The bottom line is that the more often you use the tests, the better, said Dr. Michael Mina, an epidemiologist at Harvard and a proponent of rapid testing. (Dr. Mina advises Detect, Inc., a diagnostics company working on a rapid molecular test.) If you want to spend time with a medically vulnerable person, you should take a test a few days before seeing them, and then take another test on the day of the visit. “Think about, How do I test as close as possible to the thing that I’m doing?” Dr. Mina said. “When I go visit my parents, I always bring rapid tests with me. Right before I walk in the door, I use the test in my car.”
What do I do if the test is positive?
Most of the time, a positive result means you have the coronavirus, particularly if you have symptoms. But false positives do happen. Recently, Ellume, an Australian company, recalled nearly 200,000 test kits because of concerns about a higher-than-expected rate of false positives.
If there’s reason to doubt a positive result, take another test, preferably from a different manufacturer or at a testing center. People hosting large events, like weddings, and using the tests to screen guests should have a few extra tests on hand from a different brand for those guests who test positive. You can be confident in the result if the second test is negative, Dr. Mina said.
“It would be really rare for someone to have a true positive and then have a second test show a false negative result,” he said. “If you’re having a dinner, you may as well just cancel dinner if someone tests positive. But if it’s a high consequence event, like you’re having a wedding and flying somewhere, and you’re going to screen a few hundred people, you may get a false positive and want to test again.”
How do I find a home test?
Although supplies are expected to improve in the coming weeks, the tests can be difficult to find right now. Try the websites of stores like CVS, Walgreens, Costco or Walmart or check with a local drugstore. I recently searched the CVS website for a friend in New Jersey and found BinaxNow tests at a store about 30 minutes away. When he arrived, he found the shelves stacked with tests.
A word of warning: Make sure you search by brand name. If a store is sold out of a rapid test, the website may direct you to a different type of test, called a home collection test, that requires you to mail the sample to get the result. But hold out until you find a rapid test. “The fact that they are rapid,” Dr. Gronvall, of Johns Hopkins, said, is what “makes them a really great test to make sure somebody is not infectious at that moment.”