding payment for or insurance coverage of such testing. Data from wastewater testing are not meant to replace existing COVID-19 surveillance systems. In the context of COVID-19, the goal of screening by rapid antigen testing is to increase the detection of asymptomatic or presymptomatic infection and reduce onward transmission of SARS-CoV-2. A report from the Office of the Auditor General of Ontario indicated that the average time from specimen collection to the start of case and contact management was 4.25 days.6 In this scenario, for patients who seek testing on their first day of symptoms, on average, contact tracing begins only once virtually all transmissions have occurred and after contacts have started to transmit to others. Although less than 10% of people in the UK suggested that their behaviour might change to some degree after a negative rapid test, it is not clear that this degree of change would result in a substantial increase in transmission.18 Similar hypotheses have historically been put forward for other public health interventions for example, arguing that having a negative result for an HIV test would result in higher-risk sexual behaviours, but these have not been confirmed.19 Although behaviour change owing to screening programs requires evaluation, if appropriate and clear communication is conveyed to the public on the meaning of a negative result for a SARS-CoV-2 rapid test, it is unlikely to result in widespread untoward compensatory behaviour change. Studieshave not found evidence that clinically recovered adults with persistence of viral RNA have transmitted SARS-CoV-2 to others. *The decreased sensitivity of antigen tests might be offset if the POC antigen tests are repeated more frequently (i.e., serial testing at least weekly). Negative test results in persons with known SARS-CoV-2 exposure suggest no current evidence of infection. See: Contact tracing assessment of COVID-19 transmission dynamics in Taiwan and risk at different exposure periods before and after symptom onset. Surveillance testing is performed on de-identified specimens, and, thus, results are not linked to individual people. Antigen tests are most sensitive in the early stages of infection when viral loads are high and have decreasing sensitivity as disease progresses and when transmission may be less likely. Most are less expensive than NAATs and can provide results in minutes, making them useful in screening programs to quickly identify persons who are likely to have COVID-19. Testing persons as a result of contact tracing efforts.
Even with ideal public health resources for testing and tracing, the strategy of testing only symptomatic cases will not identify many of the contacts before they transmit infection. For guidance on quarantine and testing of people who are up to date with their vaccines, please visit COVID-19 Quarantine and Isolation. Employers, community-based, and faith-based organizations can be important partners to increase the number of free, community-based testing sites. Lindner AK, Nikolai O, Rohardt C, et al.. SARS-CoV-2 patient self-testing with an antigen-detecting rapid test: a head-to-head comparison with professional testing [preprint], Support for self-isolation is critical in COVID-19 response, CMAJ : Canadian Medical Association Journal, https://creativecommons.org/licenses/by-nc-nd/4.0/, www.cmaj.ca/lookup/doi/10.1503/cmaj.202827, www.auditor.on.ca/en/content/specialreports/specialreports/COVID-19_ch3testingandtracing_en20.pdf, www.who.int/diagnostics_laboratory/eual/eul_0564_032_00_panbi_covid19_ag_rapid_test_device.pdf, www.ox.ac.uk/sites/files/oxford/media_wysiwyg/UK%20evaluation_PHE%20Porton%20Down%20%20University%20of%20Oxford_final.pdf, www.gov.uk/government/publications/evidence-on-the-accuracy-of-lateral-flow-device-testing/evidence-summary-for-lateral-flow-devices-lfd-in-relation-to-care-homes, https://blogs.bmj.com/bmj/2021/01/12/covid-19-government-must-urgently-rethink-lateral-flow-test-roll-out/. and transmitted securely. Frequent rapid antigen testing is a scalable public health tool that can effectively identify asymptomatic and paucisymptomatic people with SARS-CoV-2 infection and improve contact tracing and control of outbreaks. Screening testing can improve detection of SARS-CoV-2. See additional guidance to facilitate implementation of, Revised to align with CDCs updated recommendations on, Revised to align with CDC recommendations for. Public health surveillance testing is intended to monitor community- or population-level outbreaks of disease or to characterize the incidence and prevalence of disease. Chapter 3: special report on laboratory testing, case management and contact tracing, Viral kinetics of SARS-CoV-2 over the preclinical, clinical, and postclinical period, Predicting infectious SARS-CoV-2 from diagnostic samples, Antigen-based testing but not real-time polymerase chain reaction correlates with severe acute respiratory syndrome coronavirus 2 viral culture. CDC twenty four seven. Nasal, Nasopharyngeal, Oropharyngeal, Sputum, Saliva, Varies by test, but generally high for laboratory-based tests and moderate-to-high for POC tests, Varies depending on the course of infection, but generally moderate-to-high at times of peak viral load*, Most 1-3 days. For more information on how COVID-19 Community Levels are calculated, please see Science Brief: Indicators for Monitoring COVID-19 Community Levels and Making Public Health Recommendations. Note: This document provides guidance on the different types of viral tests for SARS-CoV-2 available in the United States and their intended uses. For guidance on quarantine after a negative test, visit COVID-19 Quarantine and Isolation. Although there can be substantial variability of Ct values between different PCR assays and quantification of viral load is difficult and expensive to do, Ct values provide a semiquantitative assessment of viral load, with lower Ct values representing higher viral loads. In healthcare facilities with an outbreak of SARS-CoV-2, recommendations for viral testing of healthcare providers, residents, and patients (regardless of their vaccination status) remain unchanged.
Because of the performance characteristics of antigen tests, it may be necessary to confirm some antigen test results (a negative test in persons with symptoms or a positive test in persons without symptoms) with a laboratory-based NAAT.
Bethesda, MD 20894, Web Policies A robust and responsive testing infrastructure is essential to the success of stopping the spread of SARS-CoV-2, the virus that causes COVID-19. ^ Costs for: NAATs Thus, when screening large numbers of persons (e.g., a well-defined cohort) without known or suspected exposure to SARS-CoV-2, test sensitivity may be less critical than whether the test can be performed more frequently and provide rapid results with immediate isolation of infected individuals.9Outbreak prevention and control are increasingly thought to depend largely on the frequency of testing and the speed of reporting (an advantage of antigen tests) and is only marginally improved in the context of serial tests by the higher test sensitivity of NAATs. In screening settings where antigen tests are used on asymptomatic people, laboratory-based confirmatory NAAT testing may be needed for certain individuals who test positive. A negative antigen test in persons with signs or symptoms of COVID-19 should be confirmed by NAAT, a more sensitive test. On some school campuses (e.g., institutes of higher learning), unvaccinated students may be tested upon arrival on campus or upon return from extended breaks.