Pooled testing could help schools reopen
We need not only more tests but also efficiency
Imagine if the school year starts and a child develops a fever at school. They are referred to their doctor to get tested, but the results take one week. What is the school to do while it waits? Classroom and building closures could be widespread, and in many cases the child will turn out not to have COVID-19. In other cases, delays could lead to school outbreaks.
These scenarios can be avoided with adequate testing resources, but news reports suggest that the widespread outbreaks occurring in many states have outpaced our growth in testing, leading to long delays in getting results.
Although we need to increase the supply of tests, we should also consider ways to stretch the existing supply by using tests more efficiently. Pooled testing, in which samples from multiple people are tested together, is one such solution.
Schools, often underfunded and lacking necessary supplies in the best of times, could particularly benefit from this increased efficiency.
In pooled testing, samples of multiple people (usually four) are mixed together and tested as one. If the test is negative, all four are assumed uninfected. If the test is positive, each individual in the pool is retested separately to identify the infected persons.
Recently, researchers in Nebraska piloted this approach and found that they could reduce the number of COVID-19 tests needed by 69%. Subsequent teams refined the method, and the Food and Drug Administration has approved pooling of a test created by Quest Diagnostics.
Fewer tests needed
The main criticism of pooled testing is that it can substantially reduce the number of tests used only when the positive rate is below 5%. Once it crosses that threshold, too many of the pooled tests come back positive, increasing the number of tests needed. In many states with COVID-19 outbreaks, the positive rate far exceeds 5%.
Recent research suggests that pooled testing can help at higher positive rates, if infected people are not randomly dispersed throughout the population but grouped and tested together. For example, if everyone in a classroom is exposed, school protocol may require them to be tested together. If more than one of them is infected, infected samples will likely be contained in the same pool. By including many of the infected people in only a few pooled samples, the amount of secondary testing is reduced.
The research suggests that when grouping like this exists, pooled testing significantly reduces the number of tests used when the positive rate is as high as 13%. This greater threshold would allow for rollout of pooled testing in areas now thought to have too high a positive rate, which would reduce test wait times, stress over test results and unnecessary quarantine.
States can examine series of tests and determine how much infected persons group together in the population and determine whether pooled testing is appropriate.
Pandemic could worsen
Although we have dramatically increased the number of tests performed each day — up to about 1.74 million as of July 21 — the pandemic has continued to spread, and the number of cases has outpaced our ability to test.
If we do not increase testing rapidly enough, we will lose ground to the pandemic and further hinder school reopening plans. The problem will likely worsen as students go back to school because they and their families who were isolating at home might be exposed at levels they were not before. We need some combination of increased test supplies or more efficient tests to address this problem.
No single approach will suddenly make the test capacity sufficient to contain the pandemic. Efforts across industry to make additional tests, research to improve the efficiency of those tests, policies that facilitate delivering tests, and the public’s perception of the cost and benefit of the test will all play a role.
As the nation continues its push to return to normal routines with school and work, as many other countries have done, pooled testing may be key in helping us get there.