Washington (AFP)

Rapid test of new coronavirus designed by Abbott laboratories, touted by Donald Trump and used daily in the White House, produces between a third and a half of false negative results, according to a preliminary study carried out by university researchers from New York (NYU).

The test, which produced positive results in 5 minutes and negative results in 13 minutes, was compared to those of another slower machine. When the rapid test sample was diluted in a culture medium (a transport liquid), it missed a third of the samples confirmed positive by the other machine. This rate rose to 48% when the cotton swab remained dry, which is the method recommended by Abbott.

The researchers pre-published their comparison on the public site biorxiv.org, where thousands of researchers put their studies online while waiting for their review by a scientific journal.

The Langone medical center in NYU wanted to verify the accuracy of the new test because it would have greatly accelerated the screening of patients arriving in the emergency room and suspected of being infected with the new coronavirus Sars-Cov-2. Its advantage is that it is done on site, in a small machine called ID NOW, without the need to send the samples to a laboratory.

By comparison, the molecular test (PCR) of the pharmaceutical group Roche gives results in three and a half hours, and that of Cepheid 45 minutes. To detect the presence of the virus in a sample (taken from the nose, the back of the nose or the throat), these tests try to "photocopy" on a large scale the piece of virus that interests them, in order to make it visible.

It turns out that Abbott's test, according to this comparative study, is relatively reliable when it announces a positive result. But its effectiveness seems to decrease quickly when the amount of virus in the initial sample is reduced, which means that it misses many positive results.

This high rate of false negatives "makes this technology unacceptable in our clinical environment", conclude the authors.

On March 30, the American president himself presented Abbott's machine, which weighs about 3 kg and the size of a toaster, to the White House.

An Abbott spokesperson responded that the results were "not consistent" with other studies, and stated that "the rate of false negatives reported to Abbott was 0.02%", without further details . "It is not known if the samples were tested properly in this study," added the spokesperson.

© 2020 AFP