Testing for COVID after the protests

I was referred on Twitter to this story from Twin Cities Pioneer Press, about COVID testing of people participating in the Minneapolis protests over the killing of George Floyd.

The headline is Early test results show few protesters caught COVID-19.  I think that’s a bit premature, though the story itself is fine and it makes sense to share whatever information there is about.

More than 3,300 people who participated in protests and community events after Floyd’s death were tested for the coronavirus …

Results from about 40 percent of the coronavirus tests done in St. Paul and Minneapolis this week show 1.4 percent of participants who were tested had contracted COVID-19. Health officials are awaiting the rest of the test results and are encouraging anyone who participated in mass gatherings to get tested — regardless of symptoms.

As a first reaction, it’s really good news that the health officials are trying to get everyone tested,  to mitigate any effects of the protest.  Because this is the internet, I probably also need to say that, yes, the protesters are imposing a infection risk on people who didn’t volunteer for it, but being killed by police is also a risk substantially imposed on people who don’t do anything to volunteer for it. And I should probably also say that this viewpoint may not be the policy of the University of Auckland (but it should be).

Getting back to the actual numbers, 1.4% seems quite a lot.  The story compares it to the 3.7% positive rate in current testing, but correctly points out that the usual testing is of people who are much more likely than average to have the virus.  Another possible comparison is that about 30,000 of Minnesota’s 5.6 million population have tested positive so far, or about 0.5%.   It’s easy to imagine that Minnesota has missed 2/3 of its cases (I could believe that NZ has missed 2/3 of its cases), so 1.4% isn’t looking so bad. On the other hand, that proportion in Minnesota as a whole is over the entire duration of the epidemic, not at one point in time.  And the 1.4% will, to some extent, be an underestimate of infections in those tested, since the accuracy of the test before you develop symptoms is not wonderful.  So, yes, 1.4% looks like some infections due to the protests.

Minnesota currently has about 4000 active COVID cases.  If (extrapolating wildly from the tests) there are 100 or so from the protests, and most of these people get diagnosed and are willing and able to isolate while infectious, the impact doesn’t really qualify as a ‘spike’.  If there hadn’t been proactive testing, most of these people would have had no reason to suspect they were carriers and a serious increase in cases would be more likely.