Baseball, football, soccer basketball, golf, and for all I know tiddledywinks are planning to reopen, but not before testing their athletes daily for the Coronavirus. As I mentioned here earlier this month, the New England Journal of Medicine reported that the sensitivity of the tests for the virus is no better than 70%.
Our “experts” in this field seem determined to ignore the issue of false positive tests for COVID-19. Nevertheless, a test that is only 70% sensitive will give a false positive test in 30% of any test group; ie, 30% of the group that doesn’t have the virus will test positive
When we test a group (athletes) which consists of the healthiest specimens on earth – well maybe not the golfers and tiddliwinks players – and do so daily with low sensitivity tests, they’ll all eventually test positive. Consider the 3,748 Tyson employees tested in Benton and Washington Counties (AR), 481 were found to test positive for the coronavirus, with 455 of those patients reporting no symptoms. You only need half a brain, which our experts seem to have misplaced, to realize that a lot of these positive tests are false positives.
You can be pretty sure that our current plan to reopen sports will fail as a succession of athletes test positive for the Coronavirus, as has already started to happen. Ignorance can triumph over anything but Father Time. If we test often and long enough, all the athletes will eventually test positive.
As I’ve repeatedly said here, a positive test can be either a true or false positive test. Similarly, a negative test can be either true or false. We seem determined to ignore this inescapable characteristic of testing. Not only must the sensitivity and specificity of a test be known, but an estimate of the prevalence of the disease (the percent of patients with the virus) in the tested population must be available pre-test to adequately assess the likely ratio of true to false test results. Everything else being equal, the higher the prevalence of the virus the more likely a positive test will be a true positive. But the reverse is true for a negative test. The higher the prevalence the more likely a negative test will be a false negative. If you don’t wish to grapple with Bayes’ Theorem, you’ll have to take my word about these facts of testing.
Alas, our testing regime is as incoherent as is our economic policy. Immediately below in italics are the four recommendations from the NEJM paper mentioned above. You should be able to understand why sports are unlikely to return any time soon. The tests are not good enough and the information needed for their accurate interpretation is unavailable.
First, diagnostic testing will help in safely opening the country, but only if the tests are highly sensitive and validated under realistic conditions against a clinically meaningful reference standard.
Second, the FDA should ensure that manufacturers provide details of tests’ clinical sensitivity and specificity at the time of market authorization; tests without such information will have less relevance to patient care.
Third, measuring test sensitivity in asymptomatic people is an urgent priority. It will also be important to develop methods (e.g.,prediction rules) for estimating the pretest probability of infection (for asymptomatic and symptomatic people) to allow calculation of post-test probabilities after positive or negative results.
Fourth, negative results even on a highly sensitive test cannot rule out infection if the pretest probability is high, so clinicians should not trust unexpected negative results (i.e., assume a negative result is a “false negative” in a person with typical symptoms and known exposure). It’s possible that performing several simultaneous or repeated tests could overcome an individual test’s limited sensitivity; however, such strategies need validation.