Prime focus now on airborne coronavirus transfer

Victorian health authorities have few clues on just how the quarantine support worker in Melbourne who was infected at the Grand Hyatt came to catch coronavirus from a positive guest, but they’re treating the case as a likely example of airborne transmission.

At the same time across town, COVID-19 spread between guests on the same floor at the Park Royal Hotel, even though they were at no time within physical proximity of each other.

The infection of a quarantine hotel security guard in Perth is also considered airborne transmission.

The cases highlight how easily COVID-19 can be transmitted through the air, and raise questions as to whether ventilation is adequate in quarantine hotels.

Many doctors have been highly critical of the advice of the Australia’s Infection Control Expert Group that emphasises droplet and contact spread of COVID-19, rather than recognising that the airborne method is a primary mode of transmission.

Workers in hotel quarantine and those transporting corona­virus patients still wear only surgical masks, which do not offer full airborne protection.

Early in the pandemic, the World Health Organisation stressed that SARS-CoV-2 spread most through larger respiratory droplets that land on bystanders or fall to the ground when a person coughs or sneezes.

Larger respiratory droplets are also emitted when people shout, speak loudly or sing.

However, as more was understood about COVID-19 transmission, the US Centres for Disease Control and other public health bodies around the world recognised the airborne route was the primary mode of transmission.

The CDC and the European Centre for Disease Prevention and Control both recommend airborne precautions — N95 or P2 masks — for any situation involving care of COVID-19 patients. This is contrary to Australian guidelines, which recommend surgical masks only, except in cases where the care of a patient involves an aerosol-generating procedure such as intubation.

Airborne spread of COVID-19 occurs when microdroplets emitted when an infected person talks or breathes travel through and remain suspended in the air. While transmission via direct or indirect contact occurs in a short range, airborne transmission via aerosols can occur over an extended distance and time. This explains why the Perth security guard could have become infected sitting several metres away from a room housing positive COVID-19 patients.

It’s thought airborne microdroplets can remain suspended in the air for prolonged periods, even as long as an entire day in a poorly ventilated indoor space. People become infected when they inhale these microdroplets.

Victorian authorities have taken steps to ensure the airconditioning at quarantine hotels does not recycle air from guests’ rooms to communal spaces, but the fact that in many of these hotels there is no fresh air ventilation presents a significant problem.

Aerosol scientist Lidia Morawska says addressing the challenges of airborne transmission of COVID-19 is more difficult than surface cleaning measures instituted to combat surface transmission, which are now understood to be largely pointless.

“It is … much more complicated than cleaning surfaces or wearing masks,” she says. “Steps need to be taken to understand what the ventilation is in buildings, whether the ventilation in shared spaces is adequate, and if not, spaces need to be retrofitted.”