‘A Smoking Gun’: Infectious Coronavirus Retrieved From Hospital Air

Skeptics of the notion that the coronavirus spreads through the air — including many expert advisers to the World Health Organization — have held out for one missing piece of evidence: proof that floating respiratory droplets called aerosols contain live virus, and not just fragments of genetic material.

Now a team of virologists and aerosol scientists has produced exactly that: confirmation of infectious virus in the air.

“This is what people have been clamoring for,” said Linsey Marr, an expert in airborne spread of viruses who was not involved in the work. “It’s unambiguous evidence that there is infectious virus in aerosols.”

A research team at the University of Florida succeeded in isolating live virus from aerosols collected at a distance of seven to 16 feet from patients hospitalized with Covid-19 — farther than the six feet recommended in social distancing guidelines.

The findings, posted online last week, have not yet been vetted by peer review, but have already caused something of a stir among scientists. “If this isn’t a smoking gun, then I don’t know what is,” Dr. Marr tweeted last week.

But some experts said it still was not clear that the amount of virus recovered was sufficient to cause infection.

The research was exacting. Aerosols are minute by definition, measuring only up to five micrometers across; evaporation can make them even smaller. Attempts to capture these delicate droplets usually damage the virus they contain.

“It’s very hard to sample biological material from the air and have it be viable,” said Shelly Miller, an environmental engineer at the University of Colorado Boulder who studies air quality and airborne diseases.

“We have to be clever about sampling biological material so that it is more similar to how you might inhale it.”