What Does ‘Negative’ on a Coronavirus Test Really Mean?

The BinaxNOW has emergency clearance from the F.D.A., however solely when administered within seven days after the onset of symptoms. Researchers don’t but know the way the take a look at will carry out in individuals exterior this window. Mr. Trump acquired a number of of those exams throughout his second week of sickness, all of which returned unfavorable outcomes.

“The tests have to be used when they’re supposed to be used,” stated Andrea Prinzi, a medical microbiologist on the University of Colorado, Anschutz. “That’s when they’re going to help you the most.”

Both P.C.R. and antigen exams have one other limitation: They search for hunks of the virus’s anatomy — particles from the pathogen — and can’t decide whether or not the virus continues to be energetic. Some individuals who have been contaminated by the coronavirus could register as P.C.R. constructive for weeks, even months, after they’re not contagious or unwell, just because exams are choosing up on innocent souvenirs of an an infection gone.

“Neither is a measure of actual, live virus,” Dr. Garner stated, of P.C.R. and antigen exams.

That’s the place viral tradition is available in. Scientists can take a pattern from a particular person’s airway after which attempt to coax the coronavirus into infecting cells in a lab. But these procedures should not extensively obtainable to the general public, as a result of they should be carried out in a high-containment facility by individuals particularly educated to work with lethal pathogens.

These restrictions have led a number of scientists to experiment with P.C.R.-based exams that search particularly for subgenomic RNA as a possible proxy for active virus. Subgenomic RNA is a sort of genetic materials that’s produced solely after the coronavirus has contaminated a human cell. The compound can thus act as a form of molecular beacon that may alert researchers to a virus that has began to breed itself, with out the necessity to develop the harmful pathogen.

Dr. Conley’s memos about Mr. Trump appear to indicate that the president is not producing samples with detectable subgenomic RNA. Researchers have additionally tried to tradition the coronavirus exterior of his physique, though few particulars on this have been shared. Virus that may be cultured is just not essentially transmittable, or vice versa.

Neither viral tradition nor subgenomic RNA exams are permitted for widespread use, Dr. Garner famous. Researchers doing these research may not carry out their experiments in the identical approach, making any outcomes troublesome to interpret with out extra data how, and by whom, they had been obtained.


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