Julie Ann Justo, an infectious disease clinical pharmacist for a South Carolina hospital system, hoped that Christmas week would finally be the time her family could safely reunite.
Before the celebration, eligible family members were vaccinated and had their boosters. They isolated themselves and wore masks. And many relied on the negative results of the rapid covid tests that were done before the meeting that called 35 people in the South Florida.
But in less than a week, Fair and at least 13 family members tested positive for covid, with many experiencing typical symptoms of an upper respiratory virus, such as a sore throat and runny nose.
Like many others, Justo’s family learned the hard way that a single negative result from a home test is no guarantee that a person is not sick or does not carry the virus.
That is even more true with the omicron variant, which is highly contagious. Testing can be done too early, before enough virus is present to detect it, or too late, after a person has already infected others.
And most tests are supposed to they should be used in pairs, to take two tests a few days apart each. But many brands carry only one kit, and the cost plus scarcity means that many get only one test.
Although experts say that home antigen tests are still a useful tool, they add that they can provide false confidence.
Some people mistakenly view home tests “as a freedom card,” said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University School of Medicine , in Nashville, Tennessee. “I’m negative, so I don’t have to worry anymore”.
“Omicron is so transmissible that it’s a challenge to use any kind of testing strategy in terms of going or not going to meetings and being successful ,” said Dr. Patrick Mathias, vice president of clinical operations in the department of laboratory medicine and pathology at the University of Washington School of Medicine.
Rapid tests are quite good at correctly detecting infection in people with symptoms, Mathias added, with an accuracy range of 70% to almost 90%, an estimate from several studies.
Other investigations, some prior to the circulation of the Current variants or those performed in more controlled settings have shown higher rates, but tests may still miss some infected people.
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This increases the risk of spread, and the possibility grows dramatically depending on the number of people attending an event.
Rapid tests are less accurate in people without symptoms.
For asymptomatic patients, rapid tests “on average, correctly detect the infection approximately 50% of the time,” said Shama Cash-Goldwasser, an advisor to Prevent Epidemics at Resolve to Save Lives, a nonprofit group led by former CDC Director Tom Frieden.
Looking back, Justo said his family did everything they could, but acknowledges that two things put them at greater risk: Not all family members were tested before getting together due to a shortage of kits. And there were several children under the age of 5 who are not yet eligible for the vaccine. Later, they were among the first to show symptoms.
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“We probably rely too much on negative rapid tests to meet indoors, without other layers of protection,” he said.
“One critical thing is the timing of the test” Schaffner said. If the test is done too soon, such as a day or two after exposure, the results may not be accurate. Similarly, testing several days before an event will not tell much about who may be infectious on the day of the party.
Schaffner et al recommend starting testing three days after a known exposure or , if one feels sick, a few days after the onset of symptoms. It is always a good idea to use both tests in the kit, according to the instructions, the second one from 24 to 36 hours after the first. For an event, make sure one of the tests is done on the day of the event.
Antigen tests work by looking for specific proteins of the viruses, which must be present in adequate numbers for the test to detect them. (Laboratory PCR tests are more accurate because they can detect smaller amounts of the virus, but they take longer to return results).
Covid markers can remain as remnants long after the virus is alive has disappeared, so some scientists question the use of tests, whether antigen or PCR, as a measure to know when patients can end their isolation, particularly if they seek to shorten the recommended period.
The CDC recommends five days of isolation, which can end if symptoms clear or resolve, without fever.
Some patients will test positive 13 days or more after the first symptoms, although it is unlikely that they will still be infectious by then.
Still, that means many people are using rapid tests inappropriate, not just relying too much on them as or protection against covid, but also as an indicator of when an infection has ended.
Rapid home tests should be used for several days to increase the chances of obtaining an accurate result.
“Each individual test doesn’t have as much value as serial tests,” said Dr. Zishan Siddiqui, medical director of the Baltimore Convention Center Field Hospital and assistant professor of medicine at Johns Hopkins University. And, because the test is less accurate in people without symptoms, he said asymptomatic people shouldn’t rely on a single rapid test to reunite with friends or family without other mitigation measures.
One study examined to 30 adults vaccinated in December of 2021 . “Most omicron cases were infectious for several days before becoming detectable by rapid antigen tests,” the study found. The research has not yet been peer-reviewed.
False negatives are also more likely when there is community spread and circulation of the virus is rampant, as is now the case in most states.
“If there is a lot of community spread, that increases the likelihood that you will have covid,” Cash-Goldwasser said. However, the tests, statistically, will still miss a certain percentage of those actually infected. With a higher number of people likely to be infected, and the same percentage chance of missing cases, the absolute number of false negatives increases, he explained.
So, right now, “if you have a negative , it is important to be more suspicious”, he said.
Vaccines, boosters, the use of masks, social distancing, ventilation and separate tests are imperfect solutions to prevent infections. But layered, they can serve as a more effective barrier, Schaffner said.
“The rapid test is helpful,” his own family used them before getting together for Thanksgiving and Christmas, “but it’s a barrier with holes,” he added.
The Justo family tried those layers, but there were holes left through which the virus passed. While most family members had mild symptoms, Justo said she felt short of breath, felt fatigued, and had headaches, muscle aches, and nausea. It took a few 10 days before she felt better.
“I certainly spent a lot of time reviewing what we could have done differently, but the reality was that we did the best we could,” Justo said. “Fortunately no one needed to go to the hospital, and I attribute that to the vaccinations. For that I am grateful.”
KHN (Kaiser Health News) is the newsroom of KFF (Kaiser Family Foundation), which produces in-depth journalism on health issues. Along with Policy Analysis and Surveys, KHN is one of the three main programs of KFF. KFF is a nonprofit organization that provides health information to the nation.