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Figure 2: The high-rise Amoy Gardens apartments in Hong Kong where a SARS outbreak occurred in 2003, affecting over 300 residents. To the right is the layout of the apartments on each floor; transmission did not occur to other residents on the same floor. The red arrow indicates that transmission occurred to residents above and below the index cases apartment.
in faecal contamination of water supplies, and diseases such as cholera becoming rife. The ‘Great Stink’ of 1858 was the driver for Sir Joseph Bazalgette to be employed to build the sewerage system for London, which still stands today. In 2007 the British Medical Journal asked readers to nominate the most important medical milestones since the forerunner of the journal was first published in 1840. Out of a shortlist of 15 topics, clean water and sewage disposal – the ‘sanitary revolution’ – won. Two notable reports of outbreaks were with highly antibiotic-resistant strains of Pseudomonas aeruginosa. The first, by Hota et al (2009), showed that splashes from clean water hitting a contaminated drain could disperse organisms at least a metre.3
The second, from Breathnach
et al (2012), described how the wastewater system could act as a superhighway for moving organisms around a healthcare facility.4
Manchester Royal infirmary has been an ongoing source of Carbapenemase Producing Enterobacteriaceae (CPE) for over a decade. This has had a huge financial impact, as well as a detrimental effect on patient care and outcomes. The hospital’s wastewater system has had a significant role in driving this continued outbreak. The risk from wastewater systems can arise anywhere in the building, and does not need to be in the patient’s immediate
environment. The photo in Figure 1 shows how patient water jugs are traditionally filled, with placement in a sink. As the blue arrow shows, this results in the base of the jug contacting the drain and associated organisms. Outbreaks have been linked to this practice, with the jug transporting the organisms to the patient environment. Without new designs this method of filling receptacles with water is likely to continue.
Microorganisms using wastewater systems as a superhighway? It would be comforting to believe that when material disappears down a drain it is no longer a threat. However, this is not the case. There are three common potential associated ways that microorganisms effectively utilise wastewater systems as their own ‘superhighway’, as follows:
n 1: Updraught when a toilet is flushed When a toilet is flushed on the second floor of a building, for instance, and faeces and water enter the main sewage stack, one might rightly expect that the water and faecal material will fall down the stack due to gravitational forces. Indeed this occurs, but the body of water and faecal material displaces air upward within the stack, which creates an updraught that generates an aerosol of faeces and water, which can spread to multiple stories within the building. In the first SARS outbreak, biologically active virus
was excreted from the gastrointestinal tract. An immunocompromised patient infected with the virus living in a high-rise apartment in Amoy Gardens in Hong Kong (Figure 2) caused an outbreak among residents of the building. The residents living on the same floor of the building who shared services such as lifts were not affected. The pattern of spread was to residents living immediately above and below the apartment. The investigation into the outbreak
attributed the cause to spread via the wastewater system. The bathroom floors in the flats were meant to be wet mopped, and were linked to the wastewater system via a U-bend. Most residents did not wet mop the bathrooms, so the U-bend was dry. When the index cased used toilet and aerosol of faeces and virus ascended and descended the main sewage stack, the viral aerosol entered the bathrooms of the residents above and below through the wastewater system. Work conducted in Edinburgh using bacterial suspensions has shown that indeed aerosols are generated which can ascend several stories in a building, and enter other sewage pipes entering the main stack.
n 2: Spread along pipework Utilising a gallery of sinks, as shown in Figure 3, researchers inoculated the U-bend of the sink on the right with a tracer organism. Within seven days the same organism could be found in the U-bend of the three adjoining sinks. To reach the U-bend of the sink to the left required organisms to traverse an uphill gradient.
Detected within 7 days of inoculating first sink trap
Figure 3: Utilising a gallery of sinks as shown above, researchers inoculated the U-bend of the sink on the right with a tracer organism. Within seven days the same organism could be found in the U-bend of the three adjoining sinks.
n 3: Escaping from the U-bend Research from the US (see Fig 4) has shown that placement of bacteria alone in a U-bend poses no risk by itself. However, the addition of a carbon source results in a dramatic development – bacteria in the form of biofilm will ascend the drain to reach the sieve in a sink at the rate of 1 mm / hour. Water from an outlet hitting the drain will result in widespread dispersion (up to 2 metres) of the bacteria.
April 2023 Health Estate Journal 41
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