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 check will carry out in individuals outdoors this window. Mr. Trump obtained a number of of those exams throughout his second week of sickness, all of which returned damaging outcomes.

“The exams have for use after they’re supposed for use,” stated Andrea Prinzi, a medical microbiologist on the College of Colorado, Anschutz. “That’s after they’re going that will help you probably the most.”

Each 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 lively. Some individuals who have been contaminated by the coronavirus might register as P.C.R. constructive for weeks, even months, after they are no longer contagious or ill, just because exams are selecting up on innocent souvenirs of an an infection gone.

“Neither is a measure of precise, reside 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 an individual’s airway after which attempt to coax the coronavirus into infecting cells in a lab. However these procedures aren’t extensively out there to the general public, as a result of they should be carried out in a high-containment facility by individuals particularly skilled 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 outdoors of his physique, though few particulars on this have been shared. Virus that may be cultured isn’t essentially transmittable, or vice versa.

Neither viral tradition nor subgenomic RNA exams are authorised for widespread use, Dr. Garner famous. Researchers doing these research won’t carry out their experiments in the identical manner, making any outcomes troublesome to interpret with out extra info how, and by whom, they had been obtained.

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