As the COVID-19 pandemic marches on, new, rapid tests offer hope for pumping the brakes on the virus’ spread.  The United States is falling far short in its testing efforts. More than 4 million tests per day would be needed to control the spread of the coronavirus, according to an analysis by Brown University and A healthcare professional adds the extraction reagent and a patient specimen to Abbott’s BinaxNOW COVID-19 Ag rapid test card, Sep. 2020.The right test for the job Experts say that the best test depends on the testing strategy.   “I think there’s definitely a time and a place for all of these tests, as long as they’re used properly,” said Wyllie. Currently, the CDC only recommends COVID-19 testing if people have symptoms or if they’ve been in close contact with an infected person. Because PCR picks up even tiny quantities of the virus it is much more sensitive than antigen testing. This means that PCR can more accurately diagnose COVID-19, particularly as the disease progresses and virus levels wane. “PCR is extremely sensitive. It can detect one molecule [of the virus],” said Michael Mina, epidemiology professor at Harvard University at a press conference. “I want to make it clear that PCR is a terrific tool. If I’m a diagnostic physician, I want to use PCR.”   However, because PCR tests are so sensitive, they may give a positive result when people are no longer contagious. “We’re actually missing people during the peak of their infection and we’re catching them too late,” said Mina.   Some experts say the best approach to tackling COVID-19 is frequent, widespread testing of asymptomatic people. Less-sensitive antigen tests may do the job because they perform well when virus levels are high and detect people when they’re most infectious. Best of all, these tests are cheap and quick. “If my goal is to use testing as a way to remove people who are infectious from the population, that’s where these rapid antigen tests really start to shine,” said Mina. According to Mina, the recent granting of an Emergency Use Authorization to a rapid antigen test is a step in the right direction. This type of simple, paper test could one day be available for use in homes. Although the FDA has not yet approved a home COVID-19 test, it recently provided recommendations for home testing standards, stating that these tests will be a “game changer in our fight against COVID-19.” “I really like the idea of a rapid test that you can do at home,” said Yale’s Wyllie. “This idea that we can get up in the morning and as we’re getting ready for work or whatever, taking a test.” But Wyllie says the success of this approach depends on test sensitivity and how often testing is done. “The problem with antigen tests at the moment is that I just don’t think they’re sensitive enough sometimes.”   Even with daily testing, a low sensitivity test could fail to identify the virus before a person becomes infectious. “In that 24 hours, they could go to a wedding, they could go to a funeral, they could go to a church choir. All these settings that we’re seeing become superspreading events.”How Superspreaders – People and Places – Drive the COVID-19 Pandemic A mix of biology, behavior and location is found to produce a majority of cases The limits of testing Experts agree that no test is perfect. Results depend on many factors such as the type of test, how the sample was collected and when the test was taken. “A negative [diagnostic] test doesn’t exclude the possibility that you will test positive tomorrow if you’re within that 14-day incubation period,” said UNC’s Weber. “I think testing is an important strategy but it’s not a substitute for physical distancing and mask wearing.” Steve Baragona contributed to this report.
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