Thursday, July 9, 2020

COVID-19 “pooled tests” show promise and pitfalls

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WASHINGTON (AP) – Canada’s top health officials are using a new approach to dramatically increase US coronavirus testing: combine test samples in batches instead of running them one by one.

Potential benefits include stretching laboratory supplies, cutting costs, and extending the tests to millions of other Americans who could unknowingly spread the virus. Health officials believe that infected people who do not have symptoms are largely responsible for the increase in the number of cases in more than half of the states.

“Pooling would give us the ability to go from half a million tests per day to potentially 5 million individuals tested per day,” said Dr. Deborah Birx, White House coronavirus response coordinator , at a recent meeting of laboratory experts.

So far, federal health regulators have not authorized any lab or test manufacturer to use this technique. The Food and Drug Administration released guidelines for test manufacturers in mid-June and wants everyone to show first that mixing the samples does not reduce accuracy, one of the potential drawbacks.

It is therefore unclear when pooled tests may be available for mass screenings in schools and businesses.

The principle is simple: instead of performing the test for each person individually, the laboratories would combine parts of samples of nasal swabs from several people and test them together. A negative result would wipe everyone out. A positive result would require that each sample be retested individually. Pooling works best with laboratory tests, which take hours – not the much faster individual tests used in clinics or doctors’ offices.

The idea of ​​pooling dates back to World War II, when it was considered for the rapid detection of syphilis in the blood samples of American recruits. Since then, it has been adopted to screen for blood samples for HIV and hepatitis. And developing countries have used pooled samples to stretch test supplies.

China said it used the approach in a recent campaign to test the 11 million people in Wuhan, the city where the virus first emerged late last year.

“Americans think it’s a new concept because normally we don’t have the challenge of having to stretch testing capacity,” said Darius Lakdawalla, health economist at the University of Southern California.

Lakdawalla and colleagues estimate that pooled testing could save schools and businesses between 50% and 70% on costs. Depending on their model, a group of 100 employees could be divided into 20 lots of five people. Assuming that 5% of people are carriers of the virus, only five pools would be positive, requiring individual tests. In the end, 45 tests would be necessary for the group approach, against 100 individual tests.

But pooling will not always be the best option. Above all, it will not save time or resources when used in COVID-19 hotspots, like an epidemic in a nursing home. Indeed, the logistical and financial advantages of pooling only add up when a small number of reserves is positive.

Experts generally recommend the technique when less than 10% of people should test positive. About 7% of US tests have been positive for the virus in the past week, according to an AP analysis, although rates vary widely from place to place. For example, the pooling would not be profitable in Arizona, where a surge pushed positive test results to more than 22%. But the approach could make sense in New Jersey, with a positivity rate of less than 2%.

The Nebraska State Health Laboratory used batch testing with special permission from the governor and the FDA starting in March. The director of the laboratory said that they had to stop several weeks ago when their positive rate increased to 17% with epidemics in meat packing factories.

“We knew that pooling no longer worked when these rates started to rise,” said Dr. Peter Iwen.

The pooling of pooled tests for large groups with low infection rates is consistent with the government’s growing focus on people with no symptoms spreading the virus, especially the youngest.

“It is a very good tool. It can be used in all kinds of circumstances, including at the community level or even in schools, “said Dr. Anthony Fauci, the country’s leading infectious disease specialist, on Tuesday.

However, health officials may need to convince some key players to adopt the method. LabCorp, one of the largest test chains in the country, said in an email that it is familiar with pooled testing, but currently believes that “individual patient testing is the most effective and efficient way To screen for COVID-19.

Dr. Colleen Kraft of Emory University is concerned that batch testing – with its multiple screening cycles for some patients – may slow test results, a key factor in quarantining infected people.

“If you try to do something quick, it actually extends the turnaround time,” said Kraft.

She and others also have concerns about accuracy, as test performance tends to decrease when screened in larger groups of people where the targeted disease is less common.

“If we can’t trust the test results, there’s no point in doing it,” said Jennifer Nuzzo, of the Covid-19 Testing Insights Initiative at Johns Hopkins University.


Follow Matthew Perrone on Twitter: @AP_FDAwriter


Writers AP Lauran Neergaard in Washington, Nicky Forster in New York and Christina A. Cassidy in Atlanta contributed to this report.


The Associated Press Department of Health and Science is supported by the Department of Science Education at the Howard Hughes Medical Institute. The AP is solely responsible for all content.


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