Health officials in Hong Kong are working with several agencies to determine whether coronavirus disease 2019 (COVID-19) is capable of spreading through buildings via ventilation and piping systems.

The investigation comes after the city’s Center for Health Protection (CHP) diagnosed a 62-year-old woman with the viral disease. It was discovered that a vent pipe near her toilet was “altered” without landlord permission, prompting a thorough search of the 34-unit Hong Mei House apartment building. Officials have since sealed the vent.

Two other residents were found to be infected with COVID-19, bringing the Hong Kong total to more than 40 confirmed cases. One hundred other residents from the complex were sent to quarantine. (As of February 11, the World Health Organization reports that there are more than 43,000 cases worldwide.) As a precautionary measure, health officials warn others living in the apartment building to keep windows shut and avoid turning on fans and ventilation systems when using the toilet.

“The public is strongly urged to maintain at all times strict personal and environmental hygiene which is key to personal protection against infection and prevention of the spread of the disease in the community,” said a CHP spokesperson in a statement.

“As for household environmental hygiene, members of the public are advised to maintain drainage pipes properly and regularly pour water into drain outlets (U-traps); after using the toilet, they should put the toilet lid down before flushing to avoid spreading germs." 

Severe acute respiratory syndrome (SARS), another coronavirus outbreak that struck parts of the world in 2003, was found to spread through the Amoy Gardens apartment complex in China through ventilation and piping systems originating in the bathroom. This occurred in two ways, according to a study published in the Journal of the Royal Society of Medicine. First, respiratory droplets from contaminated individuals were believed to mix with water vapor from showers, spreading throughout the complex by fans and ventilation systems. Second, U-shaped pipes under sinks, known collectively as “u-traps”, acted as reservoirs for the virus. U-traps meant to retain fluid to prevent sewer gases from entering the building instead may have resulted in the virus spreading back into the system. Much like SARS, COVID-19 is believed to be spread through contact with respiratory droplets and feces. 

However, the Hong Kong Free Press reports that an expert with the University of Kong’s Department of Microbiology says that the two confirmed Tsing Yi cases are not similar and that the U-shaped water traps at Hong Mei were functional.

Although the World Health Organization reports that new cases in China are stabilizing, the COVID-19 death toll has already exceeded that of SARS. Currently, people entering Hong Kong from mainland China are required to undergo a 14-day quarantine and residents are advised to “go out less and reduce social activities.” CHP says it is still investigating the situation and residents are encouraged to maintain drainage pipes properly and regularly to ensure environmental hygiene. After using the toilet, residents should also put the toilet lid down before flushing to avoid spreading the virus.