Better ventilation in public venues may be needed after growing evidence around the potential for long-distance transmission of COVID-19, research out today says.
A team of researchers from the UK Health Security Agency and the University of Bristol while evidence 18 existing studies was deemed to be of very low certainty, it is possible for an individual with COVID-19 to infect others more than two metres away in indoor, non-healthcare settings.
Writing in the latest edition of The BMJ, they call for more investigation into the potential for long distance airborne transmission of SARS-CoV-2.
Short-range transmission of under two metres can occur through both droplets and aerosols in the air, but there is no agreement about the importance of long distance airborne transmission in indoor settings.
The research team focused on 18 observational studies of COVID-19 outbreaks in countries across Asia, Europe, Oceania and the USA that were published between January 2020 and January 2022.
These outbreaks happened within a number of settings, including flats in apartment blocks, quarantine hotels, restaurants, buses, a food processing factory, a courtroom, a fitness facility, and during singing events.
They concluded that long-distance airborne transmission was likely to have occurred for some or all transmission events in 16 out of 18 studies, but it was unclear in the other two studies.
Out of the 16 studies, they found that insufficient air replacement, directional air flow, and activities associated with increased emission of aerosols, such as singing or speaking loudly, were likely to have increased the risk of transmission.
In 13 studies, the individuals who were likely to be the source of infection were reported as being asymptomatic, pre-symptomatic, or just starting to have symptoms at the time of transmission.
While the authors say their review has some limitations, such as it looked only at epidemiological observational studies of real world human-to-human transmission events before vaccine rollouts and did not include wider evidence from environmental or experimental studies, it critically assessed the likelihood of long distance airborne transmission of SARS-CoV-2 using a range of evidence.
They say their rapid systematic review shows that existing evidence of long-distance airborne transmission of SARS-CoV-2 can occur in indoor settings and that factors such as insufficient air replacement that can contribute to transmission.
“These results support the role of mitigation measures in indoor settings, such as adequate ventilation,” they write.
Duval D, Palmer JC, Tudge I et al. Long distance airborne transmission of SARS-CoV-2: rapid systematic review. BMJ 30 June 2022; doi: 10.1136/bmj-2021-068743
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