Pseudomonas aeruginosa in hospital water systems: biofilms, guidelines, and practicalities

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Summary

Pseudomonas aeruginosa is one of many micro-organisms that can act as an opportunistic pathogen and colonize and infect vulnerable patients. Hospital water is a recognized source P. aeruginosa. Several outbreaks, including the incidents involving babies in Northern Ireland in 2011/12, have been attributed to contaminated water systems. As a direct result of the deaths of four neonates in Northern Ireland, guidance documents ‒ addendums to Health Technical Memorandum 01-04 (Department of Health, England) ‒ were produced to advise National Health Service managers on how to deal with the presence of P. aeruginosa in augmented care units. The guidance was based on current expert opinion and limited scientific evidence. Public Health England has established a reproducible and controllable water distribution test rig in a laboratory setting to further understand the contamination of water systems by P. aeruginosa and to identify vulnerable sites for microbial colonization. It is anticipated that these studies will add to the evidence base and enable the guidance documents to be updated in due course.

Introduction

Pseudomonas aeruginosa has long been known to cause infection in vulnerable patients.1 Hospital water is a recognized source of P. aeruginosa and, following the death of four pre-term babies in Northern Ireland (NI) (2011/12), the Department of Health issued specific guidance on P. aeruginosa and water quality in augmented care units in 2012/13. However, this guidance has not been universally accepted; there is debate as to the relevance of testing the water in augmented care units for P. aeruginosa and concern about the costs of the recommended sampling programme.2

Some studies have linked acquisition of P. aeruginosa to its presence in the environment, particularly the handwash station and water outlet.3, 4, 5, 6, 7, 8, 9, 10 Others have found that strains isolated from patients frequently differ from those isolated from the environment.11 During the investigation of the NI incidents, P. aeruginosa isolates from water samples, and from biofilms colonizing the flow straighteners and other plumbing components, were found to be indistinguishable by variable number tandem repeat (VNTR) typing from those recovered from the babies.12

In 2013 the Department of Health, England, published advice on P. aeruginosa for augmented care units as an addendum to previously published guidance for the control of legionella, Health Technical Memorandum (HTM) 04-01. It incorporates a number of lessons learnt from the NI incidents.2, 13, 14 The addendum recommends, for example, that ‘ … [hospital managements] should form a water safety group (WSG), i.e. a multidisciplinary group to develop and implement a risk based water safety plan (WSP)’. Many National Health Service (NHS) hospital organizations had already established Water Groups, primarily to manage issues relating to Legionella spp. These groups have generally been the responsibility of estates departments, which are also responsible for implementing appropriate legionella control strategies. However, responsibility for control of waterborne P. aeruginosa is not confined to estates departments. Preventing transmission within the ward also requires input from those with responsibility for nursing, microbiology, housekeeping, and infection prevention and control. Micro-organisms have been present for millennia and are able to occupy a surprisingly wide range of environments. We should not let the recent waterborne incidents cloud our view of other potential routes of transmission.

The handwash station needs to be considered holistically and risk assessments have to be introduced at each stage including design, installation, utilization, and, where necessary, control measures. When designing a hospital ward, the number and distribution of handwash basins should encourage hand hygiene. To maximize opportunities for handwashing in augmented care units, there is typically one clinical handwash basin per one or two beds. However, is this actually required? Could an oversupply of handwash stations lead to some handwash basins being under-used, resulting in stagnation of water, biofilm formation and contamination of the water?15 The guidance recommends that there should be wall-mounted single-lever-action or sensor tap (with single self-draining spout) connected to a thermostatic mixing valve (TMV) approved under the Buildcert's TMV3 Approval Scheme (http://www.buildcert.com/TMV3.htm) and supplied by concealed services. The choice of water outlet is complex. Non-touch sensor-operated outlets have gained favour in the last few decades both for water economy and in the belief that the avoidance of hand contact will reduce cross-infection. However, sensor taps have been associated with a number of microbial incidents.16

Following the incidents in NI, Public Health England (PHE) was funded by the Department of Health (England) to investigate the contamination of P. aeruginosa in a water distribution test rig located in the PHE laboratories at Porton, Salisbury. The test rig was built from components similar to those used in NI and was inoculated with the same strain of P. aeruginosa that was isolated from NI to study the development of biofilm colonization of the flow straighteners. Over time there was very little colonization of the flow straighteners, yet the majority of the water samples were positive. A thorough examination of several of the different components of the test rig revealed that the rubberized ethylene-propylene-diene-monomer (EPDM) seal used in the tap solenoids was extensively colonized with P. aeruginosa. When these solenoids were removed, the water samples were negative for P. aeruginosa. The test rig is advancing our understanding of water systems and complements the studies from NI, which demonstrated that under particular circumstances, different components within a water system such as the flow straighteners and solenoid seals can become a site of P. aeruginosa biofilm proliferation.17, 18

If sensor-operated taps are to be used, the sensors must be positioned so that, when washing their hands, the user will not accidentally touch and contaminate the outlet; that is the sensor should not be installed immediately adjacent to the outlet.19 Equally, the position of the soap dispensers in relation to the water outlet should be such that users do not contribute to the build-up of soap debris and other organics on the water outlet that may lead to contamination and facilitate the survival of potential pathogens.

The location of a disposal point for waste clinical material, either from patients, medical equipment or other surfaces, must be considered. Sluice sinks should be used for the disposal of waste fluids but these are often situated at the far end of the ward and nursing staff may ‘risk assess’ that it is safer to dispose of contaminated fluids at a handwash station, potentially leading to microbial contamination with pathogens, rather than risk carrying them some distance, which may result in spillages. A number of hospital managements have dealt with this situation effectively by adding commercially available absorbent gels to wash bowls and slipper-pan containers, resulting in a solidified mass that can be disposed of via the clinical waste. Other hospital managements permit waste from patient isolation rooms to be discarded via the en-suite toilet. If waste material is disposed of via handwash basins, the waste drain may be contaminated with pathogens. The wet drain environment provides ideal conditions for biofilms to proliferate. Handwash basins should have an integral back outlet. Drains directly under flowing outlets may lead to bacteria within the drain becoming aerosolized.21 Although there is debate as to the relevance of the contaminated drain to clinical transmission, there is evidence that a number of outbreaks have been controlled by decontaminating the drain either by using chemicals or by fitting a self-decontaminating drain system.21 In addition, containers should not be placed on the surface of the handwash basin.

There is still debate about the need to monitor water for P. aeruginosa. The English guidance in the addendum to HTM 04-01 recommends six-monthly sampling, testing and monitoring of water samples whereas Scottish guidelines state that actions should only be taken on clinical outcomes.22 However, to control a problem one has to identify the source of the contamination and understand the potential routes of transmission. Where water samples are positive for P. aeruginosa there are several potential solutions. Risk assessments, based on the vulnerability of the patient and microbial bioburden, should identify the most appropriate approach to be taken. Strategies such as using sterile water to wash neonates will reduce the risk of waterborne transmission of pathogens. However, significant bacterial contamination is generally associated only with the last 2 m of plumbing from the outlet.23

Bacterial retention or point-of-use (POU) filters provide a rapid way of delivering microbiologically safe water free of P. aeruginosa. Whereas filters are considered to be a short-term solution, there have been occasions on which hospitals have not been able to achieve microbial control through engineering solutions and have adopted point-of-use filters for a number of years. POU filters may not always be appropriate. For example, their fitting may decrease the water flow rate or reduce the space available for handwashing. Although antimicrobial agents have been incorporated into filter bodies, there have been reports of the filter body itself becoming contaminated with P. aeruginosa.

Some hospitals have replaced sensor-operated outlets with lever-operated manual taps and have removed TMVs. This enables staff to adjust the water to the required temperature and for estates staff to thermally flush the outlet manually as per local protocols. Another approach has been to reduce the distance between the outlet and TMV by installing lever-operated taps with an integrated TMV.

One hospital group in Northern Ireland has retained the use of sensor-operated outlets and, in an attempt to reduce the microbial bioburden and presence of opportunistic pathogens, has been working with a company to design an outlet fed by water that passes through an ultraviolet lamp. This design has undergone a number of refinements; during a 20-month period only two of 4040 tap water samples (<0.05%) have been positive for P. aeruginosa.20 The first failure involved formation of biofilm in the collar screw threads at the tap outlet, and the second was associated with a visible calcified deposit adjacent to the outlet. Other manufacturers have re-engineered several ‘anti-Pseudomonas’ strategies including copper-lined outlets and smooth bore internal taps. However, substantial independent research in the laboratory and in hospitals is required to substantiate these claims.

The importance of regularly servicing a water system is not in doubt. Equipment used in the supply, storage and transfer of water must be maintained to ensure that there is no build-up of organics, debris, and biofilm that will facilitate the survival and growth of opportunistic pathogens including P. aeruginosa. This includes ensuring that water tanks are clean, that taps and associated components such as TMVs, outlet fittings, and filters are serviced, descaled, and decontaminated at recommended intervals. If excessive build-up of debris or biofilm is observed, then the servicing frequency may need to be increased and the cause investigated. For effective descaling and decontamination, tap outlets should be dismantled to improve the potential for biocide to gain access to the bacterial biofilms. In addition to descaling and decontamination, some hospitals place the dismantled outlets into a DIN basket (Deutsches Institut für Normung, German Institute for Standardization) and into a washer disinfector. Whereas biocides may not come into contact with every internal surface, such as those areas located under rubber washers, the elevated temperature in a washer disinfector (93°C) should reduce the microbial bioburden to a safe level. This approach enables the hospitals to have a clean, decontaminated tap to replace one that has been found to be P. aeruginosa positive. As one of the most common plumbing jobs in a healthcare establishment is the unblocking of toilets, consideration should be given to the cleanliness of plumbing tools. Cleanliness is important regardless of the vulnerability of the patient. Plumbers working in augmented care may require training to aid their understanding of infection prevention and control.

It is clear that we need to know more about the role of water and the environment in microbial colonization and infection in a clinical setting. PHE has been working with the Queen Elizabeth Hospital in Birmingham, UK, to investigate the transmission of waterborne P. aeruginosa in the non-outbreak setting. The impact of implementing HTM 01-04 guidance on the presence and transmission of P. aeruginosa in augmented care will also be investigated. The study will use whole genome sequencing to determine whether strains recovered from the water and from patients are related, the route of transmission, and whether implementing the national guidance has resulted in a reduction in the number of waterborne P. aeruginosa infections.

There has been a change of emphasis from infection control to infection prevention. Consequently there is a greater interest in the role of healthcare premises as an environment for the proliferation and transmission of pathogens. We must develop consistent strategies to eliminate these hazards, and communicate them clearly to clinical and estates staff. Such strategies require behavioural change to be effective in preventing microbial transmission.

Section snippets

Acknowledgements

The authors would like to thank many of the colleagues with whom they have worked to assist the understanding of the multiple issues related to the presence and transmission of P. aeruginosa including P. Hoffman, B. Patel, S. Atkins, G. McCracken, C. Mitchel, B. Oppenheim, and P. Ashcroft as well as thanks to K.-A. Thompson, D. Ngabo, S. Parks, and D. Stevenson for their academic and technical input.

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