How Accurate Are Coronavirus Tests? - The New York Times

sisilihya.blogspot.com

Gov. Mike DeWine of Ohio received a negative coronavirus test result on Thursday, hours after a positive test result had stopped him from meeting with President Trump in Cleveland. The contradictory results during a high-profile moment underscored the challenges of testing, an issue that has repeatedly stymied the virus response in the United States.

“I’m sure the internet is lighting up with, ‘Well, you can’t believe any test,’” Mr. DeWine, a Republican, said during an interview with 92.3 WCOL, a Columbus radio station, on Friday.

“No one should take the results of this test and say, ‘Oh, none of these numbers are right,’” he added. “There is always a possibility for error.”

At issue are two types of coronavirus tests that are increasingly taking center stage as part of the virus response in the United States. As part of a screening by the White House, Mr. DeWine first received an antigen test, a newer type of test that provides faster results but is less accurate than traditional laboratory testing. He was later tested using a more standard procedure known as polymerase chain reaction, or P.C.R., an accurate but time-intensive method that requires samples to be processed at a laboratory.

Widespread, fast testing is the cornerstone of any virus response and an area where the United States has consistently fallen short. In order to ramp up testing to a level needed to stop the spread of the virus, experts are increasingly recommending a strategy that casts a wide net with widespread adoption of faster, less accurate tests. But that comes with drawbacks.

Latest Updates: The Coronavirus Outbreak

Updated 2020-08-07T21:07:20.816Z

• As the U.S. stimulus talks falter again, Trump’s advisers say they would tell him to act on his own.
• Cuomo says N.Y. schools can reopen in-person but leaves it up to districts to determine if, when and how.
• The U.S. economy added jobs last month, but only a small fraction of those lost in the spring.

See more updates

More live coverage: Markets

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

What is the difference between a P.C.R. test and an antigen test?

A P.C.R. test is the test that is probably most familiar to Americans. It involves taking a swab from a person’s nose and sending the sample to a laboratory to process.

The approach amplifies a sequence of nucleic acids in order to detect tiny amounts of the virus. Because the process amplifies the sequence, the test is highly accurate, but the results can take hours or days to process. “It allows you to get very high sensitivity, meaning most people who have the virus who have a P.C.R. test are going to get identified,” Dr. Miller said.

But there have been problems with access to the tests. As cases spiked, the demand overwhelmed laboratories, and shortages in the supply chain meant many Americans had to wait days — or even weeks — for results. The delays render the tests largely useless. Experts say results are needed within 24 to 48 hours to effectively quarantine and contact trace. In the United States, turnaround times are often stretching three to five days, or more.

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

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

How accurate are the results?

All virus tests have the possibility of an inaccurate result. “It is just a fact of clinical testing,” said 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 the traditional nasal swab, laboratory test. Interestingly, antigen tests are more likely to produce false negatives — missing someone who has the virus — than false positives, the opposite of what appears to have happened to Mr. DeWine.

The Coronavirus Outbreak ›

Frequently Asked Questions

Updated August 6, 2020

• Why are bars linked to outbreaks?

  • Think about a bar. Alcohol is flowing. It can be loud, but it’s definitely intimate, and you often need to lean in close to hear your friend. And strangers have way, way fewer reservations about coming up to people in a bar. That’s sort of the point of a bar. Feeling good and close to strangers. It’s no surprise, then, that bars have been linked to outbreaks in several states. Louisiana health officials have tied at least 100 coronavirus cases to bars in the Tigerland nightlife district in Baton Rouge. Minnesota has traced 328 recent cases to bars across the state. In Idaho, health officials shut down bars in Ada County after reporting clusters of infections among young adults who had visited several bars in downtown Boise. Governors in California, Texas and Arizona, where coronavirus cases are soaring, have ordered hundreds of newly reopened bars to shut down. Less than two weeks after Colorado’s bars reopened at limited capacity, Gov. Jared Polis ordered them to close.

• I have antibodies. Am I now immune?

  • As of right now, that seems likely, for at least several months. There have been frightening accounts of people suffering what seems to be a second bout of Covid-19. But experts say these patients may have a drawn-out course of infection, with the virus taking a slow toll weeks to months after initial exposure. People infected with the coronavirus typically produce immune molecules called antibodies, which are protective proteins made in response to an infection. These antibodies may last in the body only two to three months, which may seem worrisome, but that’s perfectly normal after an acute infection subsides, said Dr. Michael Mina, an immunologist at Harvard University. It may be possible to get the coronavirus again, but it’s highly unlikely that it would be possible in a short window of time from initial infection or make people sicker the second time.

• I’m a small-business owner. Can I get relief?

  • The stimulus bills enacted in March offer help for the millions of American small businesses. Those eligible for aid are businesses and nonprofit organizations with fewer than 500 workers, including sole proprietorships, independent contractors and freelancers. Some larger companies in some industries are also eligible. The help being offered, which is being managed by the Small Business Administration, includes the Paycheck Protection Program and the Economic Injury Disaster Loan program. But lots of folks have not yet seen payouts. Even those who have received help are confused: The rules are draconian, and some are stuck sitting on money they don’t know how to use. Many small-business owners are getting less than they expected or not hearing anything at all.

• What are my rights if I am worried about going back to work?

  • Employers have to provide a safe workplace with policies that protect everyone equally. And if one of your co-workers tests positive for the coronavirus, the C.D.C. has said that employers should tell their employees -- without giving you the sick employee’s name -- that they may have been exposed to the virus.

• What is school going to look like in September?

  • It is unlikely that many schools will return to a normal schedule this fall, requiring the grind of online learning, makeshift child care and stunted workdays to continue. California’s two largest public school districts — Los Angeles and San Diego — said on July 13, that instruction will be remote-only in the fall, citing concerns that surging coronavirus infections in their areas pose too dire a risk for students and teachers. Together, the two districts enroll some 825,000 students. They are the largest in the country so far to abandon plans for even a partial physical return to classrooms when they reopen in August. For other districts, the solution won’t be an all-or-nothing approach. Many systems, including the nation’s largest, New York City, are devising hybrid plans that involve spending some days in classrooms and other days online. There’s no national policy on this yet, so check with your municipal school system regularly to see what is happening in your community.

Mr. DeWine is expected to be tested again on Saturday.

States are increasingly turning to antigen tests as part of a strategy to ramp up testing. Mr. DeWine is part of a bipartisan group of governors — four Republicans and four Democrats — who are negotiating to purchase the tests from two medical companies, Becton, Dickinson & Company and the Quidel Corporation. The companies were the first to receive emergency authorization for antigen tests from the Food and Drug Administration, but the tests could produce false negative results between 15 and 20 percent of the time.

If the results are not always accurate, why are experts pushing for more rapid testing?

The United States is currently testing at a daily rate of 241 tests per 100,000 people, according to an estimate by Harvard Global Health Institute. By the same estimate, the country would 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 outbreaks as they occur.

To ramp up enough testing, experts say the United States cannot rely on traditional one-by-one laboratory tests alone.

Antigen tests offer one strategy that could prove useful for crowded settings like nursing homes or schools. “You have the advantage of being able to quickly identify people who might be infected and getting them isolated and separated,” Dr. Miller said. “Whereas where you have to wait 48 or 72 hours for a test result to come back, you have that window of time where people are often not fully isolated or quarantined.”

In short, there are societal benefits to casting a wide net with faster, less accurate tests, but it can cause confusion on a personal level, as the DeWine case seems to show.

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

But by Thursday evening, he had received better news.

“The antigen tests do give us a cheap way to do a lot of tests that are pretty good,” Dr. Miller said. “Pretty good is a lot better than none, and it collectively gets us a lot closer to the goal of being able to isolate and quarantine people when they need to be.”

Julie Bosman contributed reporting.

Let's block ads! (Why?)

"results" - Google News
August 08, 2020 at 03:54AM
https://ift.tt/3koQW68

How Accurate Are Coronavirus Tests? - The New York Times
"results" - Google News
https://ift.tt/2SvRPxx
https://ift.tt/2Wp5bNh

Bagikan Berita Ini