Study finds evidence of fecal aerosol COVID-19 transmission

An outbreak of COVID-19 in an apartment building in China may have been caused by fecal aerosol transmission through bathrooms connected by drainage pipes, according to research published in the Annals of Internal Medicine.

“To prevent such transmission, bioaerosols can be controlled at the source by avoiding any potential gas leaks from the drainage system to indoor spaces,” Min Kang, MSc, of the Guangdong Provincial Center for Disease Control and Prevention in China, and colleagues wrote.

Kang and colleagues conducted an epidemiologic survey and a quantitative reverse transcriptase polymerase chain reaction analysis on throat swabs obtained from study participants to evaluate the temporal and spatial distributions of infected families living in a high-rise apartment building in Guangzhou, China. They also sought to identify environmental variables that may confirm the role of fecal aerosols in these transmissions.

The researchers collected the dates of symptom onset in nine residents from three families in vertically aligned apartments who were infected from January 26 to February 13. They also collected data on travel and exposure history, demographic information and any symptoms experienced by infected residents. Additionally, they examined floor plans, site plans, drainage system information, weather data and CCTV records from elevators in the building.

Later, Kang and colleagues performed airflow and dispersion tests using a tracer gas to mimic SARS-CoV-2 droplets in gas in the drainage systems.

They found that one of the three families with infected persons had traveled to the COVID-19 epicenter in Wuhan, while the other two families did not have a history of travel and developed symptoms later than the first family. The families did not know each other, and CCTV records showed that they did not use the elevator at the same time when they were potentially infectious.

None of the other 217 residents and staff who participated tested positive for COVID-19, according to the researchers.

All but one SARS-CoV-2-positive environmental samples were taken from master bathrooms in the apartments, suggesting that exposure likely occurred there. All three apartments with residents who had COVID-19 were connected through drainage stacks and vents.

Kang and colleagues did not identify evidence of transmission in the elevator or in other locations in the building.

After releasing the tracer gas into the drainage stack through a pipe in a toilet, the researchers determined that bioaerosols could travel to other apartments through the drainage pipes.

Kang and colleagues concluded that the identified infections and locations where SARS-CoV-2-positive samples were taken were consistent with vertical spread of aerosols with the virus through vents. They added that the fecal aerosols containing the virus were likely produced in the vertical stack connecting the apartments when a toilet was flushed after being used by an infected patient.

In an editorial accompanying the study, Michael Gormley, PhD, CEng, director of the Institute for Sustainable Building Design at Heriot-Watt University in the United Kingdom, said, “Kang and colleagues describe a situation in which infectious aerosols may have been formed as the result of turbulent flows within a wastewater plumbing system containing virus-laden feces.”

Gormley said the research adds “to the growing body of evidence that wastewater plumbing systems, particularly those in high-rise buildings, deserve closer investigation, both immediately in the context of SARS-CoV-2 and in the long term, because they may be a reservoir for other harmful pathogens.”

References:

• Kang M, et al. Ann Intern Med. 2020;doi:10.7326/M20-0928.
• Gormley M. Ann Intern Med. 2020;doi: 10.7326/M20-6134.