distribution system, medical device etc.). Water-related RC has three main directions, reversed to the direction of water and waste. The first is upwards the sewage system back to the drain and often into the air through aerosols (drain- directed RC). The second is towards the water outlet

from the drain, sink wall, shower cabin wall, bathtub or contaminated hands or other skin parts (water outlet-directed RC). The third direction is from the water outlet upwards the water distribution system via backflow or back growth of pathogens (water supply-directed RC).2

Sources of RC and corresponding measures The main causes of RC are the presence and growth of biofilm on surfaces near the drain and the water outlet, components of the water outlet itself and microorganism on hand and other skin parts. Measures to avoid RC can be split in two categories: preventive measures and barrier measures. Preventive measures include regular equipment cleaning/disinfection and hand hygiene procedures (washing and disinfection) as well as certain biofilm respectively standing water minimising design features and at the same time avoiding biofilm/standing water- enhancing design features and components. Barrier measures should actively retain bacteria from traveling via a barrier such as a check valve between water outlet and water distribution system, as well as splash- back minimising features or increasing traveling distance such as maximising the distance between a tap water outlet and the drain.

Handling and intended use To avoid water outlet-directed RC, POU filters and other water outlet equipment should obviously not be touched or in contact with wastewater, non-potable water or waste liquids from patients or medical devices. According to a study, 96 per cent of sinks are used for waste cleaning and other purposes than handwashing, which clearly raises questions about the current waste management in the healthcare sector.3 If visibly contaminated, water outlet equipment should be exchanged. Water outlet equipment should be

replaced regularly as a preventive measure against water outlet-directed RC. In case of POU filters, they should be exchanged according to the manufacturer’s instructions and not be reused, at least not the filter cartridge, since the membrane material makes it unsuitable for re-processing. If the housing is reused, it should be cleaned, descaled and disinfected properly, ideally by the manufacturer


Design consideration for filter mounting position, increases activity space and reduces back splashing.

itself. The same is valid for other water outlet equipment. Many water outlet components such as shower heads, shower hoses, aerators or diffusers have a colour-coding scheme to make this process easier.

Cleaning procedures As an important preventive measure especially against water outlet-directed RC, cleaning should be performed regularly on POU filters, as well as on other water outlet equipment, taps, sinks and showers. Smooth surfaces with minimal gaps between component junctions that could trap bacteria are preferable. It is estimated only a third of nurses conduct a proper cleaning procedure. Following the simple cleaning formula of ‘one side, one direction, one wipe’ makes a difference. Cleaning should ideally be performed with a disinfectant or bactericidal cleaning agent since the usual detergents or wet cloths could be pre-contaminated.

Disinfection and flushing procedures For tackling water supply-directed RC, the main preventive measures are periodic thermal or chemical disinfection and regular flushing as a non-aggressive method to minimize biofilm from stagnant water. behind the water outlet. WHO and UK health authorities recommend to flush water outlets on a daily basis.4,5 For dental practices, UK and German health authorities recommend flushing water systems for two minutes before the first patient at least 20 seconds in between patients.6,7

A nurse should ideally handwash 60 times per day minimising both cross- contamination and biofilm growth in water outlet and distribution system. There are taps available with automatic flush functions or retrofit-flush system solutions. Showers should ideally be in the ward and not in the patient room since they will probably not be used frequent enough. There are shower panels available with integrated automatic flush functions.

Back-splashing Back-splashing is probably the main reason for contaminated water outlets, especially taps. An extensive study found through genetical identification and comparison of several P. aeruginosa strains that P. aeruginosa traveled from patients’ hands to the tap water outlet (water outlet-directed RC) in 11 out of 39 taps and that carriage of P. aeruginosa by patients was both the source and consequence of colonisation in the water supply.8

Some of the strains in the tap water of one tap originated from a patient’s strain in a neighbouring patient room, which could rather mean P. aeruginosa was carried into the water supply through water supply-directed RC and colonised the piping of both rooms. More probably, however, healthcare staff not following proper hand hygiene carried them on their hands during handwashing and they travelled to the water outlets in back-splashing droplets. Another study came to the same

conclusion. It was observed that water outlet-directed RC from patients (hands, hand of healthcare worker in patient contact, patient washing water poured in sink) to tap water outlets through five, and the other way around in 18 out of 45, P. aeruginosa-infected patients.9 One important barrier measure for

water outlet-directed RC for back- splashing in sinks is the orientation of the water stream from the tap. Since most biofilm is in the drain, the water stream out of the tap outlet should not face directly into the drain hole. Back-splashing droplets can travel up to two metres away from the sink. Most POU filters are simply an elongation of the tap that is mostly vertically oriented towards the drain hole, where some POU filters enable the water stream to be positioned to the side of the sink. The first also reduces ‘activity space’ (usable distance for handwashing between water outlet, higher water level and drain hole) and increases the risk of back-splashing. Side-mounted POU filters


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