Study on ‘long-range’ airborne transmission of SARS-CoV-2 highlights the need for better ventilation

Some public places may need better ventilation to prevent the spread of Covid-19, following growing evidence of the potential for long-distance airborne transmission of the disease, research published today by The BMJ suggests.

A review of 18 existing studies indicates that airborne transmission of the SARS-CoV-2 virus from an infectious person to others more than two meters away can occur in a variety of indoor non-healthcare settings.

However, the researchers emphasize that the evidence from these studies was considered very low certainty, and say that further research into the potential for long-range airborne transmission of SARS-CoV-2 is needed.

Since the early stages of the Covid-19 pandemic and the so-called ‘superspreader’ events, there is growing evidence that airborne transmission of the SARS-CoV-2 virus in places with poor ventilation has contributed to its spread. of infections.

It is generally accepted that short-range transmission (less than two meters away) can occur via both droplets and aerosols in the air, but there is no agreement on the importance of long-range airborne transmission (more than two meters) indoors . such as catering establishments, leisure facilities, workplaces or apartment buildings.

A team of researchers from the UK Health Security Agency and the University of Bristol therefore set out to explore the potential for long-distance transmission of SARS-CoV-2 in indoor environments and to investigate factors that could influence transmission.

They reviewed studies on the topic published between January 2020 and January 2022, focusing on 18 observational studies of covid outbreaks in countries in Asia, Europe, Oceania and the US.

These outbreaks occurred in a variety of community settings, including condominiums in condominiums, quarantine hotels, restaurants, buses, a food processing factory, courtroom, fitness center, and during singing events.

The review authors concluded that long-range airborne transmission likely occurred for some or all transmission events in 16 of the 18 studies. It was unclear in the other two studies.

In the 16 studies, one or more factors were likely to have increased the likelihood of long-range air transmission, most notably insufficient air replacement, directed airflow, and activities associated with increased aerosol emissions, such as singing or speaking loudly.

In 13 studies, the individuals likely to be the source of infection were reported to be asymptomatic, presymptomatic, or just beginning to have symptoms at the time of transmission.

The review has some limitations, for example it only looked at epidemiological observational studies of human-to-human transmission in the real world and did not include broader evidence from environmental or experimental studies.

In addition, most outbreaks occurred before the introduction of the vaccine and it is unclear how these results apply to populations with high levels of immunity to infection, either naturally derived or vaccine-mediated.

Nevertheless, the review critically assessed the likelihood of long-range airborne transmission of SARS-CoV-2 using a range of evidence from epidemiological data, genomic analysis and video surveillance to analysis of seating arrangements and testing of environmental hypotheses.

As such, the authors conclude: This rapid systematic review demonstrates the existing evidence that long-distance airborne transmission of SARS-CoV-2 can occur in indoor environments such as restaurants, workplaces and venues for choirs, and identified factors such as insufficient air exchange that can contribute to the transfer.

“These results support the role of mitigation measures in indoor environments, such as adequate ventilation,”

Now is the time for an indoor air revolution, says Stephanie Dancer, Consultant Microbiologist at Edinburgh Napier University, in a linked editorial.

She also points out some study limitations, but says “the evidence presented in this review, weak as it is, confirms the premise that small respiratory particles containing SARS-CoV-2 are freely transmitted through insufficiently ventilated environments.

It is hoped that public health leaders will develop practical guidelines and “tilt” people and places closer to safety.


Stephanie Dancer, Consultant Microbiologist, Edinburgh Napier University

Source:

Reference magazine:

Duval, D., et al. (2022) Long-range airborne transmission of SARS-CoV-2: rapid systematic review. The BMJ. doi.org/10.1136/bmj-2021-068743

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