OOSKAnews Voices is a series of guest columns written by senior participants in different parts of the international water community. In this article, Dr Michael Gormley describes how management of plumbing systems within buildings can be deployed to limit transmission of infectious pathogens.
Over the last 20 years or so, one of the areas I have focused on is research aimed at improving the performance and safety of building drainage systems, particularly tall buildings, which by their very nature are engineering challenges. Two facts about these systems are rarely understood, the first is that air is as important in a wastewater plumbing system as water, and second, that the small amount of water in the U-bends under sinks, baths, showers and toilets, is the main defense against the ingress of foul or contaminated air into the interior of the building from the wastewater plumbing system and sewer. The challenge for designers is to specify a system which will minimize air pressure fluctuations and protect the water in U-bends.
While foul smells are often a nuisance, the emergence of the SARS-CoV-2 virus at the end of 2019 and the disease that it causes COVID-19 have given this a different level of importance, particularly in light of our research on infection spread in tall buildings which we recently reported in the Lancet Global Health. In particular we have identified a transmission pathway for bacteria and viruses (like SARS-CoV-2) through defects, like empty U-bends.
The identification of the wastewater plumbing system as a potential transmission pathway for pathogens goes back to the SARS outbreak of 2002-2003 and one building which raised concerns at the time. In 2003, the World Health Organisation (WHO) published a final report into a superspreading event of SARS within a housing block in Hong Kong. The 41-storey building had over 300 confirmed cases of SARS and 42 deaths. The report identified defects in the wastewater plumbing system as a transmission mode within the building which facilitated the transport of ‘virus laden droplets’ through empty U-Bends in bathrooms. This airborne transmission route was aided by bathroom extract ventilation which drew contaminated air into the room. Since then, our research group has been working on investigating mechanisms of cross transmission, improvements in system design, and innovations in system monitoring, including confirmation of the wastewater plumbing system as a reservoir for pathogens.
In 2017, we published results from an experiment on a full scale two-storey wastewater plumbing test-rig in which we used a model organism to represent pathogens flushed into the system. Viable organisms were shown to be transmitted between rooms on different floors of a building being carried within the system airflow, under defect conditions similar to those found in the SARS case in Hong Kong. Droplet fallout resulted in contamination of surfaces within the system and rooms.
In that paper, published in PLoS One, we also suggest causes of the wastewater plumbing system defects and presented a basic qualitative risk assessment for disease spread in buildings. One significant factor identified was the interconnectedness of all parts of the building by the wastewater plumbing system and, therefore, the potential for contaminated air to travel throughout the building unhindered.
So, the potential for a substantial viral load within the wastewater plumbing system (and therefore the main sewer system), in combination with the potential for airborne transmission due to aerosolisation of the virus, calls for wastewater plumbing systems to be considered as a potential transmission pathway for COVID-19.The interconnectedness of the wastewater plumbing network can facilitate exposure to SARS-CoV-2 within, or even between, buildings. This is of particular concern in high-risk transmission settings such as hospitals and health-care buildings.
So, what is the long-term solution to this issue? Given that the industry has been aware of this for 17 years with little change, what should happen now? In my view the issue is one of regulation. There are virtually no regulations on internal plumbing systems once installed. This lack of regulation would be unthinkable in water supply systems in buildings, so now is the time to start thinking about how to overhaul codes and standards and introduce regulations for wastewater plumbing systems inside buildings - before the next inevitable pandemic.