More than two years into the COVID-19 pandemic, it's likely that most of us have been exposed to the virus at least once through close contact.

Being in close contact with someone who has COVID-19—or who later tests positive for COVID-19—is a key indicator that you should test yourself for the virus. By Centers for Disease Control and Prevention (CDC) standards, "close contact" requires two things:

"To meet the definition of 'close contact' you generally need to have spent at least 15 minutes of time in close proximity while the other person was ill or in the two days prior to them becoming ill," Sujit Suchindran, MD assistant professor in the division of infectious diseases at the Emory University School of Medicine, told Health.

But exactly how long should you wait after COVID-19 exposure to test for the virus? Here's what experts suggest, based on the current best practices for testing.

The best time to test—and to ensure that you're going to get an accurate result—is around five days after you've been exposed to the virus, or when you first start experiencing symptoms, explained Dr. Suchindran.

"If you're incubating the virus, you may have a false negative test if you test too early," Dr. Suchindran said. "If you haven't developed symptoms, testing around day five after exposure is ideal."

The general rules behind testing have remained mostly the same throughout the pandemic, Dr. Suchindran said. However, due to the way that the Omicron variant behaves in our bodies, there are a few things to be aware of while you're testing.

With other strains of COVID-19, it was more common for a person to test positive around the time that they developed symptoms. But with newer Omicron subvariants, symptoms start much sooner after you're exposed—its incubation period is typically three to four days—sometimes even before a positive test.

"We're seeing a lot of delayed positivity with testing right now," Amy Karger, MD, PhD, associate professor at the University of Minnesota Medical School, told Health. "People are having symptoms for one to three days with negative tests, and then they'll turn positive after a few days with the COVID testing. And that was not happening with prior variants."

The delayed positivity means it's more difficult to fully trust a negative test result, especially in the first few days, Dr. Karger said.

It's unclear why the delayed positive test results are happening, but researchers have some theories. According to Dr. Karger, one guess is that the Omicron subvariants may replicate more in the throat, so there may not be enough virus for nasal swab COVID-19 tests to detect early on. Another possibility, she added, is that because most people have some level of immunity from a prior infection or a vaccine, those early symptoms may just be our immune system doing its best to fight off the virus.

Whatever the reason, testing negative within the first few days after an exposure doesn't mean you're out of the woods just yet.

"If you get a negative and you've had a recent exposure, and particularly if you have symptoms," said Dr. Karger, "I think the best advice for people is to just treat it like you still have COVID."

In this situation, Dr. Suchindran and Dr. Karger agreed, it may be best to repeat at-home tests and couple it with a PCR laboratory test. Though the turnaround time is a bit slower, PCR tests are more sensitive and may be able to catch the virus in those earlier stages.

"Certainly one approach is to go in for a PCR collection, maybe a couple—one or two days—before you would be recommended to do the at-home tests," Dr. Karger said. "Maybe on day three or four you could get the PCR and then do the at-homes as a second option, and then see what happens. There absolutely are people who have had a negative at-home and then get a positive PCR."

While the main question for many after exposure to COVID-19 is when to test, it's important to remember that there are still guidelines around quarantining after coming into contact with the virus.

The general rule of thumb is for everyone to test five days after exposure, but for people who are unvaccinated, they should stay home and quarantine during that time, according to CDC guidelines.

If you've been exposed to COVID-19, but you're vaccinated or you've had a confirmed case within the past 90 days, you do not need to quarantine while you wait to test, unless you develop symptoms.

Even if you test negative and have no symptoms after five days, it's still recommended that you mask and watch for symptoms.

"The incubation period for COVID-19 can be up to 10 days," said Dr. Sunchindran. "So even after exposure testing is done on day five, it's important to continue to take precautions during the full 10 day incubation period, such as wearing a well fitted mask or avoiding people who may be at risk for severe infection from COVID-19."

And if symptoms do pop up during those 10 days, it's best to test again.

Guidelines for positive tests haven't changed much since early 2022. The CDC recommends that you isolate for five days following a positive test, which applies to everyone regardless of vaccination status. If you do have symptoms but are fever free for 24 hours beforehand, you can also end your isolation after five days. For days six through 10, just like those who were exposed but tested negative, the CDC recommends that you continue to wear a mask in public.

Guidelines have become a bit more confusing as the virus evolves and people fall into different categories of immunity, Dr. Karger said. But, we have the tools we need to determine next steps after an exposure.

"The more you repeat a test and you get the same result, the more confident you can be that that was the correct result. The caveat being of course, this issue of the delayed positivity," she said. "Everyone should keep in mind that you could still turn positive on day three or four."