California officials warn of misleading COVID test results

Home coronavirus screening has become a way of life for many Californians, but some medical experts are now warning that one test may not be enough to definitively determine if someone is infected.

Health officials stress that home testing is an important and accurate way of tracking COVID-19 infections, but an initially negative test doesn’t mean people are out of the woods.

The US Food and Drug Administration last week suggested that those checking to see if they are infected should take multiple tests over a period of days.

“If you take a COVID-19 antigen test at home and get a positive result, the results are usually accurate,” government officials wrote in a public statement. “However, if you do a COVID-19 antigen test at home, you could get a false negative result.”

Because of this, the agency recommends “repeat testing after a negative result, whether or not you have COVID-19 symptoms.”

The risk of misleading results appears to be higher in symptomatic individuals infected with the latest dominant Omicron subvariant, BA.5, than in previous versions. Experts say this further underscores the importance of follow-up testing.

“If your first antigen home test is negative, we recommend repeating it within 24 to 48 hours,” said Dr. Ralph Gonzales, an associate dean of UC San Francisco, during a recent campus town hall.

Gonzales said he’s noticed an additional delay in how long it takes for a rapid test to turn positive after symptoms appear — especially early on.

according to dr Peter Chin-Hong, an infectious disease expert at UC San Francisco, says some people don’t test positive with rapid tests until four or five days after they show symptoms.

“It’s very common these days,” he said.

Rapid at-home COVID-19 tests are expected to detect at least 80% of coronavirus infections, according to the FDA. In contrast, a laboratory-based PCR test is generally expected to detect the virus 95% of the time someone is infected.

However, PCR tests can take a day or more to process, while rapid test results are available within 15 minutes.

If you have COVID-19 symptoms and get a negative rapid test result, the FDA suggests retaking the test 48 hours later. If the second test is negative and you’re still concerned your symptoms are caused by COVID-19, the FDA suggests either a third rapid test or a lab-based PCR test.

“People should do multiple tests over a period of time, e.g. B. two to three days, especially if the people using the tests do not have any COVID-19 symptoms,” the agency said in its statement. “The FDA emphasizes the continued need for repeat or serial testing when people with a home COVID-19 antigen test have a negative result, including recommending additional testing over a longer period of time.”

There are a number of reasons why some people take longer from the onset of symptoms to testing positive with a rapid test.

The family of omicron variants is generally more likely to start with an infection in the throat, Chin-Hong said, meaning it “takes a while to get to the nose.”

So if you just swab your nose during a test, “and you have a sore throat, it may mean you don’t get the virus there yet,” he said.

Another possible reason is that the immune systems of people who have been vaccinated and boosted are more likely to detect exposure to the coronavirus quickly and trigger symptoms early on to ward off disease, but before the virus levels in the body are high enough for a rapid test recognize.

Before nationwide vaccinations, it took the immune system a relatively long time to recognize the coronavirus and trigger an immune response.

But “in a vaccinated and boosted person, immune cells are already floating around to recognize the enemy. And when you get infected, the immune system activates much faster,” Chin-Hong said. “Now the immune system says, ‘Hey, something’s going on!’ and you start to feel sick, but actually there isn’t much virus around.”

As a result, in a vaccinated and refreshed person, the body can quickly sound its own alarm indicating that COVID-19 has arrived, but it may take longer for a rapid test to detect enough virus.

Whatever the reason, any potential delay in confirming a coronavirus infection is all the more reason for residents to heed one of the most-quoted public health mantras of the last two and a half years: stay home, when you feel sick.

“If you have symptoms of respiratory illness, if you have symptoms that you think may be indicative of COVID, please, please, please stay home,” said Los Angeles County Public Health Director Barbara Ferrer. “Use these rapid tests; They’re generally pretty reliable. But if you still have symptoms and test negative, go ahead and get a PCR test.”

If you get a negative PCR test result and are still symptomatic, you should contact your doctor, Ferrer said.

“But no matter what you’re infected with, until you’re better, don’t embarrass others,” she said during a recent briefing.

If you don’t have COVID-19 symptoms but think you’ve been exposed to the coronavirus, the FDA suggests getting at least three negative rapid test results every 48 hours. If you are still concerned, you can do a fourth rapid test after another 48 hours or have a PCR test done.

Some people might say they’ve tested negative repeatedly, but they actually do a rapid test, say, at 10 a.m. and then 2 p.m., which doesn’t really help people figure out their true infection status, Ferrer said. Testing 24 to 48 hours later provides more meaningful information, she said.

“Diagnostic testing remains a cornerstone in our nation’s fight against COVID-19,” the FDA said in its statement. “While not perfect, at-home COVID-19 antigen testing offers a quick and convenient COVID-19 testing option.” California officials warn of misleading COVID test results

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