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Background
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.
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), facilities, and other organizations (such as high-risk congregate settings) may modify these guidelines to account for local conditions, populations served, or patterns of transmission and may implement more protective requirementsāā in specific settings. Additionally, CDPāH will continue to reassess this guidance and update the guidelines 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 CDC COVID-19 Testing: What You Need to Know.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 is recommended for all people with new symptoms of COVID-19.
- Diagnostic testing is recommended for exposed people without symptoms who are at higher-risk of severe COVID-19 infection and may benefit from treatment if infected or who have contact with people at higher-risk for severe infection.
What are the symptoms of COVID-19?
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 (note that antigen
tests in infected people may not be positive right away even if symptoms are
present). 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). The person is
also highly recommended to call their healthcare provider who may consider testing
for other viral infections or illnesses depending on the severity of their
symptoms and/or risk of serious disease.ā
Diagnostic Screening Testing for COVID-19
What is diagnostic screening testing?
Diagnostic screening testing is testing of people without symptoms or known exposure to detect COVID-19 early, stop transmission, and prevent outbreaks or control 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)āā 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 (EUA) by the U.S. Food and Drug Administration (FDA); 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 the question and answer below for details. Additional details on effective testing may be found in the CDC's COVID-19 Testing: What You Need to Know.āā
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
If performed, when should post-exposure testing occur?
Anyone with new symptoms of COVID-19 should test right away (see Diagnostic Testing above).
People who have been exposed to a confirmed case of COVID-19 and do not have COVID-19 symptoms are only recommended to test if they are at higher risk of severe disease and would benefit from treatment OR if they have contact with people who are at higher risk for severe COVID-19 infection. In these situations, they should consider testing within 5 days after the last exposure date (Day 0) and prior to contact with highāāer risk people.
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.
Consult Cal/OSHA COVID-19 Prevention Non-Emergency Regulations for current requirements for employers, and specifically Non-Emergency Regulations FAQs on Testing, for information on testing of workplace close contacts after workplace exposure. During workplace outbreaks, additional testing is required.
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
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 COVID-19 Isolation Guidance.
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 treatment site for more information. Medications to treat COVID-19 are widely available, and effective at reducing the severity of COVID-19 illness. Most insurance plans cover COVID-19 treatment. Visit the CDPH treatment pageā or call the 1-833-422-4255ā to locate medications at no cost if you do not have a healthcare provider.
āSome people who get COVID-19 may continue to have symptoms for weeks or months. Learn what resources are available on the CDPH: Post-COVID Conditions websiteā.
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.
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.
Response Testing
What is response testing?
Response testing is serial testing which can be performed following an āāexposure or potential outbreak in high-risk environments. Response testing has been used to identify asymptomatic infections to prevent further spread of COVID-19. When implemented, response testing should be initiated as soon as possible when a potential outbreak may be occurring.
For more information:
- Facilities and workplaces must follow Cal/OSHA requirements for outbreak management, or LHJ requirements if they exceed Cal/OSHA standards.
- Facilities should work with their LHJ on outbreak management.
- Skilled nursing facilities and LHJs may refer to CDC COVID-19 infection control for guidance on situations where a contact-tracing approach may be used to guide response testing.
Intake and Admission Testing
Skilled nursing facilities should provide adāāāāmission 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, especially during period of increased COVID-19 transmission.
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.
- In certain circumstances, such as when many in the surrounding 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.
- āIf implemented, screening testing should include all persons, regardless of vaccination status, given potential variants and subvariants with significant immune evasion.
High-risk settings should also consider maintaining testing capacity to perforām 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 ātraāvel.
Test Types
What types of tests are there?
For more detailed information on types of tests and additional detailsā, visit the 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. āāAntigen 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 FDA maintains a list of diagnostic tests for COVID-19 that have been granted EUA. No test is 100% accurate. A healthcare provider should be consulted for any quesitons regarding test results. Those waiting talk to a healthcare provider should follow CDPH isolation precautions. ā
Where can I find free COVID-19 tests?
Most insurance plans cover
COVID-19 home tests. Testing locations can be found at Find
a testing site or No-Cost
COVID-19 Testing. Information
about getting free at-home tests through medical insurance and additional testing
site resources is 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 a healthcare provider with any questions.
All COVID-19 tests work by detecting the virus in the body. 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.ā Tests will be able to diagnose a current infection more accurately if multiple viruses are present.āā Additionally, a person's individual immune response and their personal health characteristics can impact the tiāming 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