For the last weeks I was very convinced that mass testing would be one of the best ways to make reopening societies safer. This piece from Michael Hochman on statnews.com had me think about that. The idea is that frequent testing allows us to identify asymptomatic spreaders. But simply mass testing everyone regularly won’t solve the problem alone.
Even with testing every two weeks and a 24-hour lag in results, universal testing would catch less than half of asymptomatic carriers during their most infectious period.
On top of that, there are false negatives
Perhaps the biggest challenge is false negatives — tests signaling no infection in those who are indeed infected. Covid-19 testing is typically performed on samples from behind the nose or in the back of the mouth, and will be positive only if the sample happens to contain the virus. In some people, the virus may be present in high quantities only deep in the lungs. False negatives occur surprisingly often — perhaps as often as one-third of the time — which could lead to a false sense of security among those with such results.
and false positives
Testing those without symptoms can also lead to false alarms. PCR testing for the virus, which is the best way to identify an active infection, can detect the presence of SARS-CoV-2 — or remnants of it — for weeks, even when the infection is unlikely to be transmitted to others. Testing the entire population would undoubtedly identify a large number of such individuals, unnecessarily sidelining them from work and society.
My take-away is this: I think it still makes sense to test those most exposed as regularly as possible. Even if there are false positives, having some information is crucial. But probably it does not make sense to test everybody – especially not if these tests have to happen in person.