Tuesday, September 22, 2020

Ohio governor tested negative hours after positive COVID-19 test. How can that happen?


Hours before Ohio Gov. Mike DeWine was scheduled to meet with President Donald Trump on Thursday, he was tested for the novel coronavirus as part of White House protocol.

Much to his surprise, he tested positive despite not having any other symptoms besides a headache, media outlets reported. But hours later, DeWine tested negative two separate times.

Turns out the governor received two different types of tests, the first of which is a cheaper, quicker yet more inaccurate alternative to the test the majority of Americans receive, and the one responsible for result delays of up to two weeks.

“In a second COVID-19 test administered today in Columbus, Governor Mike DeWine has tested negative for COVID-19. First Lady Fran DeWine and staff members have also all tested negative,” the governor’s office tweeted. “We feel confident in the results from Wexner Medical Center. This is the same PCR test that has been used over 1.6 million times in Ohio by hospitals and labs all over the state.”

To date, there are two types of COVID-19 diagnostic tests: a molecular test and an antigen test. Both of them can reveal if someone has an active coronavirus infection, but they differ in what they look for.

Antigen tests

Antigens are proteins that cause an immune system to produce antibodies. If there are enough of them present in a person’s biological sample such as a nasal or throat swab, they will attach to specific antibodies that are fixed on a paper strip, and “generate a visually detectable signal, typically within 30 minutes,” according to the World Health Organization.

In other words, antigen tests look for specific proteins found on the surface of the coronavirus to determine if someone has an active infection. The tests are also available for other illnesses such as strep throat, influenza, tuberculosis and HIV.

But how well they work depends on when during one’s illness the test is administered, the concentration of the virus in the sample, the quality of the sample and the “precise” mixture of liquids used in the chemical analysis in the test kit, the WHO said.

Although antigen tests are usually cheaper and return results faster, they have a sensitivity that varies between 34% to 80%, according to the group, meaning “half or more of COVID-19 infected patients might be missed by such tests.” Results from these tests usually need to be confirmed with a molecular exam.

False-positive results with antigen tests — as what happened with Gov. DeWine — are less common than false-negatives, the U.S. Food and Drug Administration says, but they can occur if the antibodies on the test strip also recognize those of other coronaviruses, like those that cause the common cold.

“These tests represent a new technology to reduce the cost and improve the turnaround time for COVID-19 testing, but they are quite new,” DeWine’s office tweeted. “We do not have much experience with antigen tests here in Ohio. We will be working with the manufacturer to have a better understanding of how the discrepancy between these two tests could have occurred.”

Some test positive for COVID-19 twice. So why do experts say reinfection is unlikely?

The WHO “does not currently recommend” antigen diagnostic tests, but if further research “demonstrates adequate performance,” then they could possibly be used to reduce or eliminate the need for expensive molecular tests that take too long to identify infected individuals.

“What everyone wants is for a test to be cheap, accurate and fast,” Geoffrey Baird, a laboratory medicine specialist at the University of Washington in Seattle, told Science Magazine. “You can only ever have two of those.”

Molecular tests

Molecular tests, also known at RT-PCR tests, look for the coronavirus’ specific genetic material, leading to better sensitivity than antigen tests and “highly accurate” results, the FDA said.

Administered to the majority of Americans, they are more costly, usually require a medical professional and can take up to one week — or two in regions experiencing a backlog due to rapid viral spread — to return results. The delays make it easier for potentially infected people to spread the disease to others.

Several studies show molecular tests are accurate about 95% or more of the time. However, the FDA warns that “no test is 100% accurate all of the time.” Many factors could affect the test’s accuracy such as contaminated swabs and improper storage and swab collection.





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