Coronavirus cluster claim shrouded in mist of nebuliser ignorance

A Deakin University aerosols expert has cast doubt on the theory Victoria’s Holiday Inn COVID-19 outbreak was caused by nebuliser mist.

A Deakin University aerosols expert has cast doubt on the theory Victoria’s Holiday Inn COVID-19 outbreak was caused by nebuliser mist, saying there is no evidence to suggest it “directly increases the level of virus carried”.

Last week Victorian Chief Health Officer Brett Sutton suggested the cluster may have been sparked by a 38-year old man who used a nebuliser in hotel quarantine and later tested positive for the virus.

But David Morton, a former head of research at medical inhaler company Vectura, has disputed the theory, saying there is widespread misunderstanding about how nebulisers work. “An aerosol is simply a dispersion of material in the air, and professionals concerned with COVID-19 transmission have adopted the term ‘aerosol’ for any material small enough to remain in the air for more than a few seconds.”

However, Professor Morton argues that such dispersions are “smaller than around 100th of a millimetre – cigarette smoke, fogs and mists are examples”.

“Nebulisers don’t directly increase the level of virus carried on an aerosol. The assumption that they do is at odds with my 30 years of experience researching.”

“Nebulisers are just one of many medical procedures that generate an aerosol. Others include … a ventilator to support … breathing or an invasive bronchoscopy to extract fluid from the lungs. Those … do represent a COVID aerosol risk. Suspicion of nebulisers seems to be based on lumping together aerosol-generating procedures as if they all present a similar risk – they don’t.”

Misguided restriction of nebulisers could threaten vital therapies for asthma, chronic obstructive pulmonary disease or cystic fibrosis --- or indeed for treatment of COVID-19, said Professor Morton.