Transmission risks of respiratory infectious diseases could be up to three times higher in confined spaces than open spaces, a local study found.

The research duo -- Moon Jin-young, leader author as a medical resident at the Seoul St. Mary’s Hospital’s Occupation and Environmental Medicine Department, and Ryu Byung-han, corresponding author as a professor at the Internal Medicine at the Gyeongsang National University Changwon Hospital -- analyzed 147 articles published until December 2020 concerning respiratory infectious diseases’ transmission risks.

A local study showed that the transmission risks of respiratory infectious diseases are up to three times higher in confined spaces than open spaces.
A local study showed that the transmission risks of respiratory infectious diseases are up to three times higher in confined spaces than open spaces.

The researchers found that the transmission risk in all types of confined spaces was about three times higher than in open areas. Specifically, the relative risk of infection was 3.94 times higher in the workplace or school, 3.23 times higher in hospitals, 3.08 times higher in airplanes, 2.63 times higher in residential spaces, and 2.17 times higher in passenger ships or navy ships.

By type of pathogen, the MERS (Middle East Respiratory Syndrome) virus caused the highest risk of transmission indoors with 12.58 times higher risk, followed by Bordetella pertussis. This pathogen causes whooping cough, with a 7.08 times higher risk.

Mumps virus was next with 4.84 times higher risk, Covid-19 virus with 4.08 times higher risk, SARS (Severe Acute Respiratory Syndrome) virus with 2.86 times higher risk, tuberculosis with 2.71 times higher risk, and influenza, 2.2 times higher risk.

The researchers grouped similar pathogens to analyze the transmission risk in indoor spaces more accurately.

The risk of infection in residential spaces was the highest at 5.14 times, followed by hospitals at 4.19 times, in contrast to the fact that the risk of transmission of all pathogens was highest at the workplace or school.

This indicates that if state quarantine measures lock down a specific type of space, the risk of infection could increase in other types of areas, the researchers said.

In the TB group, the workplace or school had the highest transmission risk with 3.88 times higher risk, followed by airplanes with 3.77 times higher risk, hospitals with 2.96 times higher risk, and residential spaces with 2.19 times higher risk.

A separate analysis of the Covid-19 virus showed a 4.08 times higher risk in confined spaces than open spaces.

By type of space, residential spaces were most risky with a 8.3 times higher risk, and airplanes had a 7.30 times higher risk.

In contrast, navy ships and hospitals showed low transmission risks, with 1.8 times and 1.78 times higher risk, respectively.

“This study is the first to quantitatively analyze the risk of the transmission of Covid-19 by droplets and air in various types of space. In addition, it is meaningful in that the study systematically analyzed the transmission risk by all respiratory pathogens in confined spaces,” said Moon.

The health authorities should particularly consider the possibility of the “balloon effect,” where a lockdown of one space leads to a concentration of people in another area, he noted.

The study will be published in the November issue of Environmental Research, and the online version was published on July 12.

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