The President, the Virus, and the limits of Testing

I would hope everyone is praying for a swift recovery of the President. If there is one thing this country doesn’t need right now it’s more uncertainty and disruption thrown into the Election. As for commenting on the situation, I think it illustrates some vital points to understand about the virus that causes COVID19 and how our society needs to try to react to it. Of course, everything is a mine field given how emotional and split everyone is over politics. So I’m going to try to discuss in a somewhat neutral way a vital issue: the limits of testing. That does mean pointing out how the White House made a mistake about testing. Please don’t try to read between the lines on this with respect to my politics – there is no agenda here. Of course I have an opinion, and I think I’ve decided which one I’m going to vote against, but I’m not happy about it, and to be clear I don’t support either side.

I’ve ranted a lot about the problems with testing here in the US, and what is happening in the White House seems to be a classic case of the misapplication of a technique designed for one thing and using it for something else. The first thing you need to understand is how COVID acts in a person. The New York Times has a surprisingly good article on the progression of the disease today. I think their COVID coverage is still free. They have a lot of simple graphics that do a nice job of (literally) charting the disease; the key graphic is this, with the danger zone of 2-3 days marked:

From the New York Times: progression of COVID19.

The problem is that the kind of test used by the White House to test visitors, the Abbott ID Now system, is designed to determine if someone who has symptoms has COVID19 or something else. The advantage of this (vs. the more sensitive PCR test) is speed: you get an answer in 15 minutes vs. overnight at best. But … if you look at the graph, the time of peak viral load (the therefore infectiousness) is generally before the onset of symptoms. Worse, at that stage (between the first pink vertical line and the when the green “symptoms” line starts), the test has a 30% miss rate. So someone could have the virus – and be spreading it – and the Abbott test will miss it about 1 in 3 times. Let’s say you have 200 people in the inner circle. If it’s like the rest of the population in areas of community spread were in the 10-20% exposure range. Taking the low number, that’s 20 people. With a one in three miss rate on the daily tests, and the period of infectious but not symptomatic, you would statistically over a period of a couple months have three to five people wandering around for at least a day spreading the virus. That’s why other measures – masks, hygiene – are essential even with routine testing and temperature checks. No one measure is a silver bullet – but like layers of Kevlar in a bullet proof jacket, taken together they can beat this thing.

I suspect what happened is that the White House didn’t fully appreciate this. They were testing everyone on the staff, felt comfortable with that, and it probably wasn’t clear that this system wasn’t designed as a wide scale preventative measure. It was designed to test people who were already sick. Whose fault was that? Did the manufacturer oversell the product? Did that technical detail get lost in the rush to put something in place? Did they just ignore advice and engage in wishful thinking? All of the above (I’d put my bet here)? To be clear, this mistake isn’t limited to the White House – I know of at least one medical facility that has been doing the same thing (treating the rapid test as exclusionary rather than confirmatory), so they aren’t alone. The bottom line is that it was statistically pretty much inevitable that there was going to be an outbreak within the White House.

It is absolutely vital to realize that in the short to medium term there is no single solution for dealing with this virus. Testing is useful – but has limits. A vaccine will be useful – but will likely have significant limits. Masks are useful – but have limits. Shutdowns at one time could have been useful – but (IMNSHO) are no longer given the cost/benefits. Social Distancing is useful but has limits. Hygiene is always a good idea. Immunity may or may not be a thing. It is utterly insane that the US political system has decided that some of these are “Democrat” solutions, and some are “Republican” solutions.

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