As fall temperatures settle in, cold and flu season gets into full swing, and vacation travel increases, people will no doubt have questions about testing for COVID-19. Is this the year that people can finally return to the big gatherings for traditional celebrations? What role does evidence play in deciding whether to go out or stay 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 early days of the pandemic. Also, some of us are infectious disease specialists with decades of experience.
Our insights, both from the forefront of rapid test research and from our clinical perspectives from working directly with patients, can help people discover how to make the best use of rapid tests.
SARS-CoV-2, the virus that causes COVID-19, takes time to accumulate in the body, like many other viruses and bacteria that cause respiratory illness. It usually takes two to three days to test positive after exposure. Our research group has shown it, as have others.
Rapid tests detect parts of the virus that are present in the sample collected from your nose or mouth. If the virus has not replicated to a high enough level in that part of your body, the test will be negative. Only when the amount of virus is high enough does a person’s test become positive. For most of the omicron variants in circulation today, this is one to three days, depending on the initial amount of virus you are exposed to.
Why do some people test positive for long periods of time?
It is important to clarify what type 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. The reason for this is twofold: PCR tests are capable of detecting extremely small amounts of genetic material, and fragments of the virus can remain in the respiratory system for a long time before being eliminated.
When it comes to rapid tests, there are reports that some people test positive for a prolonged period with current strains of the omicron variant compared to earlier variants. Various studies show that most people no longer test positive after five to seven days from their first positive test, but 10% to 20% of people continue to test positive for 10 to 14 days.
But why some people take longer to clear the virus than others is still unknown. Possible explanations include a person’s vaccination status or the immune system’s ability to clear the virus.
In addition, a small number of people who have been 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 initial positive test. In these cases, people sometimes experience symptoms that recur or are even worse than before, along with positive rapid test results. People who experience this should self-isolate again, as it has been shown that people with rebound cases can spread the virus to others.
There are several possible explanations for why you may get negative rapid tests even when you have COVID-like symptoms. You most likely have an infection from something other than SARS-CoV-2.
Many different viruses and bacteria can make us sick. As mask mandates have been lifted in most settings, many viruses that did not circulate widely during the pandemic, such as influenza and respiratory syncytial virus, or RSV, are becoming common again and making people sick. .
Second, a mild COVID-19 infection in a person who has been vaccinated and boosted can result in a viral level high enough to cause symptoms, but too low to test positive on a rapid test.
Finally, using poor technique when taking samples from your nose or mouth can result in too little virus to test positive. Many nasal swab tests require you to swab for at least 15 seconds in each nostril. Failure to take the swab according to package directions could result in a negative test.
Our previous studies show that if you have symptoms and take 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.
Multiple studies have examined the performance of rapid tests against the omicron variant.
Fortunately, these studies show that all of the rapid tests that have been authorized for emergency use by the US Food and Drug Administration detect current omicron variants as well as older variants such as alpha and delta. If a symptomatic person tests positive on a rapid test, he or she likely has COVID-19. If you are exposed to someone who has COVID-19, or have symptoms but receive a negative test, you should get another test in 48 hours. If you later test positive or if your symptoms worsen, contact your health care provider.
Tests before meetings
Testing remains an important tool to identify infected people and limit the spread of the virus. It’s still a good idea to get a quick test before visiting people, especially the elderly and those with weakened immune systems.
If you think you may be infected, the FDA recently updated its testing guidance largely based on data collected by our lab. The most likely testing regimen to identify if you are infected is to perform two tests 48 hours apart if you have symptoms. If you don’t have symptoms, get three tests, one every 48 hours.
The Centers for Disease Control and Prevention recommends that if you test positive for COVID-19, you should stay home for at least five days from the date of your positive test and isolate yourself from others. People are likely to be most infectious during these first five days. After you finish isolation and feel better, consider going back for a rapid test.
If you have two negative tests 48 hours apart, you are most likely no longer infectious. If your rapid tests are positive, you may still be infectious, even if you are past day 10 after your positive test. If possible, you should wear a mask. Multiple studies have shown a correlation between when an individual tests positive on a rapid test and when live virus can be collected from a person, which is a common way to determine if someone is infectious.
Testing remains an important tool to keep people safe from COVID-19 and from spreading it to others. Knowing your status and deciding to get tested is a decision people make based on their own risk tolerance for contracting COVID-19.
People who are older or at higher risk for severe illness may want to be tested often after an exposure or if they have symptoms. Some people may also be concerned about having COVID-19 and spreading it to others who may be at higher risk for hospitalization. When combined with other measures, such as vaccination and staying home when sick, testing can reduce the impact of COVID-19 on all of our lives for months to come.
The Conversation is an independent, nonprofit news organization whose articles are written by academic experts and republished under a Creative Commons license.