How much testing are we doing now? Nobody knows anymore.

I’m once again not providing my usual numbers section, since none of the trends in the numbers I’ve tracked have changed significantly, at least in their 7-day averages. But there are two numbers that deviated significantly from their overall trend yesterday: New cases jumped up to 48,000, after getting as low as 25,000 less than a week ago. So that’s bad. On the other hand, the test positivity rate for the US dropped to 5.0 yesterday. That’s good, since it was 5.3% two days previous.

So should we be concerned or optimistic? The problem is that we don’t actually know how many tests are being performed now. If tests are falling, then the fact that the test positivity rate is falling is still good news. But by the same token, if tests are falling the fact that new cases are rising is bad news, since it implies a greater percentage of people being tested are positive. But then how could the positivity rate be rising at the same time that tests are falling? This would imply that tests are rising, not falling.

However, the problem is that reported tests are falling. The Atlantic, which has produced perhaps the most insightful analysis of the pandemic, two days ago posted an article that led by noting that reported tests are down by about 100,000 a day recently. Does this mean that Trump is succeeding in his efforts to restrict testing?

Probably not. The fact is that it’s almost certain there’s a lot more testing going on than is being reported. The big unknown here is antigen tests, which were approved by the FDA in May and are cheap to produce; millions of these are now being manufactured every month. While they require a machine to evaluate them, they can be conducted in nursing homes, schools, workplaces and any other location where there’s a need for rapid tests. Yet only about 200,000 antigen tests have been reported nationwide since they were approved.

Why the discrepancy? The two main possibilities are that a) even though millions of tests have been distributed, only a small number of those have been used yet; or b) the schools, etc. aren’t reporting most results, for various reasons shown in the report.

It’s likely that b) is in fact the case, and most antigen tests just aren’t being reported. This might offhand seem to be good news, when combined with another fact: Antigen tests are less accurate than the standard PCR tests (which are almost all reported, of course). So any positive antigen test result needs to be confirmed with a PCR test. This is what happened with Ohio Gov. DeWine recently, who received a positive antigen test in the morning, but the PCR test that afternoon was negative. Of course, this means that nobody is likely to have to quarantine for 14 days because of a false positive test, which is good.

But the real problem is false negatives. While the FDA has some guidance that negative antigen test results should be confirmed, it’s highly unlikely they will be. So someone who might actually be sick – yet is asymptomatic – may move around and infect others. In other words, hospitalizations and deaths will be the only good way to track the spread of the virus. Of course, that means it’s no longer possible to prevent the spread in any meaningful way, or even to recognize if spread is increasing or decreasing. And that isn’t good at all.

 

I would love to hear any comments or questions you have on this post. Drop me an email at tom@tomalrich.com

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