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Monday, January 31, 2022 (Kaiser News) – What does it mean if a person’s rapid antigen test returns positive after five days of isolation due to covid-19? According to experts, this person is probably still carrying a viral load, high enough to infect others.
“Every time you test positive for one of these quick tests for covid at home, it means you still have a really high level of viral protein and most experts interpret this as a high level of virus present in your nasal passage,” he said. Matthew Biniker, director of clinical virology at the Mayo Clinic and president of the Pan American Society of Clinical Virology.
The Biden administration is buying a billion tests for fast antigens to be delivered to American homes to meet the need for increased covid testing and alleviate the shortage of tests across the country. This influx of tests comes after the revised federal guidelines, which shorten the period of isolation to five days after the onset of symptoms or a positive test, followed by five days of masking.
It is well known that PCR tests, highly sensitive polymerase chain reaction tests that detect viral genetic material, can detect “dead” virus – material that cannot be replicated – and give a positive result within weeks of recovery. , even when the person being tested is no longer infected.
But virologists say this is unlikely to happen with rapid antigen tests – which detect certain proteins in the virus and give results within 30 minutes – which target human mailboxes.
The chances are very low, outside of laboratory conditions, that someone who gets a positive result from a quick antigen test will be a non-infectious person who releases large amounts of dead virus, said Kelly Wroblewski, director of infectious disease programs at the Public Health Laboratories Association.
There are several reasons for this. First, according to the American Society of Infectious Diseases, the “main advantage” of rapid antigen tests is that they are somewhat blunt tools to catch the virus. Therefore, a positive result usually means that the person has a high viral load, especially if symptoms occur.
To be continued
Second, a significant amount of viral material is needed to register as positive in an antigen test, so a person will need a high level of dead virus in his nose or throat, and this usually signals a high level of live virus. .
Third, even if someone does have a high level of dead virus, the amount alone would not be enough to trigger a positive test – viral proteins tend to lose their shape after a battle with the immune system, which can make them undetectable by antigen tests.
In the laboratory, a rapid antigen test can detect particles of a “dead” virus, said Dr. Sam Dominguez, a pediatric infectious disease physician and medical director of the Clinical Microbiology Laboratory at Colorado Children’s Hospital.
Federal-funded scientists have done just that to test whether rapid antigen tests will work as well on omicron as other covid variants. However, Dominguez said, the chances of a dead virus – and only a dead virus – causing a positive antigen test in humans, rather than in a petri dish, are low.
Unlike scientists in the laboratory, the human body in attack mode is not just trying to deactivate viruses. He tries to erase them, the proteins and everything else. “RNA can last longer than proteins,” said Wroblewski, but none of the substances are known to be strong. Even for scientists, it’s like the art of keeping proteins intact after inactivating the virus.
“It’s not easy,” said Dr. Isabella Ragan, a veterinarian at Colorado State University who has branched out into human virology and has been working for about two years to develop a vaccine against SARS-CoV-2. Its work depends on killing the virus while maintaining the shape of its proteins.
The confusion over how to interpret test results stems in large part from this conundrum: although there are plenty of testing options available, there is no reliable way to judge whether a person is actually contagious.
“I wish there was,” Biniker said. “There is no test for infectivity that we have.
To be continued
The best option is to take a sample from a patient, place it on a plate of thriving living cells, and see what happens to healthy cells. If there is a live virus, says Dirk Dietmer, a virologist at the University of North Carolina-Chapel Hill, “then the cells will die, just as the lung cells in your body would die. But the picky process takes about three days and can only be performed in laboratories that have failed to deal with such pathogens, making it impractical.
Instead, the most widely available tests rely on completely different methods. They fall into two categories, commonly called molecular tests and antigen tests.
Molecular tests, including PCR, look for specific bits of RNA in the virus. With the exception of a few over-the-counter options, the tests are processed in a laboratory. They are able to detect small pieces of the genetic material of the virus by copying everything that spins in a person’s sample over and over again, amplifying it “a million to a trillion times,” said Dr. Marie Louise Landry, director of the laboratory. clinical virology at Yale New Haven Hospital. Therefore, she explained, “PCR can detect very low levels of viral RNA for weeks and even months after infection, when the patient is no longer infected.”
Rapid antigen testing, on the other hand, looks for viral proteins, not the genetic material of the virus. Many are looking for a nucleocapsid or “N” protein that is abundant in infected cells and forms a protective capsule around the genetic material of the virus. Unlike molecular tests, rapid antigen tests only work with what is available – no copying or amplification. These tests drag a person’s sample through a special piece of paper that contains a fence of antibodies designed to capture the N proteins of the virus. If enough protein is attached to the fence, a visible colored line will appear.
“Even single molecules can give a positive PCR result,” said Dr. Michael Mina, an epidemiologist who was a vocal supporter of rapid testing during the pandemic and is now the chief research officer of eMed. But, he added, “about 100,000-1,000,000 molecules are needed to get a positive rapid antigen test.”
To be continued
But what about the official recommendation that people with covid should be isolated for five days at home – followed by five days of disguise? Data from the world of sport, where resources and testing methods abound, provide insight into how variable this period of contagion can be.
A preliminary study of NBA players and officials found that among 70 people infected with omicron, by day 5 after their first positive test, about 40 percent were still likely to be contagious.
“What we recommend is to do an antigen test between 5 and 10 days. If it’s positive, you stay in isolation until day 10, “Biniker said.
CDC Public Affairs Specialist Jasmine Reed said the best approach is to use an antigen test at the end of the five-day isolation period if the person’s symptoms improve. “If your test is positive, you should continue to isolate yourself until day 10,” she said.
Wroblewski said an important criterion for contagion is the simplest: how someone feels.
“If you have a fever and a cough, don’t go see people. “I have a feeling that we have somehow forgotten this part,” she said. “Let’s not put so much emphasis on testing and technology that we forget basic infection control practices: if you’re sick, stay home.
KHN (Kaiser Health News) is a national newsroom that produces in-depth journalism on health issues. Along with policy analysis and surveys, KHN is one of the three main operational programs of KFF (Family Foundation Kaiser). KFF is a gifted non-profit organization that provides information on the nation’s health issues.
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