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COVID-19 rapid tests can breed confusion; here’s how to make sense of the results

Technique is important when it comes to obtaining a sufficient amount of virus for a rapid test. Images by Tang Ming Tung/Digital Vision via Getty Images

As temperatures drop, cold and flu season hits, and vacation travel picks up, people will no doubt have questions about COVID-19 testing. Is this the year people can finally return to large gatherings for traditional celebrations? What role does testing play in deciding whether to go out or stay at home?

Adding to the confusion are personal accounts of people experiencing confusing or seemingly conflicting test results.

We are part of a team that has been developing and testing SARS-CoV-2 tests since the beginning of the pandemic. Additionally, some of us are infectious disease specialists with decades of experience.

Our insights from both the cutting-edge of rapid test research and our clinical perspectives from working directly with patients can help people figure out how best to use rapid tests.

Several negative tests, then one positive – why?

SARS-CoV-2, the virus that causes COVID-19, takes time to build up in the body like many other viruses and bacteria that cause respiratory diseases. It usually takes two to three days to test positive after exposure. Our research group has shown this, as have others.

Rapid tests detect parts of the virus that are present in the sample taken from the nose or mouth. If the virus hasn’t replicated high enough in that part of your body, a test will be negative. Only when the amount of virus is high enough will a person test positive. For most Omicron variants in circulation today, this is one to three days, depending on the initial amount of virus you are exposed to.

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A news anchor quickly tests for COVID-19 on live television.

Why do some people test positive for a longer period of time?

It is important to clarify what kind of test we are talking about in this situation. Studies have shown that some people can test positive for a month or more with a PCR test. There are two reasons for this: PCR tests are able to detect extremely small amounts of genetic material, and fragments of the virus can remain in the airways for a long time before being cleared.

Regarding rapid tests, there are reports that some individuals have tested positive for longer periods of time with the current strains of the omicron variant compared to previous variants. Several studies show that most people stop testing positive five to seven days after their first positive test, but between 10% and 20% of people continue to test positive for 10 to 14 days.

But why it takes some people longer to clear the virus than others is still unknown. Possible explanations include a person’s vaccination status or the ability of their own immune system to clear the virus.

Additionally, a small number of people treated with the oral antiviral drug Paxlovid have tested negative on rapid antigen tests with no symptoms, only to “recover” seven to 14 days after their first positive test. In these cases, symptoms sometimes recur or even occasionally worse than before, along with positive rapid test results. People experiencing this should re-isolate as evidence has shown that people with rebound cases can spread the virus to others.

Why do I have COVID-19 symptoms but the test is still negative?

There are several possible explanations for why you might get negative rapid tests even if you have COVID-like symptoms. The most likely thing is that you have an infection with something other than SARS-CoV-2.

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Many different viruses and bacteria can make us sick. As mask requirements have been lifted in most settings, many viruses that were not widespread during the pandemic, such as influenza and respiratory syncytial virus or RSV, are re-spread and making people sick.

Second, mild COVID-19 infection in a vaccinated and boosted person can result in virus levels high enough to cause symptoms but too low to result in a positive rapid test.

Finally, using poor technique when sampling from the nose or mouth can result in too little virus being present to give a positive test. Many nasal swab tests require you to swab in each nostril for at least 15 seconds. Failure to take the swab according to package directions can result in a negative test result.

Our previous studies show that if you are symptomatic and have two rapid antigen tests 48 hours apart instead of just one, you are more likely to test positive if you are infected with SARS-CoV-2.

Self-smear: Sounds a bit spasmodic, but it’s not that bad.

Do rapid tests work against the current strains of SARS-CoV-2?

Several studies have examined the performance of rapid tests against the Omicron variant.

Fortunately, these studies show that all emergency rapid tests approved by the U.S. Food and Drug Administration detect current Omicron variants just as well as previous variants like Alpha and Delta. If a symptomatic person tests positive on a rapid test, they likely have COVID-19. If you are exposed to someone who has COVID-19 or have symptoms but get a negative test, you should take another test within 48 hours. If you then test positive or your symptoms worsen, contact your doctor.

What is the best way to use and interpret rapid tests before meetings?

Testing remains an important tool to identify infected individuals and contain the spread of the virus. It’s still a good idea to do a quick test before visiting people, especially the elderly and those with compromised immune systems.

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If you think you may be infected, the FDA recently updated their testing guidelines based largely on data collected by our lab. The testing schedule that is most likely to help you determine if you are infected is to have two tests 48 hours apart if you have symptoms. If you have no symptoms, do three tests, one every 48 hours.

Does a positive test mean you can spread COVID to others?

The Centers for Disease Control and Prevention recommends that if you test positive for COVID-19, you should stay home and isolate yourself from others for at least five days from the date of your positive test. People are probably most contagious during those first five days. After you have finished the isolation and are feeling better, you should do a quick test again.

If you have two negative tests 48 hours apart, you are most likely no longer contagious. If your rapid tests are positive, you can still be contagious even if you’re past day 10 of your positive test. If possible, you should wear a mask. Several studies have shown a correlation between when a person tests positive on a rapid test and when live virus can be collected from a person, which is a common way to tell if someone is infectious.

Testing remains an important tool to protect people from COVID-19 and avoid transmission to others. Knowing your status and choosing to get tested is a decision individuals make based on their own risk tolerance associated with contracting COVID-19.

People who are older or at higher risk of serious illness may want to test frequently after exposure or when they have symptoms. Some people may also be concerned about having COVID-19 and spreading it to others who may be at higher risk of hospitalization. Combined with other measures like getting vaccinated and staying home when you’re sick, testing can reduce the impact of COVID-19 on all of our lives in the coming months.The conversation

This article was republished by The Conversation under a Creative Commons license. Read the original article.

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