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COVID-19 Information: Santa Clara County and Bay Area, California

Trustworthy information about COVID-19

Who Should Get Tested?

Should you get tested if you think you've come into contact with someone who has COVID-19, or who you suspect has it? 

  • For people generally in good health, use the CDC's online When to Test calculator.
  • For people who may be medically vulnerable, or are in a community that experiences less-than-equitable health care (immigrants, refugees, low-income, Latinx or Black or some Asian communities), use the CDC's more detailed online calculator.
  • To calculate for yourself, read on for the factors to consider.

In general, the current guidelines are that everyone - regardless of vaccination - should get tested if:

  1. they have symptoms of COVID-19, or have been exposed to someone who has tested positive for COVID within the last 5 days;
  2. their work requires that they be tested on a regular basis;
  3. travelling distances (that is, immediately before international travel, domestic air travel, or using public transit to take a trip that is longer than a short trip;
  4. while not required, it is a good idea to test just before visiting vulnerable relatives or friends (skip the visit if test positive).

When to get tested can be a tricky question. Testing too early, before an infection takes hold, can give a false negative test, and could end up spreading the disease. Earlier versions of  SARS-CoV-2 took longer for symptoms to appear, and remained contagious longer, than the omicron variant. Currently the CDC asserts that "transmission of COVID-19 often occurs one to two days before the onset of symptoms and during the two to three days after." But since many cases are asymptomatic, it may be wise to test 2-4 days after coming into contact with a person known or suspect to be infected with COVID.

There may be separate timelines required in workplace settings for testing and quarantining - the CDC's When to Test calculator for organizations, and/or Department of Industrial Relations provide guidance in those circumstances.

If someone tests positive for COVID-19, what to do next depends on vaccination status and how severe the symptoms may be. See this page for current guidelines.

What Test to Use

At present there are more than one test used to find SARS-CoV-2 infections. Two types, PCR tests and antigen tests, are used to discover if someone currently has a COVID infection, so these are most relevant to us as individuals. These use either a nasal swab or saliva to test. (NOTE: be sure to follow the instructions on the specific test kit on where to swab.)

PCR (polymerase chain reaction) tests look for SARS-CoV-2 genetic material. Processing needs to take place in a laboratory, and takes at least 12 hours - usually much longer - to get results. (Which means that, in theory, immediately after testing people should isolate themselves until they know their test results to be absolutely certain that they're not currently infected.) 

When done correctly PCR tests are remarkably accurate at detecting whether SARS-CoV-2 viruses are present - that is, if that person could infect someone else. They can also identify which variant of SARS-CoV-2 is causing the infection, and that is how mutations of this virus are tracked across populations.

At present, PCR tests are offered by health organizations at no extra cost to the individual. For where to get a PCR test in Santa Clara County, see:

Antigen tests (also called rapid tests, lateral flow tests, or home tests) look for the presence of substances that trigger our bodies to produce antibodies. That is, they look for by-products of  COVID infection, not the virus itself. These tests indicate if someone is fighting off a COVID infection, but cannot tell us just how infectious someone might be, or which version of the virus they have. They can be less accurate than PCR tests, especially when too close to the initial infection, or some days after systems peak.

However, they are much faster (around 15 minutes instead of days), and testing can be done anywhere, making these much more convenient. They can be sold over the counter in drugstores or online.

 Funding for free at-home antigen tests from the U.S. government expires in the first week of September 2022.

Health insurance plans may offer free at-home tests, or provide a rebate for purchased test kits -- check with your healthcare plan benefits to find out details.

Because so many people have no symptoms with this disease, the only way to be certain that someone had COVIDin the past is to look for antibodies. Several different trial versions of antibody tests are being used and tested; since these all involve testing for various substances in the blood, these are also referred to as serologic tests. These can be useful to identify past exposure, or to confirm a COVID diagnosis, but cannot answer the question "am I infectious now?". 

Contact Tracing

When a PCR test is positive, you might hear from a contact tracer.

A contract tracer should only ask questions about your COVID-19 symptoms or status, and about the people you may have had contact in a specific period of time.

Contact tracing in-person is a labor-intensive process, and our memories can be fallible. To help automate that process while at the same time protecting our privacy, a new phone app is available in California. For more details, see:


Legitimate contact tracers will never ask you for a Social Security number or about immigration status, for any health insurance or financial information. If you are asked any of those questions, the call is a scam. Please do not give out those details, and make a complaint to the CA State Attorney General.

The text on this page is copyright PlaneTree Health Library, licensed under Creative Commons CC BY-NC-SA 4.0. Linked contents are the responsibility of their creators or copyright holders.