Study: COVID-19 Airborne Transmission 1,000 Times Higher Than Surface Contact

According to results of a two-year study conducted by researchers at the University of Michigan’s School of Public Health in Ann Arbor, the risk of air transmission from SARS-CoV-2, the virus behind the COVID-19 pandemic, is 1,000 times higher than surface transmission.
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Jianfeng Wu, a research fellow at U-M’s School of Public Health, collects samples of surfaces around U-M’s Ann Arbor campus. // Courtesy of Chuanwu Xi/U-M School of Public Health
Jianfeng Wu, a research fellow at U-M’s School of Public Health, collects samples of surfaces around U-M’s Ann Arbor campus. // Courtesy of Chuanwu Xi/U-M School of Public Health

According to results of a two-year study conducted by researchers at the University of Michigan’s School of Public Health in Ann Arbor, the risk of air transmission from SARS-CoV-2, the virus behind the COVID-19 pandemic, is 1,000 times higher than surface transmission.

The study looked at public spaces on U-M’s Ann Arbor campus, including classrooms, rehearsal rooms, cafeterias, buses, gyms, student activity buildings, and ventilation and air ducts.

The researchers say because the study was conducted during lockdowns in a college campus, no samples were collected in spaces with large gatherings of people and some samples were only collected when few people were present. Also, extrapolation to the general population and health care settings should be done with caution, they say.

“We also found that the total case number of campus was significantly higher in weeks with positive environmental samples than in nonpositive weeks,” says Chuanwu Xi, professor of environmental health sciences and global public health at the U-M School of Public Health.

“Considering the recurring epidemics caused by respiratory infectious diseases in recent years, our study reinforces the relevance of integrating multiple environmental surveillance methods for modeling and risk assessment.”

For air samples, Xi and colleagues used wetted wall cyclone bioaerosol samplers, which suck in large volumes of air using a pump and capture any virus particles in the air. For surfaces, researchers used swab kits.

In all, between August 2020 and April 2021, the researchers collected 256 air samples and 517 surface samples. They found that positivity rates were 1.6 percent and 1.4 percent, respectively, and that probability for infection was about 1 per 100 exposures to SARS-CoV-2 aerosols through inhalation and as high as 1 in 100,000 from contaminated surfaces in simulated scenarios.

“Our results are a valuable addition to our understanding of infectious diseases and mitigation efforts during this pandemic, and can help prepare us for future outbreaks of respiratory diseases with similar transmission mechanisms,” says Rick Neitzel, professor of environmental health sciences and global public health at the School of Public Health.

“This is another layer of sophistication to evaluate major routes of transmission and to identify physical spaces where risks are higher and control measures in such space are essential and more effective to reduce the spread of the virus.”

In addition to Xi and Neitzel, authors included Xin Zhang, Jianfeng Wu, Lauren Smith, Xin Li, Olivia Yancey, Al Franzblau and Tim Dvonch, all with the Department of Environmental Health Sciences at U-M’s School of Public Health. The results are published in the current issue of Journal of Exposure Science and Environmental Epidemiology.

Click here to access the study.

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