The following was written by Sharon Bogan for Public Health Insider, the official blog for Public Health — Seattle & King County:

With the current Omicron surge, demand for testing continues to be extremely high. Many people are seeking tests after experiencing symptoms of COVID-19, or being exposed to someone who has tested positive. Those who have tested positive may also be looking to test before returning to their activities. We’re all doing what we can to try and limit transmission and yet, it can be confusing to know what test to use in each circumstance and to know what to do if you can’t get a test.

Public Health has been working to procure rapid in-home tests through as many avenues as possible. Until there is more supply, here are some tips on testing in this moment:

WHAT IS THE DIFFERENCE BETWEEN RAPID ANTIGEN (OVER-THE-COUNTER, AT-HOME) TESTS AND PCR TESTS?

• Antigen tests, also called rapid or over-the-counter tests, are usually self-tests done at home. These test kits are ones with names like BinaxNOW, Flowflex, QuickVue, iHealth, and many others. These tests detect specific proteins on the surface of the virus. Rapid antigen test results can take as little as 15 minutes to complete. These tests are an effective way to test for COVID-19 in most situations, especially when results are needed quickly.

• A positive rapid test is a good indicator that someone has COVID-19 and can spread it to others. However, a negative test is not like getting a permission slip to stop taking the actions that prevent COVID-19. That’s because rapid tests can be negative in the first few days of the infection when they can’t yet detect antigens that signal a case of COVID-19. If you have symptoms or suspect you have COVID-19, it’s important to still take precautions even if you have a negative test, especially if you will be around people at high risk for severe illness.

• PCR tests are the tests that are used at most COVID-19 testing sites and health care providers. These can detect the presence of the virus in earlier stages of infection than antigen tests but take longer for results to come back. With PCR tests, sometimes people continue to test positive for weeks after they have recovered and can no longer spread the virus. That’s because PCR tests can detect genetic material from the virus that causes COVID-19 in the body even after the infection is over. This is why a PCR test is not a good test to use if you are positive and want to see if you should leave isolation. Results usually come back in a couple days.

Learn more about the differences between tests.

WHAT TEST SHOULD I USE?

There are a few scenarios when someone may be seeking testing:

1. Testing if exposed

If you are up to date with your vaccinations (including a booster shot for people 18 and older) and you have been exposed to someone with COVID-19, you can use either a rapid antigen test or a PCR test (at least five days after your last contact).

For example: You are fully vaccinated and boosted and your co-worker tested positive. You all wear masks while working, but you had lunch together in a small office when your masks were off. You can either schedule a PCR test or use a rapid test. Wait five days after your exposure before you test if you don’t have symptoms. If you test too early, you may not have enough virus in your system to be detected by the test. If you start to have symptoms, you can test right away — it’s best to assume you have COVID-19, isolate and stay away from others.

If you aren’t up to date on your vaccinations:

Anyone in the following groups who is exposed should quarantine (stay in your home):

• Unvaccinated people or adults who haven’t had a booster shot yet

• People under 18 years who haven’t completed their initial vaccinations (2 shots of Pfizer)

Quarantine away from others for at least five days and wear a good quality/well-fitting mask when around others at home. Then, get tested with either a rapid antigen or PCR test.

2. Testing if you have symptoms

Whether you have been exposed to someone with COVID-19 or not, if you have symptoms, even mild ones like a headache or mild sore throat, you should isolate away from others right away and schedule a PCR test or use a rapid test if you have one. Continue to stay home until you know the results. Wear a well-fitted mask around others in your home. If you test negative, repeat testing in two days if possible.

3. Testing after having COVID (leaving isolation)

If you are testing to end isolation after you’ve previously tested positive for COVID-19, use a rapid antigen test on day five (or after) if it is available to you. You want to be sure you are without fever the past 24 hours and that symptoms are mostly gone before returning to work or activities.

For example: You tested positive for COVID on Saturday. You had a headache. It’s Friday, and you feel better and have not had a fever for 24 hours without taking fever-reducing medications (like Tylenol). (Sunday is considered Day 1 and you can return after five full days.)

If you don’t have a rapid test, you can return to your activities with some precautions (see below). If you are able to take a rapid test, and it comes back positive, you are likely still contagious and should continue to isolate for five more days.

4. Testing to gather more safely

If you want to gather more safely with family or close friends, the best option is to use a rapid antigen test as close to the time of the event as possible. Remember that rapid tests can be negative in the first few days of infection and don’t guarantee that you aren’t infected, so continue to take precautions, especially around higher risk people.

WHAT IF I CAN’T GET THE TEST I NEED?

Tests are hard to come by right now, so here’s what to do:

• If you have symptoms, it’s best to assume that you have COVID-19. Isolate away from others for at least five days. As we say, “when in doubt, sit it out.”

• If you think you have been exposed with someone with COVID-19 but can’t get a rapid test or a PCR test appointment, pay attention to any possible symptoms. Be extra cautious and limit being around other people to the extent possible. When you are at work or school, wear the highest quality, best-fitting mask you can. If you aren’t up to date on your vaccinations, you need to quarantine away from others for at least five days.

• If you are isolating, and can’t get a rapid test, you can return to your activities at the end of five days if your symptoms are improving and you haven’t had a fever for 24 hours (without taking Tylenol or other fever-reducing medications), and you feel OK. Wear the best quality mask you can for another five days. You should also avoid contact with people at high risk for severe COVID-19, such as older adults and people who are immune compromised.

Additional guidance at CDC’s Isolation and Quarantine website.

DON’T GO TO THE ER FOR TESTING

Please do not go to the emergency departments or urgent care clinics for COVID-19 testing. They are overloaded caring for ill patients and can’t provide testing for people who don’t need emergency care.

MORE TESTING RESOURCES

King County purchased 700,000 rapid tests directly from manufacturers and the first 100,000 arrived this week. We are distributing them to some of the highest risk settings such as long-term care facilities, Emergency Medical Services (EMS), correctional facilities, and other high-risk congregate settings, followed by community organizations in areas of greatest need including shelters and senior centers. At this point, we still do not have enough tests to distribute to the general public. We know that is a big limitation and hope that with more testing resources from federal and state partners, availability will begin to increase.

-For more information on testing and a list of free testing locations in King County visit Public Health’s testing page.

-For information on how to do a self-test, including videos in multiple languages, visit Public Health’s self-testing page.