Some coronavirus tests may yield false positive results for 47 percent of samples, a study summary from China suggests.
In the close contacts of COVID-19 patients, nearly half or even more of the ‘asymptomatic infected individuals’ reported in screening for active nucleic acid tests could be false positive, the authors of Jiaotong University in Xi wrote ‘an, China.
The abstract provides little detail on how these tests were conducted, but the Chinese health authorities were traveling to infected people’s homes and collected samples to test with other members of their household at the height of the outbreak there.
An American expert says the high false positive result may be due to contaminants from poor collection – and warns that comparable rates would be possible if Americans tried to test themselves.
It comes after the U.S. Food and Drug Administration (FDA) has warned that companies should not sell home test kits directly to consumers – although some start-ups in the US have already started shipping them.
Even drive-thru testing can increase the risk of a sample becoming infected for coronavirus testing, and the risks when testing at home could be greater and lead to false positives, a scientist at Columbia University warned after Chinese research suggested that up to 47% of the closing contact tests yielded false positives there
The Chinese research team predicted that about 20 percent of the close contacts of people infected with coronavirus could develop the disease.
But they found that more than 47 percent of the tests were false positive.
A summary of a study has only been posted in the PubMed repository of that National Institutes of Health (NIH), so it’s difficult to determine how many tests this translated or how the study was conducted.
Still, Dr. Susan Whittier, director of microbiology services at Columbia University and New York Presbyterian Hospital, said it underscores just how sensitive and misleading tests can be for COVID-19 if not performed under tightly controlled conditions.
“When we think of false positives, there are really only two steps where this happens,” she told DailyMail.com: during collection or when samples are analyzed in the lab.
In the case of the Chinese tests with an alarmingly high number of false positives: “Maybe they went to the infected people’s houses and tested the people around them.
‘That environment is polluted and the collection of samples really has to be done carefully.
“While they collect samples, they can introduce an environmental virus and those samples would test positive, but that’s because of the way they were collected.”
COVID-19 in particular is at unusually high levels in the body, and thus probably in the environment, compared to other viruses.
Dr Susan Whittier warns that samples may falsely test positive for coronavirus “because of the way they were collected.” Pictured: Healthcare workers collect samples from a drive-thru site
The U.S. has made efforts to speed up testing, and this has led to daily increases in the number of cases and hasty release of home tests before the FDA warned against it
Dr. Whittier said her lab, which runs between 450, needs to boost levels of the virus by a factor of 20 or 30 to detect it.
With coronavirus, they just need to boost it by a factor of 15, “so there’s more virus,” she said.
It is also possible that samples are contaminated in laboratories where they are analyzed.
Labs certified to the level that Dr Whittier’s are at relatively low risk because they must have strict protocols.
While states can now approve their own tests, including those for which samples are taken at drive-thru sites, the samples still need to be analyzed in these rigorous CLIA labs.
False positives ‘are certainly possible … if people use test kits that have not gone through a rigorous validation process,’ said Dr. Whittier.
“Any time you use a kit from an uncertified lab or without FDA approval, I wouldn’t trust any of the results.”
Despite the need for better access to testing, this was one of the concerns with home test kits like Nurx’s, Everlywell.
Dr Susan Whittier warned that the “environmental virus” in rooms with infected people can lead to false positives in their close contacts. This certainly applies to members of the household and can be transferred to vehicles where penetration samples are collected
“ They have good intentions of making testing available to more people, but it’s 180 degrees away from what’s going on in a CLIA lab, ” said Dr. Whittier.
“Making a bad test available does more harm than good.”
In addition, even if the laboratories analyze these results, it is highly unlikely that lay people will be able to sample themselves appropriately, despite the FDA’s announcement that such self-smear will be allowed if it takes place in health care facilities.
Until that announcement, only nasopharyngeal swabs were acceptable, requiring a long Q-tip-like tool to be stuck far into the nostril.
“If you do it right, it’s so uncomfortable that it feels like you’re going for a brain biopsy,” said Dr. Whittier.
“Once it’s uncomfortable, you’re going to stop, and it should be and it should be uncomfortable
“My concern would be someone sitting in a car with their head back
Now, new research from the Bill and Melinda Gates Foundation, UnitedHealth, Quest Diagnostics, and the University of Washington has found that self-swabbing has produced results as accurate as those on swabs taken by clinicians.
The study participants wiped the lower, less difficult part of the nose, a method Dr. Whittier called “promising.”
But she still worries that cotton swabs will be taken outside of relatively sterile clinic environments, they can easily become contaminated.
“If there are hundreds of cars in line, I’m afraid they won’t get a great one,” said Dr. Whittier.
Nearly 60,000 Americans have coronavirus, and more than 800 have died from the infection
“Do they change their gloves? I have seen videos where, after collecting [the sample, the workers] didn’t get it in the tube and it went down the side on their hands.
“There is a lot of potential for contamination, but I haven’t been there personally.”
Some labs found that even the CDC’s original test, which would be the “ gold standard, ” gave false positive results.
Drive-thru testing hasn’t been going on long enough to have solid data on the kits’ false positives, but Dr. Deborah Birx on Wednesday announced that Americans are now allowed to swab in their cars and hand over their samples to health care providers in biosafe bags.
It aims to limit the use of personal protective equipment and exposure for health professionals, but raises even more questions about how pure these samples will be and how accurate the tests will be on them.