WASHINGTON: A new study examining air samples from hospital wards with COVID-19 patients has found the virus can travel up to 4m – twice the distance current guidelines say people should leave between themselves in public. The preliminary results of the investigation by Chinese researchers were published on Friday in Emerging Infectious Diseases, a journal of the US Centers for Disease Control and Prevention (CDC).

They add to a growing debate on how the disease is transmitted, with the scientists themselves cautioning that the small quantities of virus they found at this distance are not necessarily infectious. The researchers, led by a team at the Academy of Military Medical Sciences in Beijing, tested surface and air samples from an intensive care unit and a general COVID-19 ward at Huoshenshan Hospital in Wuhan. They housed a total of 24 patients between Feb 19 and Mar 2.

The team also looked at so-called aerosol transmission - when the droplets of the virus are so fine they become suspended and remain airborne for several hours, unlike cough or sneeze droplets that fall to the ground within seconds. They found that virus-laden aerosols were mainly concentrated near and downstream from patients at up to 4m – though smaller quantities were found upstream, up to 2.4m.

They also offered advice that bucks orthodox guidelines: "Our findings suggest that home isolation of persons with suspected COVID-19 might not be a good control strategy" given the levels of environmental contamination. Aerosolisation of the coronavirus is a contentious area for scientists who study it, because it is not clear how infectious the disease is in the tiny quantities found in ultrafine mist.