The role of air pressure transients on the spread of bacteria from wash-hand basin sink traps in hospital en-suite bathrooms: A laboratory-based pilot study

Background
There is growing evidence for the involvement of sink and wash-hand basin traps in the spread of hospital-acquired infections in clinical settings. This pilot study used a full-scale model of a hospital wash-hand basin and wastewater drainage system, typical in single-occupancy hospital bathrooms, to examine bacterial transmission from sink traps to wash-hand basins during drainage system air pressure surges.

Methods
Simulating real-world conditions in a laboratory, a 50-m pipe network was connected to the model en-suite bathroom. Air pressure surges were generated within the pipe connection to the sink trap containing Pseudomonas alloputida KT2440 as a safe model bacterium. Measurements were made of air pressure, aerosol levels, and viable bacterial counts of the sink appliance using contact plates.

Results
Positive air pressure surges allowed water from the sink trap containing P. alloputida KT2440 to enter the wash-hand basin. Positive air pressure surges generated aerosols above the sink trap strainer. The strainer became contaminated without visible water ingress. Aerosols formed even without visible water, indicating sub-strainer agitation. Bacteria from the sink trap spread to surfaces, with viable cells recovered. Pressure surges occur naturally and increase with activities such as drain jetting.

Conclusions
For the first time, it was shown that air pressure surges in wastewater drainage systems can spread bacteria from contaminated sink traps to wash-hand basins, particularly via aerosols. This emphasizes the need for a re-examination of hospital wastewater drainage system design and maintenance in order to mitigate this mechanism of contamination.