Thread by @katherineefoley

A lot of people, myself included, have taken a #Covid_19 test before going to see a new group of family or friends. Practically, though, these tests can create a false sense of security bc of their high false negative rate. I'll explain in a thread: 1/x
qz.com/1905604/should…

2/x Some context: In the US, there are still some local testing shortages. But bc capitalism, private companies like @LabCorp, @everly_well, and @LetsGetChecked have started offering @US_FDA emergency-use authorized at home collection kits that get shipped off to a lab.

3/x These kits are ~$120 out of pocket, but insurance can cover them. It's a swab + PCR test, looking for SARS-CoV-2 genetic material. They typically return results in a couple of days, and you don't have to leave your home.

4/x The problem is, even at their best these tests have a pretty high false negative rate. Bc of #COVID19's long incubation period—median 4-5 days, sometimes 14—if you take a test too early after being exposed, it may not have had enough time to replicate in your body.

5/x This review from @JohnsHopkins looked at the false negative rate of #COVID19 tests and found that the first day of exposure, false negative is 100%; day 4 (probs no symptoms), it's 67%. Day 8, a bit after most people show symptoms, it's 20%. acpjournals.org/doi/10.7326/M2…

6/x In normal times, false negatives don't affect how medicine is practiced; if someone has flu-like symptoms but tests negative for the flu, you'd assume the test was wrong. If you're a doc, you treat accordingly. If you're a friend, you stay away until they're better.

7/x In #COVID19 times, we're using testing to try to identify asymptomatic/pre-symptomatic carriers, who we know exist. That's a new use for testing; usually it shows public health officials where outbreaks are happening.

8/x If you've known that you've been exposed to someone who has #COVID19 and get a negative test result, you should assume it's wrong, @Michael_Hochman from @KECKSchool_USC told me. You should isolate for 14 days, and assume that you're an asymptomatic carrier.

9/x That said, isolation is REALLY BAD for mental health. We need to see loved ones—so if you do, go ahead and take a test. But be mindful of your exposure levels before/after, the risks of those in the group, the activities you do—stay outside when you can, wear masks if you can

10/10 There are no 0 risk situations; you and your loved ones just have to decide for yourselves what risks you're okay taking on for yourselves and others. Sadly, I have no right answer for you—but some of the right questions to ask: qz.com/1905604/should…