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Updates as of September 15, 2022:

• Updated guidance on using antigen testing to end isolation.
• Updated references to applicable guidance for Isolation and Quarantine and Events.
• Updated language to replace "fully vaccinated" with "completed primary series" to bring outdated terminology up to date.

Background

Testing for COVID-19 identifies infected people. This is important to help guide infected people to appropriate treatment, as well as to reduce forward transmission by isolation of infected people and notification of close contacts of their exposure. Testing is one layer in a multi-layered approach to COVID-19 harm reduction, in addition to other key measures such as vaccination, mask wearing, improved ventilation, respiratory and hand hygiene. 

See CDPH guidance and State Public Health Officer Orders for more specific testing requirements in certain settings. In the workplace, employers are subject to the Cal/OSHA COVID-19 Prevention Emergency Temporary Standards (ETS) or in some workplaces the Cal/OSHA Aerosol Transmissible Diseases (ATD) Standard (PDF), and should consult those regulations for additional applicable requirements. Additional information about how CDPH testing affects ETS-covered workplaces may be found in Cal/OSHA FAQs.

Testing Guidance

Local health jurisdictions (LHJs) may modify these guidelines to account for local conditions or patterns of transmission and may impose stricter requirements than those applicable statewide. Additionally, the California Department of Public Health (CDPH) will continue to reassess this guidance and adjust them accordingly based on emerging evidence and U.S. Centers for Disease Control and Prevention (CDC) updates.

Diagnostic Testing for COVID-19

What is diagnostic testing?

Diagnostic testing for COVID-19 is used to diagnose people with SARS-CoV-2 infection. SARS-CoV-2 is the virus that causes 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). Symptom lists are available at the CDC symptoms and testing page. 

Who should have diagnostic testing?

Diagnostic testing should be considered for all people with symptoms of or exposure to COVID-19.

What types of tests can be used for diagnostic testing?

Diagnostic testing may be performed using either antigen testing or molecular testing (see details on antigen and molecular testing below in the Tests section).

If symptomatic individuals test negative for COVID-19 with an antigen test, what follow-up testing should be done?

People at high risk for hospitalization or death from COVID-19* benefit from early treatment and should have an immediate PCR (or other molecular) test and repeat an antigen test (at-home tests are acceptable) in 24 hours if the PCR result has not returned. Sometimes people with COVID-19 have a negative antigen test in the first few days of symptoms. PCR (or other molecular tests) may detect the virus earlier than an antigen test.

For low-risk people, repeat an antigen test (at-home tests are acceptable) in 24-48 hours. Individuals may consider repeat testing every 24-48 hours for several days until a positive test or until symptoms improve.

*List of conditions that increase the risk of hospitalization or death from COVID-19

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 should have diagnostic screening testing?

Diagnostic screening testing is no longer recommended in general community settings. Diagnostic screening testing may still be considered in high-risk settings. However, if implemented it should include all persons, regardless of vaccination status, given recent variants and subvariants with significant immune evasion.

Who must have diagnostic screening testing?

Diagnostic screening testing recommendations vary, depending on whether the setting is high-risk, including healthcare settings.

For testing recommendations in non-high-risk settings, please refer to the CDC COVID-19 Testing Guidance and CDPH COVID Testing in California.

High-risk settings, unless specifically required, may consider maintaining testing capacity to perform diagnostic screening testing during outbreaks, and in the event it is required again at a future date. Settings may also still consider various screening testing strategies (point in time testing, sampling testing, etc.) and testing based on concerning levels of local transmission.

Workers may also 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.

Tracking results

Employers who conduct workplace diagnostic screening testing should have a plan in place for tracking test results, conducting workplace contact tracing, and reporting positive test results to local health departments. For more information on tracking and reporting in the workplace, please refer to the Workplace Outbreak Employer Guidance (ca.gov).

Additionally, please refer to Cal/OSHA ETS for more detailed workplace guidance, especially as described in Sections 3205(c)(1), 3205(c)(2), and 3205(c)(3).

In the case of multiple COVID-19 cases, please refer to Sections 3205.1(b) and 3205.1(c). In the case of 20 or more employee cases, please refer to Section 3205.2(b). 

Technology platforms are available that can facilitate reporting for employers. Employers should also consult CDPH's AB 685 COVID-19 Workplace Outbreak Reporting Requirements, Employer Questions about AB 685,  CDC guidance on workplace screening testing and Responding to COVID-19 in the Workplace Guidance for Employers for additional information.

Testing can complement other COVID-19 prevention measures, such as vaccination, mask wearing, improved ventilation, respiratory and hand hygiene.

What types of tests can be used for diagnostic screening testing?

Antigen or molecular tests can be used and must either have Emergency Use Authorization by the U.S. Food and Drug Administration or 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, please see below for details. More 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?

Settings that should be considered for screening testing include facilities and situations where transmission risk is high and the population served is at high risk of severe outcomes from COVID-19 or there is limited access to healthcare.  Serial screening testing 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. Because of this, CDC and CDPH do not recommend serial screening testing in most lower risk settings.

Diagnostic screening testing frequency: The current recommended minimum COVID-19 diagnostic screening testing frequency is at least once weekly for molecular testing and twice weekly for antigen testing.

For more information on testing in schools, see CDPH Preliminary Testing Framework for K–12 Schools for the 2022–2023 School Year (PDF) and 2022-2023 K-12 Schools to Support Safe In-Person Learning.

Molecular testing (PDF) is most effective when turnaround times are short (<2 days). If the turnaround time is longer than 1 day, diagnostic screening testing with PCR or NAAT is a less effective screening method. Please refer to the CDC's COVID-19 Testing: What You Need to Know.

For additional CDC recommendations on testing, see CDC Overview of Testing for SARS-CoV-2, the virus that causes COVID-19 site

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 and when should it occur?

• All people, regardless of vaccination status, who have shared the same indoor airspace for a cumulative total of 15 minutes or more over a 24-hour period during an infected person's infectious period [3] should consider testing immediately upon exposure notification and 3-5 days after their exposure date (day 0), even if they are asymptomatic.
• Exposed people who were infected within the prior 90 days do not need to be tested unless symptoms develop. However, such people may consider testing if exposed 30-90 days after previous infection since people exposed to new variants may become re-infected in less than 90 days.
• Any person who develops new symptoms of COVID-19 should isolate and be tested right away. For more relevant guidance, please refer to the latest Isolation and Quarantine for COVID-19 Guidance.
• Consult Cal/OSHA COVID-19 Prevention Emergency Temporary Standard and specifically, the ETS Testing Section and ETS FAQ on Testing for current requirements for employers to offer testing of workplace close contacts after workplace exposure.

What types of tests can be used for post-exposure testing?

Molecular, including PCR, or antigen tests can be used for post-exposure testing.

Response Testing

What is response testing?

Response testing is serial testing performed following an exposure that has occurred in high-risk residential congregate settings or high-risk/high-density workplaces. The goal of response testing is to identify asymptomatic infections in people in high-risk settings and/or during outbreaks to prevent further spread of COVID-19. Response testing should be initiated as soon as possible after a person in a high-risk setting has been identified as having COVID-19.

Skilled nursing facilities and LHJs may refer to AFL 22-13 for Skilled Nursing Facilities for guidance on situations where a contact-tracing approach may be used to guide response testing and quarantine.

Who should be tested during response testing?

Response testing should occur for all people (residents and staff, regardless of vaccination status) in the facility as soon as possible after at least one person (resident or staff) with COVID-19 is identified in a high-risk setting.

What tests can be used for response testing?

Either antigen or molecular tests can be used for response testing. Antigen tests are preferred for fastest turn-around time.

Response testing frequency

The recommended minimum response test frequency is at least once weekly.  More frequent testing may be useful when community levels of transmission increase, in communities with low vaccination rates, 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 (<2 days). If the turnaround time is longer than 2 days, response testing with molecular tests is not an effective method.

How long should response testing occur?

Response testing should be performed on all residents and staff initially, and then serial testing of those who tested negative on the prior round of testing should occur 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.

Response testing for outbreaks in workplaces

Facilities must follow Cal/OSHA standards for outbreak management, or LHJ requirements if they exceed Cal/OSHA standards. All people who are exposed [1] should follow Guidance on Isolation and Quarantine for COVID-19 (ca.gov).

Pre-entry / Pre-admission / Pre-competition/ Pre-travel testing for COVID-19

What is Pre-entry Testing?

Pre-entry testing is testing performed prior to someone entering an event, competition, congregate setting, or other venue or business and is intended to reduce the risk of COVID-19 transmission in these settings. Symptomatic people and people with positive COVID-19 test results should not be allowed to enter.

Who must receive Pre-entry Testing?

Refer to CDPH Guidance for Mega Events for more information on pre-entry testing for large indoor events.

Who should receive Pre-entry Testing?

In addition to settings where pre-entry testing may be required, it should be considered for those attending large indoor social or mass gatherings (such as large private events, live performance events, sporting events, theme parks, etc.) especially if high-risk individuals will be present, while participating in high-risk sport competitions, or other events in crowded or poorly ventilated settings.   

What types of tests can be used for pre-entry testing and when should they be performed?

CDPH recommends a point of care test (antigen or molecular) within 24 hours of entry for asymptomatic people. Results should be available before event entry.

What can be used as proof of a negative pre-entry test in settings where pre-entry testing is required?

For settings that require pre-entry negative tests, facilities and venues should not use self-attestation. The following are additional strategies that may be used as acceptable for proof of a negative COVID-19 test result:

• A printed document from the test provider or laboratory; OR
• An electronic test result displayed on a phone or other device from the test provider or laboratory.

• The information should include person's name, type of test performed, and negative test result. OR
  
• A supervised antigen test where test process and result are observed by staff.

For more guidance on how to provide proof of testing and vaccination, please refer to Vaccine Records Guideline & Standards.

Testing and Traveling

Should people who are traveling have pre-travel testing?

CDC recommends that domestic travelers, regardless of vaccination status, consider getting tested for current infection with a viral test as close to the time of departure as possible (no more than 3 days before travel).

Travelers entering the US by air from international locations are no longer required to test prior to US entry. For more information on testing and other protective measures to take while traveling, please refer to CDC Travel During COVID-19.

Testing and Events

Should testing occur after the event, and if so, when?

Since there is a possibility of exposure to people infected with COVID-19 in gatherings and congregate situations, testing 3-5 days after the event is recommended even if no symptoms develop.

All people who develop symptoms should test immediately. If a person with symptoms of COVID-19 initially tests negative on an antigen test, the test should be repeated in 24-48 hours.

Symptomatic people may consider repeat testing every 24-48 hours for several days after symptom onset until there is a positive test result or until symptoms improve. Low amounts of virus early in infection can sometimes be missed by antigen tests, and an antigen test can be positive when repeated within several days.

Should symptomatic people attend events if they have negative pre-entry test results?

People experiencing COVID-19-like symptoms (PDF) should be tested and should not attend events or gatherings or visit congregate settings even if they are antigen test negative during the first few days of symptoms; this is recommended in general to reduce spread of infectious diseases. Such persons should retest with an antigen or molecular test 24-48 hours after the initial negative antigen test.

Testing after a diagnosis of COVID-19

• People who have an initial positive COVID-19 test should isolate for at least 5 days (the first day of symptoms or the date of a positive test in someone who never develops symptoms is Day 0). For the most up to date information on when to start and end isolation as well as other measures to take when in isolation, please refer to CDPH Isolation and Quarantine for COVID-19 Guidance for the General Public.
  
• People who had a positive COVID-19 test in the past 90 days and are currently asymptomatic do not need to be retested as part of a diagnostic screening testing program; screening testing may be considered again 30-90 days after previous infection since people exposed to new variants may become re-infected in less than 90 days.
• People who had a positive COVID-19 test in the past 90 days and are exposed to COVID-19 do not need to be tested unless symptoms develop. However, such people may consider testing if exposed 30-90 days after previous infection since people exposed to new variants may become re-infected in less than 90 days.
• Testing with an antigen test within 30 days of a prior infection may be considered for people who develop new symptoms consistent with COVID-19, IF an alternative etiology cannot be identified. Interpretation of positive test results should be in consultation with infectious disease or infection control experts.

Prolonged antigen test positivity after COVID-19 infection

CDPH has received reports of infected people with antigen test positivity >10 days.

There are limited data available to inform recommendations for such people but a recent viral culture study with the Omicron variant [2] did not identify infectious virus >10 days after symptom onset.

A second recent study [3] during the Omicron BA.1 surge found that antigen tests were suboptimal at predicting the ability to culture virus on day 6, which suggests that negative antigen tests are predictive of a negative culture, but positive antigen tests may be detecting non-culturable virus.

Therefore, CDPH recommends that most infected persons may stop testing and discontinue isolation after day 10 even if an antigen test is still positive, as long as symptoms are improving, and fever has been resolved for 24 hours without the use of fever-reducing medication. However, it is possible that some infected people remain infectious >10 days. Thus, persons who continue to test antigen positive on or after day 10 should consider continued masking and refraining from contact with people at high-risk for severe COVID-19 disease until their antigen test is negative.

Tests

What types of tests are there?

 Molecular tests:  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).

The real-time reverse transcriptase polymerase chain reaction (PCR) is the most commonly used molecular test and the most sensitive test for COVID-19. PCR is typically performed in a laboratory and results typically take one to three days.

Point-of-care (POC) molecular tests are also available and can produce results in 15 minutes but may have lower sensitivity (might not detect all active infections) compared with laboratory-based PCR tests.

 Antigen 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 negative test for those not infected with SARS CoV-2) for detecting SARS-CoV-2 compared to PCR 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 granted Emergency Use Authorization (EUA). No test is 100% accurate and test performance can vary depending on test and patient factors, as well as current community transmission rates and pre-test probability in the person being tested. These recommendations for antigen testing and frequency are subject to change based on overall test positivity, local case rates and levels of transmission.

Where can I find free COVID-19 PCR tests?

For updated information on testing sites and getting at-home tests free through medical insurance, visit Find a testing site (ca.gov)

What factors can impact the results of COVID-19 tests?

• Viral Load: the amount of virus that is present in the testing site (e.g., nasal cavity) at a given time. 
• Sensitivity: ability of a test to turn positive when a person is in fact infected with SARS CoV-2.
• Specificity: ability of a test to be negative when a person is not infected with SARS CoV-2.
• Stage of Infection: Sensitivity is also highly dependent on the stage of the infection. In general, after exposure and infection the amount of detectable virus in the body remains low for the first few days of infection, then rises exponentially and then decreases gradually over a period of time.
• Immune response of the infected person: A person's individual immune response and their personal health characteristics can impact the time course of their infection, which will influence the level of viral load at any time point.
• Different laboratories: Each lab's tests have their own sensitivity and specificity levels. Labs with a higher level of sensitivity can detect lower viral loads of COVID-19 that might not be detected by a test with a lower sensitivity level.
• Different tests: Antigen tests and molecular tests have different limit of detection to detect virus thus impacting their sensitivities.
• Sample collection and handling: Effective sample collection is dependent on different factors that can impact sample integrity including collection technique and sealing of specimen, storage temperature, transportation, sample handling, and duration of time between sample collection and testing. 

References

[1] Someone sharing the same indoor airspace, e.g., home, clinic waiting room, airplane etc., for a cumulative total of 15 minutes or more over a 24-hour period (for example, three individual 5-minute exposures for a total of 15 minutes) during an infected person's (laboratory-confirmed or a clinical diagnosis) infectious period.

[2] Takahashi K, Ishikane M, Ujiie M, et al. Duration of Infectious Virus Shedding by SARS-CoV-2 Omicron Variant–Infected Vaccinees. Emerg Infect Dis. 2022;28(5):998-1001.

[3] 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. 

Originally Published on June 7, 2021