Proposed COVID-19 test strategy faces pitfalls

If someone takes the COVID-19 test, the result will do one thing. Tell the person if the coronavirus is in the body. However, some researchers are trying to do more with their tests and, as a result, are reconfiguring their goals. Instead of just finding someone Infected In case of viruses they Contagious And there is a risk of spreading it to others.

This proposal is Pandemic Under control In the United States. This will enable isolation and a more targeted approach to isolation, which will give a better understanding of when people are most at risk to others.

The way you think about testing will change significantly. Clinicians have never used tests for respiratory infections like COVID-19 to determine if anyone is infected, says Matt Binnicker, dean of clinical virology at the Mayo Clinic in Minnesota. Says. He says the concept is interesting and could be useful. “But there are many potential pitfalls.”

Now let’s think about testing. When researchers develop tests for viruses, they usually aim to make them as accurate as possible. The Food and Drug Administration grades tests based on how well they can catch everyone who is infected and how often they exclude everyone who isn’t. The best test is usually the one that can detect anyone who has any virus in their system.

But the problem with coronavirus is that it gets attached. Only a small amount of the genetic material of a virus can stay in someone’s nose or throat, even after it has improved. This may keep your test positive for viruses. That’s one reason for the expert think Very sensitive tests have their downsides. These tests often catch people who do not need to be isolated because they are already experiencing a course of illness.

The alternative is to use a less sensitive test. This is an idea promoted by experts like Michael Mina, an epidemiologist at Harvard School of Public Health, New York Times And Atlantic.. These tests are unlikely to return positive if the patient sample had only a few bits of the virus. Instead, a large amount of the virus floating in the body can be a sign that an active infection is at risk even if no symptoms are present. Some experts say that is desirable, as public health authorities are the people who are most concerned.

There are several ways to do that. First, it relies more on tests to detect small proteins on the surface of coronaviruses. These antigen tests are fast, but tend to be less accurate. You can also change how information from more commonly used and more accurate PCR tests is interpreted. PCR tests look for coronavirus genes. They make a copy of the virus in the sample and repeatedly amplify it until it becomes detectable. The higher the number of copies needed to detect a virus, the less abundant it is. To increase the likelihood that your test will flag samples that can ignore viruses, Clinician can lower cut-off point The number of copies that have passed through the sample.

However, these “test people with insensitive tests” strategies are hypothetical. The idea is that people with a lot of viruses are highly contagious, and people with low levels of the virus are less contagious. It’s not an unreasonable assumption, says Mark Srifka, a professor at the University of Health Sciences of Oregon who studies viral immunology. This is intuitive. People with more viruses are more likely to exhale droplets of the virus than people with less viruses.

There is some indirect evidence to support this idea. In the experiment it was Easy to grow Coronavirus From patient samples with higher viral load than samples with lower viral load. This indicates that a higher number of samples of the virus are actually infected (not just dead remnants). Difficult to find infectious virus in collected samples About 10 days According to Slifka, after the symptom has started, it’s the window, and contact tracking shows that the virus is most likely infected.

But still not enough data to fully explain Relationship between virus level and infectivity.. People with low levels of the virus are less likely to infect others, but they are not immune. “I don’t think there is enough data to conclude that people are only infectious if they get a really large amount of virus,” says Binnicker. “I’m pretty comfortable saying people are More Contagious. ”

That is because the level of virus is not the only one that can contribute to infectivity. People who have a lot of virus but no symptoms may be less likely to infect others than people who cough more often because of low levels of the virus. “It’s not all talking,” says Jen Hemstra, associate professor of chemistry at Emory University.

The virus levels measured by the tests are also sometimes wrong. Someone may have a higher level of virus than what appears on a swab. It depends on how exhaustive the test is. If the tester only lightly rubs a cotton swab into his throat, he may not pick up the virus much, even if the person is actually at a high level. A low sensitivity test may not be flagged when there should be enough virus. “We’ve all done throat-touch streptococcal tests, and some can actually affect the test with a nurse who scrapes it,” says Binnicker.

If you reduce the sensitivity of your test, you also risk missing out on people in the early stages of infection. The amount of virus begins to drop, rising rapidly at the onset of the disease and then falling. The test does not distinguish between those who have a low viral level because they are recovering and those who are ill but have a low viral level. Newly ill people soon become infected with high levels of the virus (and can become more contagious).

Slovak features a fictitious person named Bob who comes into contact with someone with COVID-19. When tested, Bob has a low level of virus. “He may be downhill, has already cleared it, and is not likely to be contagious,” Slifka says. “Or, conversely, the viral load may be low and then rise.”

This is a fixable issue, but to get more tests, you need to get more information from Bob and submit Bob. That way, if he can’t be flagged for a test on Monday, he’ll be tested again on Wednesday to see if his viral level has risen. “If we can test people often enough and combine that with a lot of monitoring and data collection, we can really start connecting,” says Heemstra.

Implementing this strategy means dramatically expanding the amount of testing done every day in the United States and keeping people from waiting Multiple days To get results. It requires increased manufacturing, better distribution, and political will, as the Trump administration seems to have decided to limit testing. Government to Center for Disease Control and Prevention Change guidelines When a person without symptoms should be examined. U.S. test leader Admiral Brett Guilloire said this week that a world where all Americans can test COVID-19 on a regular, inexpensive, and fast basis. Unrealistic “Utopia world”.

Aside from the logical issues, Binnicker says he would like to see more evidence that insensitivity testing actually distinguishes infected from infected and helps control the spread of COVID-19. This can mean testing hundreds of people several times a week with low sensitivity tests and repeating the tests to see if they can prevent the spread of the virus.

“Talking about innovative ideas is always helpful,” he says. “I think the problem is that it was presented without much supporting data to show that the proposition works.”