Pooled Covid-19 testing could help reopen schools safely
November 27 2020 11:59 PM
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Vaccine or no, testing and tracing Covid-19 infections will be crucial to returning America fully to work and school. It’s a key area where the Trump administration has let the country down, and something that President-elect Joe Biden has vowed to fix with a major surge of new testing capacity.
But even many countries that have committed to an aggressive testing regime are finding it extremely expensive and time-consuming. In response, some have relied on a method that isn’t much talked about in the United States, though it’s well understood: Pooling the lab samples of several people at once. With new evidence showing its effectiveness — as well as potential weaknesses if it isn’t done correctly — pooling is something the Biden administration should seriously explore, especially as a way of reopening schools once the current surge subsides.
Pooling samples is exactly what it sounds like. Sometimes it involves using the samples from nasal and throat swabs, or in its simpler form, collecting saliva in cups and mixing it, usually from five people at a time, sometimes more. If the test comes up negative, all the people are considered clear of infection. If not, everyone in the group is retested individually. It can dramatically cut down the number of tests that need to be performed, which means far less cost and less straining of capacity.
Some private schools, such as Duke University, have been using it in the United States and have stayed open without outbreaks. On a much larger scale, China used it to test almost the entire population of Wuhan, where the virus was first identified in December. That’s 11mn people.
A recent study demonstrated that, for Covid-19 pool testing, a test could evaluate pools of at least 32 nasal samples without losing sensitivity, or the ability to correctly identify true positives.
But US health officials generally have been talking about pools of lower numbers. Generally speaking, the greater the disease’s prevalence in a population, the smaller your pools have to be.
Yet pooled testing has been rare in the United States. In part, that’s for good reason: The testing is effective only when infection rates are low — because that means less chance of needing to retest each person in a group — and for the most part, we’re falling short.
The tests can be highly accurate, but that depends on how the testing is done and how many people are in each pool. Overloading the pools would yield too many false negative results, because multiple clean samples in the pool can dilute an infected one below the test’s ability to detect the virus.
Still, this is an especially promising avenue for schools, where infection rates appear to have stayed on the low side, compared with the general population. By bringing down costs, students could be tested more often, making everyone feel safer about reopening campuses. We’re still hoping not to lose the entire academic year. – Tribune News Service



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