Minnesota’s Covid-19 tracing regime is being overwhelmed

On April 13th, in the depths of Minnesota’s shutdown, Gov. Walz explained what it would take for him to allow the economy to reopen:

Minnesota Gov. Tim Walz threw down a gauntlet Monday on when the state can restart the economy he shut down last month to gird against the spreading coronavirus pandemic:

5,000 tests per day.

And a robust ability to trace infections and isolate those carrying the virus.

It’s an ambitious standard — one he likened to the quest to put a human on the moon — and it’s not clear how soon it can be achieved.

The state has smashed this first target. For the seven days up to and including May 13th, Minnesota reported an average of over 5,000 tests daily for the first time. It is now running at more than ten times that, an average of upwards of 50,000 tests a day.

But on the latter target, Minnesota is failing.

Data from the Department of Health’s Weekly Covid-19 Report for November 19th – the most recent – shown in Figure 1 tells us the percentage of cases which have been traced to various sources since the start of the pandemic. We see that 38.8% of cases are ‘Unk./Missing’. We also see that a further 19.5% are listed as ‘Community (no known contact)’, which the Department of Health defines as:

Case has no known exposure to a positive case and does not fit into any of the previous categories.

In other words, we have no idea where 58.3% of Minnesota’s diagnosed cases of Covid-19 were exposed. Our state’s system for tracing infections has traced about four out of ten.

Figure 1: Share of Covid-19 cases by likely exposure, to November 12th

Source: Department of Health

As cases have mounted recently, this has only got worse.

Minnesota’s second surge in cases began in mid-September. Looking at the Weekly Covid-19 Reports for September 17th and November 19th, we can see where the new cases in this second surge have been traced to. Of the 163,184 new cases diagnosed over that period, 67.1% are categorized as either ‘Unk./Missing’ or ‘Community (no known contact)’. In short, we have no idea where 7 out of 10 new cases in this second surge were exposed.

Figure 2: Share of Covid-19 cases by likely exposure, September 17th to November 19th

Source: Department of Health

This is not to criticize the tracers. Rather, it is to note that they are doing an impossible job. The sheer number of cases is overwhelming them, as it was always likely to. Back in May I wrote that:

…state officials suggest that something like 513,600 Minnesotans have been or are infected with Covid-19. Even if it is half that, 256,800, can we identify all of them? If we do, can we trace all their contacts? If we can, can we quarantine them all? To ask the question is to answer it. Quite simply, if the state officials are right about a case-to-infections ratio of 1%, Gov. Walz is not going to be able to test, trace, and isolate.

Test, trace, and isolate might have been a very sensible strategy when infections were few in number, but if state officials are correct that horse has bolted. 

That is exactly what we are seeing now. What it means is that we ought not to make tracing a particular metric of how well or badly the state government is handling this. To do so, to set an unattainable goal, is to guarantee failure. We should only pick goals we have a chance of achieving.

John Phelan is an economist at the Center of the American Experiment.