The COVID-19 pandemic has challenged health systems and public health authorities worldwide. When you have a rapidly spreading virus with a high transmission rate, you have to investigate all possible infection risks.

One area of risk that is yet to receive any attention is big buildings such as tower blocks or hospitals. While direct person-to-person transmission is still the most common way of acquiring the illness, our research suggests that occupants in tall buildings could become infected if defects occur in the plumbing system. It’s important for people to be aware of this and take steps to keep themselves safe.

Our work at the Institute for Sustainable Building Design at Heriot-Watt University stems from an outbreak of the SARS virus in 2003 at an apartment block in Hong Kong, known as Amoy Gardens. In a building complex ranging from 33 to 41 stories with some 19,000 residents, there were more than 300 confirmed cases and 42 deaths—around one-sixth of all SARS infections and fatalities on the island as a whole.

The World Health Organization (WHO) report into the SARS pandemic suggested that defects in the wastewater plumbing at Amoy Gardens were the main cause of the outbreak. Where normally U-bends in sinks and toilets contain water that blocks airborne diseases from rising up from the sewer system, a large number of the U-bends in bathrooms at Amoy Gardens had been dry.

The WHO report suggested that when people infected with SARS had diarrhea in the toilets in the building, airborne “virus-laden droplets” could move via the sewer and plumbing network from one apartment to another. This airborne transmission route was aided by bathroom extraction fans which drew contaminated air into rooms.

Our work

On the back of this tragedy, our group has been investigating the cross-transmission of infections within buildings for nearly 20 years. Together with my co-researchers, David Kelly and Thomas Aspray, we published results in 2017 from an experiment on a full-scale two-story wastewater plumbing test rig. We used a model organism to represent pathogens flushed into the system, while putting in place the same sort of defective conditions as the Hong Kong block.

Sure enough, this showed that such organisms can be transmitted between rooms on different floors of a building through the airflow system that helps water to move around the plumbing. Not only were the organisms in the air in rooms, the droplets contaminated surfaces in these rooms and inside the system itself.