āBackground
Diagnostic testing for COVID-19 identifies infected people. This is important to help guide infected people to appropriate treatment. It also offers the opportunity to reduce forward transmission of the virus by isolating infected people and notifying close contacts of their exposure.
Testing is just one layer in a multi-layered approach to COVID-19 harm reduction, which also includes vaccination, mask wearing, improved ventilation, treatment, and respiratory and hand hygiene.
Additional details can be found within the California Department of Public Health (CDPH) guidance on more specific testing recommendations in certain settings.
In the workplace, employers and employees are subject to either the Cal/OSHA COVID-19 Prevention Non-Emergency Regulations or, in some workplaces, the Cal/OSHA Aerosol Transmissible Diseases (ATD) Standard (PDF). Those regulations should be consulted for additional applicable requirements.
Additional information about Cal/OSHA testing can be found at Non-Emergency Regulations FAQs on Testing.
Local health jurisdictions (LHJs) may modify these guidelines to account for local conditions or patterns of transmission and may impose requirements in specific settings. Additionally, CDPāH will continue to reassess this guidance and update it accordingly, based on emerging evidence and U.S. Centers for Disease Control and Prevention (CDC) updates.
Previous Infections
For all the testing strategies described below, people who have had a previous infection within the last 30 days and do not have symptoms are not recommended to test.
People who have had a previous infection in the past 31-90 days may be tested with an antigen test. Molecular (NAAT/PCR) tests are not recommended for people who had a previous infection in the last 90 days. For more information, see COVID-19 Testing: What You Need to Know | CDC.ā
Diagnostic Testing for COVID-19
What is diagnostic testing?
Diagnostic testing for COVID-19 is used to diagnose people with a current SARS-CoV-2 infection. SARS-CoV-2 is the virus that causes COVID-19.
Who should have diagnostic testing?
Diagnostic testing should be considered for all people with symptoms of or exposure to COVID-19.
What are the symptoms of COVID-19?
CDC's list of symptoms of COVID-19 includes fever or chills, cough, shortness of breath or difficulty breathing, fatigue, muscle or body aches, headache, new loss of taste or smell, sore throat, congestion or runny nose, nausea or vomiting, and diarrhea. Severe symptoms of COVID-19 include, but are not limited to, trouble breathing, persistent pain or pressure in the chest, new confusion, inability to wake or stay awake, pale, gray, or blue-colored skin, lips, or nail beds (depending on skin tone). A list of symptoms is available at the CDC symptoms page. ā
What types of tests can be used for diagnostic testing?
Diagnostic testing may be performed using either antigen or molecular tests (see details below in the Test Types section).
If a person with symptoms tests negative for COVID-19 with an antigen test, what follow-up testing should be done?
If a person has COVID-19 symptoms and tests negative on an antigen test, they should test again at least a day later at least once after the first test. If a person has a negative result on the second test and is still concerned that they could have COVID-19, they may consider antigen testing again at least another day later after the second test (for a total of 3 tests), OR getting a laboratory-based molecular test (such as NAAT/PCR), and/OR calling their healthcare provider.
Diagnostic Screening Testing for COVID-19
What is diagnostic screening testing?
Diagnostic screening testing is testing of asymptomatic people without known exposure to detect COVID-19 early, stop transmission, and prevent outbreaks.
Who may be considered for diagnostic screening testing?
Diagnostic screening testing is no longer recommended in general community settings as it is less effective at reducing COVID-19's impacts in settings where disease rates are lower, risk of spread is lower, and risk of severe illness is lower. However, individuals may consider routine diagnostic screening testing if they have underlying immunocompromising conditions (e.g., organ transplantation, cancer treatment), due to the greater risks such individuals face if they contract COVID-19. CDPH encourages immunocompromised individuals to discuss their plan with their healthcare providers.ā
What types of tests can be used for diagnostic screening testing?
Antigen or molecular tests can be used and must either: 1) have Emergency Use Authorization by the U.S. Food and Drug Administration; OR 2) be a test operating under the Laboratory Developed Test requirements of the U.S. Centers for Medicare and Medicaid Services.
These tests may be used at different minimum frequencies. See below for details. Additional details on effective testing may be found in CDPH Guidance on the Use of Antigen Tests for Diagnosis of Acute COVID-19 and the CDC's COVID-19 Testing: What You Need to Know.
How frequently should diagnostic screening testing occur?
Molecular testing (PDF) is most effective when turnaround times are short (less than 1 day). If the turnaround time is longer than one day, diagnostic screening testing with PCR or NAAT is a less effective sācreening method. Refer to the CDC's COVID-19 Testing: What You Need to Know for more information.
For additional CDC recommendations on testing, see CDC Overview of Testing for SARS-CoV-2, the virus that causes COVID-19 site.ā
Post-Exposure Testing for COVID-19 Contacts
What is post-exposure testing?
Post-exposure testing for COVID-19 means testing people who are asymptomatic but have been exposed to a confirmed case of COVID-19.
Who should receive post-exposure testing?
Post-exposure testing should be considered when āclose contact" with a case occurs, as defined in the Guidance on Isolation and Quarantine for COVID-19. Post-exposure testing is not recommended if a person was infected with COVID-19 in the last 30 days, unless they develop new symptoms. If new symptoms consistent with COVID-19 occur and an alternative etiology cannot be identified, antigen testing may be considered. Interpretation of positive test results in such people should be made in consultation with infectious disease or infection control experts. For persons infected in the last 31-90 days, post-exposure testing using antigen tests is recommended.
When should post-exposure testing occur?
People who are asymptomatic but have been exposed to a confirmed case of COVID-19 should test 3-5 days after the last exposure date (Day 0), even if asymptomatic. If testing negative before Day 3, retest a day later at least once, during the 3ā5 day window following the exposure.
In addition, people who have been exposed should consider testing as soon as possible to determine infection status and follow all isolation recommendations if testing positive. Knowing one is infected early enables: (a) earlier access to treatment options, if indicated (especially for those who may be at risk for severe illness); and (b) notification of exposed persons (close contacts) who may also benefit by knowing if they are infected.
Any person who develops new symptoms of COVID-19 should be tested right away.
Consult Cal/OSHA COVID-19 Prevention Non-Emergency Regulations for current requirements for employers, and specifically Non-Emergency Regulations FAQ on Testing, for information on testing of workplace close contacts after workplace exposure.
What types of tests can be used for post-exposure testing?
Antigen or molecular tests (including NAAT/PCR) can be used for post-exposure testing.ā
Response Testing
What is response testing?
Response testing is serial testing which can be performed following an exposure or potential outbreak in high risk environments as defined by CDC, such as residential congregate settings or indoor high-density workplaces. The goal of response testing is to identify asymptomatic infections to prevent further spread of COVID-19. When implemented, response testing should be initiated as soon as possible after a person in the setting has been identified as having COVID-19 or when a potential outbreak may be occurring.
For more information about response testing, see Considerations for Testing in High-risk Settings section below.
After a Positive COVID-19 Test
What should people do after testing positive for COVID-19?
People who have a positive COVID-19 test should follow the CDPH Guidance on Isolation and Quarantine for COVID-19.
Medications to treat COVID-19 are free, widely available, and effective at stopping COVID-19 illness from making you seriously ill. Everyone 12 years of age and older who has symptoms and tests positive for COVID-19 should ask a medical provider about treatment. Visit the COVID-19 treatments site for more information.
Some people who get COVID-19 may continue to have symptoms for weeks or months. Learn what resources are available if you are not recovering from COVID-19 at the Post-COVID-19 Conditions (Long COVID) site and the CDPH: Post-COVID Conditions website.ā
Considerations for Testing in High-risk Settings
What is a high-risk setting?
High-risk settings include residential congregate facilities with high risk for transmission and large-scale outbreaks, and/or facilities where persons at higher risk of severe disease are more likely to be present. These include settings where people may have little control over their contacts and interactions that can include frequent exposure to staff and others. In many of these settings, persons are at high risk of severe COVID-19 disease due to underlying health conditions, advanced age, or both.
Regular testing (when appropriately followed by isolation of individuals who test positive), can contribute to reduction of transmission risk in these high-risk settings.
What facilities are considered high-risk settings?
High-risk settings includes the following:
Healthcare settings (which include skilled nursing facilities) should follow testing guidance included in CDC's healthcare infection control guidance, and recommendations for post-exposure and return-to-work testing of healthcare personnel as set forth in AFL 21-08.9. Healthcare personnel working in settings not covered by AFL 21-08.9 may follow the guidance outlined in AFL 21-08.9.
Intake and Admission Testing
Skilled nursing facilities should provide admission testing in accordance with CDC's healthcare infection control guidance. Other non-healthcare residential congregate facilities may consider screening testing of new residents at the time of intake or upon admission to reduce the risk of COVID-19 transmission in these settings.
Response testing
Response testing is serial testing performed following an exposure or potential outbreak that has occurred in a high-risk environment. ā
- Who should be tested during response testing?
- When recommended, response testing should include all individuals within an exposure risk cohort, regardless of vaccination status.
- What tests can be used for response testing?
- Either antigen or molecular tests can be used for response testing. Antigen tests are preferred for faster turn-around time.
- How frequently should response testing occur?
- āWhen implemented, the recommended minimum frequency of response testing is at least once weekly for molecular testing or twice per week for antigen testing.
- More frequent testing may be useful when many in the community may have COVID-19 and be infectious to others and when the circulating variant has a short incubation period. Molecular testing (PDF) as a response testing tool is most effective when turnaround times are short (less than 1 day). If the turnaround time is longer than one day, response testing with molecular tests is not an effective method.
- How long should response testing continue?
- āResponse testing should be performed initially, and then serial testing of those who tested negative on the prior round of testing should continue until no new cases are identified in sequential rounds of testing over a 14-day period. Facilities should work with their LHJ on outbreak management.
- āResponse testing for outbreaks in workplaces
- Facilities must follow Cal/OSHA requirements for outbreak management, or LHJ requirements if they exceed Cal/OSHA standards.
Skilled nursing facilities and LHJs may refer to CDC infection control for guidance on situations where a contact-tracing approach may be used to guide response testing.
Diagnostic screening testing
While diagnostic screening testing is no longer recommended in general community settings, it may still be considered in high-risk settings where transmission risk is high, the population served is at high risk of severe outcomes from COVID-19, or where there is limited access to healthcare.
Screening testing may be considered for individuals at intake and admission to residential congregate facilities. In certain circumstances, such as when many in the surroundināāg community may have COVID-19 and be infectious to others, or when there are outbreaks with high rates of post-exposure testing refusals, additional screening testing can be used as an enhanced prevention strategy. If implemented, it should include all persons, regardless of vaccination status, given recent variants and subvariants with significant immune evasion.
High-risk settings should also consider maintaining testing capacity to perform diagnostic screening testing during outbreaks, and for easier implementation if testing becomes required again at a future date. High risk settings may also consider various screening testing strategies (such as point in time testing, sampling testing, etc.) and testing based on how many in the surrounding community may have COVID-19 and may be infectious to others. For more information related to vulnerable populations visit the CDC People with Certain Medical Conditions page.ā
Testing and Traveling
Should people who are traveling have pre-travel and/or post-travel testing?
See CDC recommendations for domestic and international travel.
Test Types
What types of tests are there?
For more detailed information on types of tests and additional details, visit the U.S. Food and Drug Administration (FDA) diagnostic tests site.
Molecular tests amplify and then detect specific fragments of viral RNA. Depending on the test, different sequences of RNA may be targeted and amplified. Examples of this method include polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP), and Nucleic Acid Amplification Test (NAAT). Point-of-care (POC) molecular tests can produce rapid results in less than 30 minutes but may have lower sensitivity (might not detect all active infections) compared with laboratory-based PCR tests.
Antigen tests identify viral nucleocapsid protein fragments. They are typically performed at POC or at home and produce results in approximately 10-30 minutes.
Antigen tests have a slightly lower sensitivity (may not detect all active infections), but similar specificity (likelihood of a false positive test result for those not infected with SARS CoV-2) for detecting SARS-CoV-2 compared to molecular tests.
Antigen test samples must be collected as directed in instructions for the specific test (e.g., a sample from the nose is required for a test that has been approved for nasal swabs).
The U.S. Food and Drug Administration (FDA) maintains a list of diagnostic tests for COVID-19 that have been granted Emergency Use Authorization (EUA). No test is 100% accurate and if you have questions about your test results, talk to a healthcare provider. While waiting talk to a provider, follow CDPH isolation precautions. ā
Where can I find free COVID-19 tests?
For up-to-date information on testing sites, visit the CDC No-Cost Testing Locator. Information about getting at-home tests free through medical insurance and additional testing site resources are available at How to Get Tested.
What factors can impact the accuracy of COVID-19 tests?
Multiple factors can affect the accuracy of a COVID-19 test result. Because no test is perfect, contact your medical provider with any questions about your test results. While waiting to contact your provider, take steps to prevent transmitting COVID-19 to others in the CDPH Guidance on Isolation and Quarantine for the General Public .
All COVID-19 tests work by detecting the virus in your body. Tests will be able to diagnose a current infection more accurately if you have more virus present. The amount of virus that is present in the testing site (e.g., nasal cavity) at a given time is referred to as a viral load. Additionally, a person's individual immune response and their personal health characteristics can impact the timing and course of their infection, which will influence the level of viral load at any given point in time. In general, after exposure and infection, the amount of detectable virus in the body remains low for the first few days, then rises exponentially and decreases gradually.
Different tests also have different performance characteristics. This is measured as sensitivity and specificity:
Antigen tests and molecular tests have different limits of detection (levels of virus that can be detected) which impact their sensitivity. Each lab's tests have their own sensitivity and specificity levels.
Appropriate sample collection is important for the best āāresults. Factors including collection technique and sealing of specimen, storage temperature, transportation, sample handling, and duration of time between sample collection and testing can impact sample integrity.
References
Takahashi K, Ishikane M, Ujiie M, et al. Duration of Infectious Virus Shedding by SARS-CoV-2 Omicron VariantāInfected Vaccinees Emerg Infect Dis. 2022;28(5):998-1001.
Cosimi LA, Kelly C, Esposito S, et al. Evaluation of the role of home rapid antigen testing to determine isolation period after infection with SARS-CoV-2. medRxiv 2022.03.03.22271766. āāā
Originally Published on June 7, 2021