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How accurate are virus tests? The results of Gov DeWine show positives and negatives

Ohio Gov. Mike Devine received a negative test for coronavirus on Thursday, hours after a positive test stopped him from meeting with President Trump in Cleveland. The conflicting results highlighted the challenges of the tests at an important time, a problem that has repeatedly hampered the virus’s response in the United States.

“I’m sure the Internet is lit up with ‘Well, you can’t believe any of the tests,'” Mr. Dewin, a Republican, said in an interview with 92.3 WCOL, Columbus Radio, on Friday.

“No one should take the results of this test and say, ̵

6;Oh, none of these numbers are accurate,'” he added. “There is always the possibility of error.”

Two types of coronavirus tests are controversial, which are increasingly at the center of the virus in the United States. As part of the White House screening, Mr. DeWine first received an antigen test, a newer type of test that gives faster results but is less accurate than traditional laboratory tests. It was later tested using a more standard procedure known as polymerase chain reaction or PCR, an accurate but time-intensive method that requires samples to be processed in a laboratory.

Widespread, rapid tests are the cornerstone of any virus response and an area in which the United States is constantly lagging behind. To increase testing to the level needed to stop the virus from spreading, experts are increasingly recommending a strategy that throws a wide network with the widespread application of faster, less accurate tests. But this comes with drawbacks.

To better understand the difference between the two types of tests and the accuracy of the tests in general, we spoke with Dr. Bill Miller, an epidemiologist at Ohio State University.

The PCR test is the test that is probably best known to Americans. It involves taking a swab from a person’s nose and sending the sample to a laboratory for processing.

The approach enhances the nucleic acid sequence to detect small amounts of the virus. As the process enhances consistency, the test is very accurate, but it can take hours or days to process the results. “This allows you to get a very high sensitivity, which means that most people who have the virus who have a PCR test will be identified,” said Dr. Miller.

But there were problems with access to the tests. As cases increased, demand overwhelmed laboratories, and a shortage of supply chain meant that many Americans had to wait days – or even weeks – for results. Delays make tests largely useless. According to experts, the results are needed within 24 to 48 hours for effective quarantine and contact tracking. In the United States, lead times often extend from three to five days or more.

Antigen tests look for a protein that is part of the virus. They can also be done with a nasal swab, but can provide faster, easier-to-decipher results, similar to a pregnancy test.

Antigen tests can give results in less than an hour. But because the process does not amplify the particles, Dr. Miller said “the ability to detect the virus is lower by definition.”

All virus tests have the possibility of an inaccurate result. “This is just a fact of clinical trials,” says Dr. Miller, who recommended using common sense about the risk of exposure when evaluating unexpected results.

But antigen tests are generally less sensitive and less accurate than a traditional nasal swab, a laboratory test. Interestingly, antigen tests are more likely to generate false negatives – missing someone who has the virus – than false positives, the opposite of what seems to have happened to Mr. DeWine.

Mr DeWine is expected to be tested again on Saturday.

Countries are increasingly turning to antigen testing as part of a strategy to increase testing. Mr. DeWine is part of a bipartisan group of governors – four Republicans and four Democrats – who are negotiating to buy the tests from two medical companies, Becton, Dickinson & Company and Quidel Corporation. The companies were the first to receive emergency approval for antigen tests from the Food and Drug Administration, but the tests can lead to false negative results between 15 and 20 percent of the time.

The United States currently tests 241 tests per 100,000 people daily, according to an estimate by the Harvard Global Health Institute. According to the same estimate, the country will need 355 tests per 100,000 people to slow the spread of the virus and more than 1,000 tests per 100,000 people to truly suppress the virus by detecting and responding to epidemics as they occur.

To increase enough testing, experts say the United States cannot rely solely on traditional laboratory tests.

Antigen testing suggests a strategy that could be useful for overcrowded conditions such as nursing homes or schools. “You have the advantage of being able to quickly identify people who may be infected and isolate and isolate them,” Dr. Miller said. “Whereas where you have to wait 48 or 72 hours for the test results to return, you have this period of time in which people are often not completely isolated or quarantined.”

In short, there are public benefits to throwing a wide network with faster, less accurate tests, but this can lead to personal confusion, as is the case with DeWine.

Speaking from his home in Cedarville, Ohio, on Friday, Mr DeWine said it was “quite a shock” to say he tested positive. He recalled that after receiving the news, he and his wife Fran returned home. “Fran fixed me some chicken and rice soup,” he said. “She thought we had settled here for a long time.”

But by Thursday night, he had received better news.

“Antigen tests give us a cheap way to do a lot of tests, which are pretty good,” Dr. Miller said. “A good person is much better than no one and collectively brings us very close to the goal of being able to isolate and quarantine people when they need to be.”

Julie Bosman contribute to reporting.

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