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COVID-19’s “pool test” is promising and flawed



Washington (Associated Press)-Senior health officials in the United States are relying on a new method to greatly improve the screening of coronavirus in the United States: test samples are carried out in batches rather than individually.

Potential benefits include increased laboratory supplies, reduced costs, and expanded testing to millions of Americans who may unknowingly spread the virus. Health officials believe that asymptomatic infected persons are the main cause of more and more cases in more than half of the states.

Dr. Deborah Birx, the White House Coronavirus Response Coordinator, said at a recent laboratory expert meeting: “Pooling will enable us to perform from 500,000 tests per day to potentially 5 million per day Test”

;.

Currently, the federal health regulator has not approved any laboratory or test manufacturer to use the technology. The US Food and Drug Administration (FDA) issued a guide for testers in mid-June, hoping everyone would first show that mixing samples does not reduce accuracy, which is one of the potential shortcomings.

Therefore, it is unclear when aggregate testing can be conducted in schools and enterprises for large-scale screening.

The principle is simple: the laboratory does not combine a portion of each person’s nasal swab sample and then conduct the test instead of testing each person individually. A negative result will clear everyone in the batch. A positive result will require a separate retest of each sample. Pooling tests require hours of laboratory running tests to achieve the best results, rather than a single test used in a clinic or doctor’s office is much faster.

The idea of ​​the merger can be traced back to World War II, when it was thought to be able to quickly screen the blood samples of American conscripts for syphilis. Since then, it has been used to screen blood samples for HIV and hepatitis. Developing countries have used aggregated samples to expand test supply.

China reported that the method was part of a recent event that tested 11 million residents in Wuhan.

Darius Lakdawalla, a health economist at the University of Southern California, said: “Americans think this is a new concept because usually we don’t face the challenge of having to expand our testing capabilities.”

Lakdawalla and colleagues estimate that joint testing can save schools and businesses 50% to 70% of costs. Under their model, a group of 100 employees can be divided into 20 batches of five people. Assuming that 5% of people carry the virus, only five test results of the sample bank are positive and need to be tested separately. In the end, the merged method required 45 tests, and 100 tests alone.

But merging is not always the best option. Importantly, it does not save time or resources when used in COVID-19 hotspots (such as nursing home outbreaks). This is because the logistics and financial advantages of the pool will only accumulate when the test results of a few pools are positive.

Experts generally recommend using this technique when less than 10% of people are expected to test positive. According to an analysis by the Associated Press, about 7% of Americans tested positive for the virus in the past week, although the incidence rates vary widely. For example, the merger in Arizona will not be cost-effective. In Arizona, the surge of positive test results will exceed 22%. But this method may make sense in New Jersey, with a positive rate of less than 2%.

The State Health Laboratory of Nebraska began in March, and after obtaining special permission from the governor and FDA, batch testing was used. The person in charge of the laboratory said that due to the outbreak of the meat packaging plant, the positive rate rose to 17%, and they had to stop production a few weeks ago.

Dr. Peter Iwen said: “When these rates start to rise, we know that the merger will no longer work.”

A mixed test is reserved for large groups with low infection rates, which is related to the government’s increasing attention to people who have no symptoms of virus transmission, especially young people.

“This is a very good tool. It can be used in many situations, including in the community and even in the school.

Nonetheless, health officials may still have to convince some major players to adopt this method. LabCorp, one of the largest testing chains in the United States, said in an email that it is familiar with summary testing, but currently believes that “individual patient testing is the most effective way to screen for COVID-19.”

Dr. Colleen Kraft of Emory University is concerned that testing in batches (multiple rounds of screening for certain patients) may slow down the results of the test, which makes the infected person The key factor of isolation.

Kraft said: “If you want to do something quickly, you actually extend the turnaround time.”

She and others also worry about accuracy, because when screening in a larger population where the target disease is less common, the performance of the test tends to decrease.

Jennifer Nuzzo of Johns Hopkins University’s Covid-19 Test Insights Initiative said: “If we can’t believe the test results, then there is no need to test.”

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Follow Matthew Perrone on Twitter: @AP_FDAwriter

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Associated Press writers Lauran Nilgard of Washington, Nick Foster of New York and Christina Cassidy of Atlanta contributed to this report.

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




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