Coming Down from the Plateau

The covid pandemic has plateaued in the US, but the lockdown that’s slowed the spread will soon be relaxed. What’s to keep contations from spiking again? Maybe even more importantly, what would it take to come down the other side of the plateau? The accepted answer: widespread testing, quarantining, social contact tracing.

Those who test positive get quarantined, and in many locales their social contacts get traced. However, diagnostic tests are administered primarily to those who’ve become very ill, which means they’ve already been infected and contagious for a week or more. And nine of ten infected experience few or no symptoms, so they never get tested, all the while being fully capable of transmitting the virus to others.

How do you identify, isolate, and track social contacts of the untested and the asymptomatic? More testing: that’s the usual answer. But who should get tested? The US tests 150K seriously symptomatic people per day, of whom around 20% test positive — that’s 30K new diagnoses per day. Meanwhile the actual new case count is ten times that, or 300K per day. Even if ten times as many daily tests are administered, it’s just a crap shoot if you’re trying to find the asymptomatic and presymptomatic cases.

Suppose the country were to focus its case-tracking program exclusively on individuals presently experiencing symptoms, at all levels of severity. That would limit potential impact, at least initially, to maybe half of those who are infected and contagious. Individuals’ symptoms can be monitored, continually and inexpensively and rapidly, with self-report apps and infrared temperature checks. Expand lab testing to 750K per day — five times current capacity — and those symptomatic from corona can be identified and quarantined. That would prove a challenge, technologically and logistically and financially, but it’s probably within reach.

Next comes contact tracing. Yes, there are apps based on GPS proximity of mobile phones to each other, but let’s assume personal phone contact is the preferred tracing strategy. Ignore the random brief encounters in the shop or at the park: tell me about those with whom you’ve shared personal space for at least ten minutes during the past week. One of those contacts is the likely source of your infection; the rest probably weren’t infected, at least not yet. I’ll track those people down and test them, regardless of whether or not they feel ill or are running a fever. Assume an average of 7 close extended recent social contacts for each newly diagnosed case — this approach would require another sevenfold expansion of testing capacity. But if it’s successful, tracing can work back upstream, capturing an increasing percentage of the asymptomatic carriers of the disease and further reducing contagion.

Here’s a potentially viable program for bringing the contagion rate low enough not just to flatten the wave but to extinguish it altogether. Maybe 50 to 100 thousand FTEs would be needed to do the job thoroughly: that can achieved by hiring and training a small fraction of those who have lost their jobs due to the pandemic shutdown. And maybe 150K x 5 x7 = 5 million diagnostic tests per day would need to be performed, with results being obtained not in days but in hours in order to keep up with the virus.

This vast extension of testing capacity, it’s widely agreed, is the bottleneck. Suppose testing can’t be ramped up fast enough — are there alternatives?

Let’s say that the contact tracer gets in touch with someone who’s had recent close contact with a newly diagnosed case, but who isn’t experiencing symptoms. The tracer can encourage this social contact to self-isolate for two weeks, just in case. It might be difficult for this person to collect two weeks’ paid sick leave without feeling sick. Can the contact tracer “write a note to the boss” — an official notification that can be presented to the contact’s employer? Maybe, but it’s likely to require quarantining tens of millions of Americans at any given time, most of whom aren’t even infected. Probably not feasible.

What about more intensified social distancing of social contacts that doesn’t go all the way into quarantine? Avoid extended physical proximity with others. Wear a mask whenever social distancing can’t be maintained. We’ll check in with you daily to see how it’s going. If you start experiencing symptoms, we’ll get you tested. Granted, this is the preventive armamentarium that’s already widely recommended to all. But if you know that you’ve been in recent close contact with someone who’s tested covid-positive, wouldn’t you be more motivated to adhere to the protocol, protecting both yourself and others? And might not the ongoing support and encouragement of a health professional keep you on track during your two-week stint of relative self-isolation?

 

 

2 thoughts on “Coming Down from the Plateau

  1. Here’s an article showing how many case trackers each state currently has available, as well as how much they intend to increase staffing. Not adequate, but not as bad as I’d feared. Lots of between-state variation — my present home state of North Carolina is decidedly understaffed and unprepared.

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  2. From this article:

    President Donald Trump said he thinks the U.S. will “very soon” be able to test 5 million people a day for the coronavirus – but there’s “no way on Earth” the country can reach that goal, according to the government’s top testing official.

    “There is absolutely no way on Earth, on this planet or any other planet, that we can do 20 million tests a day, or even five million tests a day,” Adm. Brett Giroir, assistant secretary of health who is in charge of the government’s testing response, told TIME in an interview he gave Tuesday morning that was published later in the evening. The interview took place before Trump’s remarks about testing.

    The U.S. will be able to test 8 million per month by May, Giroir told Time.

    So that supports Plan B for contact tracing; i.e., the scheme outlined in the last paragraph of this post. Well, no it won’t. Per the post, this approach would need about 750K tests per day, starting ASAP: that’s 22 million tests per month, or 3 times next month’s boosted capacity.

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