“The WHO report conjectured that the sanitary plumbing system was one transmission route for the virus. Empty U-traps allowed the aerosolised virus to enter households from the sewerage system”
Out of sight out of mind… Biofilm in healthcare drains are rarely maintained and have the potential of spreading even more resistant bacteria. Due to the contact time required for strong chemicals to kill biofilm, eradicating it is almost impossible. Therefore, sealing wastewater pipes becomes vital. Numerous studies stress the importance of maintaining physical barrier between drainage systems and surroundings. This means one of two things
1. Installing Automatic trap primers, which can be unreliable and a costly exercise to pre-install or retrofit
OR
2. Manually ensure someone goes around each room to CHARGE (top up) each drain trap to keep the water barrier high. This is time consuming and a waste of resources.
Green Drains TM is the ideal, cost-efficient, preventative solution compared to the above-mentioned points.
Plumbing systems, along with exposed drains are potential sources for contamination that provide a hospitable habitat for waterborne and airborne pathogens. Eg. Legionella, Listeria, SARS, MERS, Klebsiella, Dengue, Salmonella etc.
The bathroom floor drains with dried up ‘P traps’ provided a pathway through which residents came into contact with small droplets containing viruses from the contaminated sewage. These droplets entered the bathroom floor drain through negative pressure generated by exhaust fans when the bathroom was being used with the door closed. Author S H Lee PubMed – SARS epidemic in Honk Kong Aug 21, 2003
Pathogen cross-transmission via building sanitary plumbing systems
The spread of disease via building environmental systems is, on the whole, little understood. Sporadic investigations on pathogen transmission have mostly focussed on Legionella pneumophila in air conditioning and water supply systems with some additional work being carried out on biofilm formation in sinks and pathogen fallout from flushing toilets.
Fig 1. SARS transmission route at Amoy Gardens via the sanitary plumbing system.
While the study of L. pneumophila transmission from water supply systems is now well understood, principally due to the steady, predictable nature of the water flows involved, this is not the case for the transmission of pathogens from the sanitary plumbing system. These systems are characterised by unsteady and turbulent wastewater flows due to random discharges from sanitary fittings such as sinks, baths, showers, and toilets. These flows, in turn, induce unsteady transient airflows inside the plumbing pipe network. Wastewater flows inside the sanitary plumbing system lead to pressure fluctuations which can compromise the fragile water trap seals (U-traps) which form the only protection between the sanitary plumbing system and the people within buildings.
Fig 1. SARS transmission route at Amoy Gardens via the sanitary plumbing system.
Since the SARS outbreak in 2002/2003, there has been growing concern regarding the role that the sanitary plumbing system played in the transmission of the virus. The World Health Organisation (WHO) Consensus Document on the epidemiology of the outbreak included a report on the transmission of SARS in one particular housing block in Hong Kong (Amoy Gardens) which was considered as a ‘super-spreading event’. A total of 341 cases of SARS were reported at Amoy Gardens, resulting in 42 deaths. One of the reasons cited for this high infection rate was the spread of the virus via the building’s sanitary plumbing system. The WHO conjecture stated that “dry U-traps in bathroom floor drains provided a conduit for contaminated sewage droplets to enter households. A significant virus load had built up in the sewer system as an increasing number of SARS cases with diarrhoea excreted virus. Virus was aerosolized within the confines of very small bathrooms and may have been inhaled, ingested or transmitted indirectly by contact with fomites as the aerosol settled”. The U-traps (particularly in floor gullies) were found to be depleted of water, thus having lost their sealing function and providing an open connection between the sanitary plumbing system and different apartments within the building. As the number of SARS cases increased, the sanitary plumbing system became a reservoir for the virus due to diarrhoeal excretion. The WHO hypothesis followed that the virus became aerosolised when discharged into the sanitary plumbing system which provided a conduit for virus-laden aerosols to enter apartments via depleted U-traps. This process was exacerbated by the naturally occurring airflows within the sanitary plumbing system and the negative pressures within bathrooms as a result of extract fans. The combination of these factors presented a pathway for pathogen transmission heretofore unexplored. The process is illustrated in the Figure above.
Pathogen cross-transmission via building sanitary plumbing systems in a full-scale pilot test-rig. PLOS ONE | DOI:10.1371/journal.pone.0171556 February 10, 2017 Michael Gormley*, Thomas J. Aspray, David A. Kelly, Cristina Rodriguez-Gil School of Energy, Geoscience, Infrastructure and Society, Heriot-Watt University, Riccarton Campus, Edinburgh, United Kingdom