The World Health Organisation (WHO) is considering “airborne precautions” for medical staff after a new study showed the coronavirus can survive in the air in some settings.

The virus is transmitted through droplets, or little bits of liquid, mostly through sneezing or coughing, Dr Maria Van Kerkhove, head of WHO’s emerging diseases and zoonosis unit, told reporters during a virtual news conference on Monday. The everyday person shouldn’t be concerned, but medical professionals may be susceptible when performing certain procedures, in certain situations.

According to Van Kerkhove, “When you do an aerosol-generating procedure, like in a medical care facility, you have the possibility to what we call aerosolise these particles, which means they can stay in the air a little bit longer.”

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She added: “It’s very important that healthcare workers take additional precautions when they’re working on patients and doing those procedures.”

World health officials say the respiratory disease spreads through human-to-human contact, droplets carried through sneezing and coughing as well as germs left on inanimate objects. The coronavirus can go airborne, staying suspended in the air depending on factors such as heat and humidity, they said.

In a separate incident in the US, Adam Burdick, a choir conductor, informed the 121 members in an e-mail that amid the “stress and strain of concerns about the virus,” practice would proceed as scheduled at Mount Vernon Presbyterian Church.

Sixty singers showed up. A greeter offered hand sanitiser at the door, and members refrained from the usual hugs and handshakes.

“It seemed like a normal rehearsal, except that choirs are huggy places,” Burdick recalled. “We were making music and trying to keep a certain distance between each other.”

After two and a half hours, the singers parted ways at 9 pm.

Nearly three weeks later, 45 have been diagnosed with COVID-19 or ill with the symptoms, at least three have been hospitalised, and two are dead.

The outbreak has stunned county health officials, who have concluded that the virus was almost certainly transmitted through the air from one or more people without symptoms.

In interviews with the Los Angeles Times, eight people who were at the rehearsal said that nobody there was coughing or sneezing or appeared ill.

Everybody came with their own sheet music and avoided direct physical contact. Some members helped set up or remove folding chairs. A few helped themselves to mandarins that had been put out on a table in back.

Experts said the choir outbreak is consistent with a growing body of evidence that the virus can be transmitted through aerosols — particles smaller than 5 micrometers that can float in the air for minutes or longer.

A study published March 17 in the New England Journal of Medicine found that when the virus was suspended in a mist under laboratory conditions it remained “viable and infectious” for three hours — though researchers have said that time period would probably be no more than a half-hour in real-world conditions.