Day 6 of COVID and a Rapid Test Comes Back Positive … Stay Home

By Rae Ellen Bichell

Monday, January 31, 2022 (Kaiser News) — What does it imply if an individual’s fast antigen check consequence comes again optimistic after 5 days of isolation attributable to covid-19? According to the consultants, that particular person is almost definitely nonetheless carrying a viral load excessive sufficient to contaminate others.

“Anytime you’re positive by one of these rapid at-home covid tests, it means that you’ve still got a really high level of the viral protein, and most experts are interpreting that as a high level of virus present in your nasal passage,” mentioned Matthew Binnicker, director of scientific virology on the Mayo Clinic and president of the Pan American Society for Clinical Virology.

The Biden administration is shopping for a billion fast antigen exams to ship to American properties, aiming to deal with the necessity for elevated covid testing and ease a nationwide scarcity of exams. That inflow of exams comes on the heels of revised federal pointers that shortened the isolation interval to 5 days after signs began or a optimistic check, adopted by 5 days of masking.

It’s broadly recognized that PCR exams, the extremely delicate polymerase chain response exams that detect viral genetic materials, can decide up “dead” virus — materials not able to replicating — and yield a optimistic consequence for weeks after restoration, even when the particular person being examined is not infectious.

But virologists say that’s unlikely to be the case for the fast antigen exams — which detect sure proteins within the virus and produce outcomes inside half-hour — which might be headed for individuals’s mailboxes.

The odds are very slim, exterior of a laboratory setting, that somebody who will get a optimistic consequence on a fast antigen check is a non-infectious particular person shedding massive quantities of lifeless virus, mentioned Kelly Wroblewski, director of infectious illness applications for the Association of Public Health Laboratories.

There are a number of causes for this. First, based on the Infectious Diseases Society of America, “a major advantage” of fast antigen exams is that they’re considerably blunt instruments for choosing up on the virus. Therefore, a optimistic consequence tends to imply the particular person has a excessive viral load, particularly if signs appeared.

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Second, it takes a considerable quantity of virus materials to register as optimistic on an antigen check, so an individual would wish a excessive stage of lifeless virus sitting round of their nostril or throat, and normally that alerts a excessive stage of reside virus, too.

Third, even when somebody did have a excessive stage of lifeless virus hanging round, amount alone wouldn’t be sufficient to set off a optimistic check — viral proteins are likely to lose their form after a battle with the immune system, which might render them undetectable by antigen exams.

In a laboratory setting, a fast antigen check may detect bits of “dead” virus, mentioned Dr. Sam Dominguez, a pediatric infectious illness physician and the medical director of the scientific microbiology lab at Children’s Hospital Colorado.

Federally funded scientists did simply that to test whether or not fast antigen exams would work as nicely on omicron as they did on different covid variants. However, Dominguez mentioned, the chances of lifeless virus — and lifeless virus alone — triggering a optimistic antigen check in a human moderately than a petri dish are low.

Unlike scientists in a lab, the human physique in assault mode isn’t attempting to inactivate viruses simply so. It’s attempting to obliterate them, proteins and all. “RNA can last longer than the proteins,” mentioned Wroblewski, however neither substance is thought for durability. Even for scientists it’s considerably of an artwork to maintain proteins intact after inactivating the virus.

“It is not easy,” mentioned Dr. Izabela Ragan, a veterinary scientist at Colorado State University who has branched into human virology, and who has labored for about two years on creating a vaccine towards SARS-CoV-2. Her work hinges on killing the virus whereas preserving the form of its proteins.

The confusion round how you can interpret check outcomes stems largely from this conundrum: While there’s a wealth of testing choices out there, there isn’t a foolproof method to gauge whether or not an individual is definitely infectious.

“I wish there was,” mentioned Binnicker. “There is no test that we have for infectiousness.”

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The most suitable choice is to take a affected person’s pattern, stick it in a dish of thriving dwelling cells, and see what occurs to the wholesome cells. If there’s reside virus, mentioned Dirk Dittmer, a virologist on the University of North Carolina-Chapel Hill, “then the cells would die, just like the lung cells in your body would die.” But the finicky course of takes about three days and could be executed solely in labs cleared to deal with such pathogens, rendering it impractical.

Instead, essentially the most broadly out there exams depend on completely completely different strategies. They fall into two classes, sometimes referred to as molecular exams and antigen exams.

Molecular exams, together with PCR, search for particular bits of the virus’s RNA. With the exception of some over-the-counter choices, the exams are processed in a lab. They are able to detecting tiny bits and items of the virus’s genetic materials by copying no matter is floating round in an individual’s pattern again and again, amplifying it “a million- to a trillion-fold,” mentioned Dr. Marie Louise Landry, director of the Clinical Virology Laboratory at Yale New Haven Hospital. That’s why, she defined, “PCR can detect very low levels of viral RNA for weeks and even months after infection, when a patient is no longer infectious.”

Rapid antigen exams, then again, search for viral proteins moderately than the virus’s genetic materials. Many of them search for nucleocapsid or “N” proteins, that are plentiful in contaminated cells and type a protecting capsule across the virus’s genetic materials. Unlike molecular exams, fast antigen exams work solely with what’s out there — no copying or amplifying concerned. These exams drag an individual’s pattern throughout a particular piece of paper that comprises a fence of antibodies designed to seize onto the virus’s N proteins. If sufficient proteins snag on the fence, a visual line of coloration will seem.

“Even single molecules can turn a PCR positive,” mentioned Dr. Michael Mina, an epidemiologist who has been a vocal supporter of fast testing all through the pandemic and is now chief science officer for the well being care firm eMed. But, he added, it takes “about 100,000-1,000,000 molecules to turn the rapid antigen test positive.”

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But what in regards to the official advice that individuals with covid ought to isolate for 5 days at dwelling — adopted by 5 days of masking? Data from the world of sports activities, the place assets and testing strategies abound, supply a glimpse into how variable that interval of infectiousness could be.

A preliminary research of NBA gamers and staff discovered that amongst 70 individuals contaminated with omicron, by Day 5 after their first optimistic check about 40% of them had been nonetheless seemingly infectious.

“What we’re recommending is that between Days 5 and 10, you can take an antigen test. If it’s positive, you stay in isolation till Day 10,” mentioned Binnicker.

CDC public affairs specialist Jasmine Reed mentioned the most effective method is to make use of an antigen check towards the top of the five-day isolation interval if the particular person’s signs have improved. “If your test result is positive, you should continue to isolate until Day 10,” she mentioned.

Wroblewski mentioned an necessary gauge of contagiousness is the only: how somebody is feeling.

“If you have a high fever and a cough, don’t go see people. I feel like we somehow forgot that part,” she mentioned. “Let’s not put so much emphasis on the test and the technology that we forget basic infection control practices: that if you’re sick, stay home.”

KHN (Kaiser Health News) is a nationwide newsroom that produces in-depth journalism about well being points. Together with Policy Analysis and Polling, KHN is without doubt one of the three main working applications at KFF (Kaiser Family Foundation). KFF is an endowed nonprofit group offering data on well being points to the nation.

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