Experts say coronavirus positivity rate in US is high because tests are ‘too sensitive’

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Up to 90% of people tested for COVID-19 in Massachusetts, New York and Nevada in July carried virtually no evidence of the virus and that could be because today’s tests are “too sensitive” , according to experts.

Health experts say PCR tests – the most widely used diagnostic test for COVID-19 in the United States – are too sensitive and must be adjusted to exclude people who have insignificant amounts of the virus in their systems because they are probably not contagious.

Today, the PCR test, which provides a yes or no answer if a patient is infected, does not say how many viruses a patient has in their body.

PCR tests analyze the genetic material of the virus in cycles and tests today typically take 37 or 40 cycles, but experts say that is too high because it detects very small amounts of the virus that does not show risk.

Doctors say fewer cycle thresholds – the number of cycles it takes to detect the virus – target those who have a higher amount of the virus and who are at risk, according to the New York Times.

The coronavirus death rate may be low compared to the high infection rate, as standard tests diagnose large numbers of people who may be carriers of “relatively insignificant” amounts of the virus, experts say

Today, there are 5.9 million cases of COVID-19 in the United States and there are more than 182,000 deaths.

The United States recorded 45,604 new cases of the coronavirus on Thursday. If contagiousness rates in Massachusetts and New York were to apply nationally, that would mean that only about 4,500 of those people might need to self-isolate and participate in contact tracing.

As of Sunday, the United States had a daily positivity rate of 8.62%, according to Johns Hopkins. The World Health Organization has said countries that have conducted extensive testing for COVID-19 should stay at 5% or less for at least 14 days before reopening.

Researchers say the solution is the even more widespread use of rapid tests with an adjusted threshold to target the most infectious people with COVID-19.

This suggestion is contrary to the recently updated testing guidelines of the White House Coronavirus Task Force.

Last Monday, the CDC changed its guidelines, which now say that if you’ve been exposed but don’t have symptoms, “you don’t necessarily need a test unless you’re a vulnerable person. Or that a doctor advises it.

Previously, the agency had recommended getting tested after any close contact with someone confirmed to be infected with COVID-19.

The Trump administration on Thursday announced it will purchase 150 million rapid tests, but doctors say testing process needs to be changed

The Trump administration on Thursday announced it will purchase 150 million rapid tests, but doctors say testing process needs to be changed

“The decision not to test asymptomatic people is really backwards. In fact, we should step up testing all different people, but we have to do it through completely different mechanisms, ”Dr. Michael Mina, epidemiologist at Harvard TH Chan School of Public Health, told The Times.

“We use one type of data for everything, and it’s just more or less – that’s it. We use this for clinical diagnostics, for public health, for political decision making, ”said Mina.

“It’s really irresponsible, I think, to give up on recognizing that this is a quantitative problem,” added Mina.

On Thursday, the Trump administration announced it would purchase 150 million rapid tests, but Mina says the testing process needs to be changed.

One solution to today’s testing might be to adjust the cycle threshold used now to decide if a patient is infected to a lower number.

Most tests put the limit at 40 or 37, which means you are positive for COVID-19 if the test takes up to 40 or 37 cycles to detect it.

The test’s threshold is so high that it detects people with the live virus and those with few genetic fragments that have remained from an infection and are no longer at risk, says Mina. It’s like finding a hair in a room after someone has left it.

Today, there are 5.9 million cases of COVID-19 in the United States and there have been more than 182,000 deaths

Today, there are 5.9 million cases of COVID-19 in the United States and there have been more than 182,000 deaths

Experts say a reasonable threshold for the virus would be 30 or 35 cycles, according to Juliet Morrison, a virologist at the University of California at Riverside.

Mina said he would set the threshold at 30.

New York State Laboratory Wadsworth analyzed cycle threshold values ​​in previously processed COVID-19 PCR tests and found in July that 794 positive tests were based on a 40 cycle cutoff.

With a threshold of 35, about half of these tests would no longer be considered positive. About 70% would no longer be considered positive if cycles were limited to 30.

In Massachusetts, 85 to 90 percent of people who tested positive in July with a cycle cutoff of 40 would have been considered negative if the cutoff was 30 cycles, Mina said.

“I would say that none of these people should be followed, not just one,” he said.

The Food and Drug Administration has said it does not specify the cycle threshold ranges used to determine who is positive and that “manufacturers and commercial labs set theirs.”

The Centers for Disease Control and Prevention said they were reviewing the use of cycle threshold metrics for “policy making.”

The CDC said its own calculations suggest it is extremely difficult to detect a virus living in a sample above a 33 cycle threshold.

On July 21, health workers register patients at a city-run COVID-19 testing center in New York City

On July 21, health workers check in patients at a city-run COVID-19 testing center in New York City

“It’s just a little mind-boggling to me that people aren’t recording CT values ​​from all of these tests – whether they’re just returning a positive or a negative,” said Angela Rasmussen, a virologist at Columbia University in New York. York.

“It would be useful information to know if someone is positive, if they have a high viral load or a low viral load,” she added.

The FDA has noted that people can have a low viral load when newly infected, and a test with less sensitivity would miss these infections.

Mina says these people can be tested again if they do.

People infected with COVID-19 are most contagious a day or two before symptoms appear about five days later.

Virology experts say there is a need now for tests that are quick, cheap, and abundant enough to frequently test anyone who needs them – even if that means the tests are less sensitive.

“It might not catch everyone who transmits, but it will definitely catch the most transmissible people, including super-spreaders. That alone would drive epidemics to practically zero, ”Mina said.

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