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of publication, the design of taps has beenevolving alongside growing understanding ofhow pseudomonas is transmitted via water.

The Addendum stresses that controls ofthe water system are necessary both beforeand after the outlet, including regulation ofwater temperature and flushing, and advisesregular removal/cleaning/descaling orreplacement of water outlets where there maybe direct or indirect contact with patients.

One important aspect of the discussion on

Reducing the risk ofwaterborne infection

taps has been the role of thermostatic mixingvalves (TMVs) that are integrated into tapsknown as TMTs. These integral TMVs havesometimes been found to act as focal pointsfor bacterial contamination and somefacilities have been choosing to removeTMVs altogether.

But can the benefits of TMVs incorporatedinto taps be retained while any susceptibilityfor contamination is reduced? The answer liesin innovative tap design that addresses manyof the problems of bacterial colonisation intap components. Some of the latest tapdesigns offer a solution – certain models cannow easily be isolated, de-mounted anddisassembled, then decontaminated and re-assembled.

A new piece of research now shows howthis decontamination process can be madefaster and easier.

Research at the Hospital InfectionResearch Laboratory (HIRL) at the Queen

INFECTION CONTROL

According to recent stories in The Guardianand Sun (January 30, 2016), injured militarypersonnel at the Ministry of Defence’srehabilitation centre Headley Court haveunknowingly been bathing for months in tapwater contaminated with the potentiallypathogenic bacterium Pseudomonasaeruginosa. Many of the patients at thecentre, which is reported to have hadnumerous maintenance problems, have openwounds that would be particularly susceptibleto dangerous pseudomonas infections.

Yet there are very comprehensiveguidelines on how to prevent such issues.Although the recognition of water as a sourceof pseudomonas infections has historicallybeen slow, the Department of Health’slandmark 2013 document, the Addendumto Health Memorandum 04-01 on thecontrol of Legionella: ‘Pseudomonasaeruginosa – advice for augmented careunits’, has established best practice,including risk assessments that considerwater quality in relation to high risk patients.1

Since the trigger for these guidelines camefrom the much publicised 2011/12 Belfastneonatal incident, in which the P. aeruginosainfections from which three Northern Irishbabies died were traced back to contaminatedtaps, one of the HTM 04-01 Addendum mainareas of focus has been to look at whataspects of taps might promote pseudomonasgrowth and how to prevent this happening.Because the Addendum acknowledges thatits recommendations can only be based onthe scientific knowledge available at the time

Concerns have been raised about the threat posed to patients from tapcontamination in healthcare facilities. However, a new protocol is boostingdecontamination options for thermostatic mixing taps, which could helpimprove infection prevention. Susan Pearson reports.

In healthcare facilities, water needs to becirculated to the point of use at temperaturesabove 50˚C as a primary control method to kill legionella – hence the need for TMVs to prevent scalding.

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and, either way, must be readily accessible.2

Pseudomonas and other waterbornepathogenic organisms have the ability toform biofilm, which has been discussed atsome length before in CSJ. To re-cap briefly:biofilm is a complex colony ofmicroorganisms that can ‘glue’ itself to inertsurfaces. As biofilm forms it ‘matures’ frommicro-colonies to larger films in which themicroorganisms can proliferate, withsections able to break off as ‘planktonic’waterborne components. It is these that, ifthey contain pathogenic bacteria in sufficientquantities and are discharged from outlets,can represent a risk to the most vulnerablepatients (see panel, above.)

Microorganisms may get into a watersystem in miniscule undetectable quantitiesat the point that the mains water enters abuilding and then multiply anywhere in thesystem in conditions conducive to biofilm.However, pseudomonas contamination ismost likely to occur due to contamination ofthe tip of taps when staff wash their handsafter patient care. This retrograde

Pseudomonas is a bacterium that thatoccurs naturally in many – but not all –healthy individuals without causingproblems, but can cause severe infectionsin individuals with weak immune systems,the elderly and immuno-compromisedpatients such as organ and bone marrowtransplant patients, haematology, intensivecare (ICU), oncology and cystic fibrosispatients. The organism does not occurnaturally in neonates and they are alsovery vulnerable to infection. In the clinical environment, P. aeruginosa

biofilms may form on the plastic materialsfound in prosthetics such as urinary tractcatheters and respiratory tract tubes inventilated patients, and it also grows onmoist wound surfaces such as burnswounds and diabetic ulcers.

P. aeruginosa is responsible for around10% of all healthcare-associatedinfections (HCAIs) and is responsible forup to 25% of all ventilator-associatedpneumonias (VAPs), which account foraround 50% of infections acquired onintensive care units (ICUs). Around 20%of all ventilated patients are at risk of VAP,which causes up to 40% of deaths inthese patients. 4,5

P. aeruginosa can become highly resistantto many antibiotics, constantly increasingthe dangers to those affected. Traditionally, person-to-person

transmission of P. aeruginosa infectionshas been considered difficult to control inhealthcare settings, yet evidence of thelink between water and P.aeruginosainfections in fact goes as far back as1984, when a study from an ICU in the

Pseudomonas and waterUS found 11 sinks containing multiplestrains of the organism. Some strainspersisted for weeks, while others wereisolated on just one occasion.6

The relationship between water outletsand patient infections was established morefirmly in 1993 in the Netherlands, wheregenetic fingerprinting showed water to bethe source of septicaemia in two neonates.7

There have been many subsequentreports and studies that indicate thatpseudomonas can be transmitted in water.For example, in 2004, a large three yearprospective study in Spain examined awide range of patient samples taken onadmission to a 16-bed ICU andsubsequently three times per week. Tapwater and taps were also sampled andtested for P.aeruginosa every 72 hours.ICU-acquired colonisation was found in 31patients. Pseudomonas strains were foundin over two thirds of water samples, with83% of the strains isolated from patientsshown to be acquired from the watersupply.8

In a French 2007 study on a 16-bed ICUwhere tap water was sampled weekly, itwas clear that two-way colonisation trafficbetween patients and taps was occurring.In this instance, the cause could have beendue either to contamination of taps byhealthcare workers’ hands or to body fluidsbeing tipped down hand wash basins.9

In 2010, a definitive article by ProfessorMartin Exner, Director of the Institute ofHygiene and Public Health at theUniversity of Bonn, suggested that as manyas 40% of P.aeruginosa infections in ICUsmay be acquired from water systems.10

Elizabeth Hospital in Birmingham (QEHB)examined the efficacy of using abenchtop/washer disinfector to removeartificial P. aeruginosa biofilm contaminationfrom the components of a new generationdetachable tap assembly incorporating aTMV. The tap unit investigated was theArmitage Shanks Markwik21 system, whichcan be de-mounted from the wall andcompletely taken apart. This makes it suitableto load into a small washer/disinfector that isalready being used for other equipment. Theresearch actively demonstrates for the firsttime that the Markwik21 tap components canbe decontaminated effectively in a compliantwasher/disinfector.

What are TMVs and why can theybe problematic?TMVs are valves that blend hot water withcold water, providing constant temperaturesto prevent scalding from tap and showeroutlets. This is particularly important forcertain ‘high risk’ patient groups, such aspaediatrics, in non-augmented care locationswhere patients need full body immersion andfor groups such as the very elderly, who mayhave reduced sensitivity to temperature. TheHTM 04-01 Addendum is clear that scaldingrisk assessments should be included in watersafety plans and that TMVs should be fittedwhere the risk assessment shows vulnerablepatients are at risk of scalding. The guidancestates: “a TMV that is integral to the body ofthe tap/shower is preferred, as it is designedto always draw cold water through every timethe outlet is used, thus helping to minimisethe risk of stagnation.”

The use of TMTs is also recommended inthe guidelines for the control of legionella,HSG 274 part 2. These note that type 3thermostatic mixing valves should be fitted towashbasins and sinks in areas with ‘highrisk’ users, “as close as possible to the point-of-use.” In other words, it is preferable thatthey are not positioned behind the IPS panel t

Researchers in France have discoveredthat volatile compounds released by abacterial pathogen stimulate the growth ofa fungal pathogen found in lung infectionsin cystic fibrosis (CF). The findings,published in mBio, an online open-accessjournal of the American Society forMicrobiology, show for the first time thatone pathogen can emit a signal throughthe air that acts as a direct fuel for anotherpathogen to grow.The bacteria Pseudomonas

aeruginosa and the fungus Aspergillusfumigatus are both opportunisticpathogens often found together in the lungmicrobiota. When the two pathogens comeinto direct contact, previous research hasshown that the bacteria producecompounds that inhibit fungal growth.Because microbes often produce volatilecompounds that can travel through the air,Jean-Paul Latgé Christoph, Heddergott andBenoit Briard, members ofthe Aspergillus unit at the Pasteur Institutein Paris, wondered if these two pathogenscould also communicate via volatilesignals.“To our surprise, volatiles produced

by Pseudomonas aeruginosa werepromoting the growth of the Aspergillusfumigatus fungus,” said Latgé. “Even moresurprising, we found that these volatileswere actually taken up by the fungus tosupport growth.”To test how volatile compound signals

might travel between and influence themicrobes, Heddergott and Briard placed asmall Petri dish of Aspergillus to one sideinside a larger Petri dish ofa Pseudomonas culture. Physicallyseparated by the plastic dishes, themicrobes shared common airspace abovethe dishes’ surfaces.“We simply put these two organisms

together and in a couple of days, we weresurprised to see the fungus growing fasterand growing towards the bacteria,” saidHeddergott. “This really indicatedsomething stimulatory [coming from thebacteria].”

New insights into relationship betweenPseudomonas and Aspergillus

To find out what it might be, he usedspecial fibres to absorb the volatilecompounds released from each pathogenand then identified them. Heddergott thentested each of the volatiles producedby Pseudomonas individually on thefungus alone.“The most pungent ones containing

sulfur stimulated the fungus to grow at thesame concentration as co-growing with thebacteria,” said Heddergott. He narrowed itdown to just one airborne compoundmainly responsible for the growth –dimethyl sulfide.Because sulfur is an essential

component that Aspergillus needs forgrowth, the team tested whether dimethylsulfide was actually being taken up andused as food by the fungus. Heddergottand Briard placed the fungus on a plate offood lacking sulfur, then pumped dimethylsulfide into the airspace. They showed thatthe fungus grew better with dimethylsulfide present and sucked the dimethylsulfide directly out of the air as fuel.“Before now, no one thought that a

fungus could grow on volatile compoundsbringing sulfur,” commented Latgé. In thecontext of CF lung infections, Latgé saidthis might explain why the bacteria usuallycolonise lungs first and the funguscolonises later: “When the fungus reachesthe patient’s lung, having bacteria that arereleasing this volatile will help the fungusestablish itself.”Understanding the relationships between

these microorganisms and how theycolonise lungs could lead to better ways toprevent these bacterial-fungal co-infections, which are responsible for acuteworsening of symptoms and declining lungfunction in CF patients.“This opens our eyes to look not at just a

single organism in human infections, butrather a series of microorganisms,”concluded Latgé. “They can be far awayfrom each other, communicating over adistance, and even using volatilecompounds produced by another microbeto grow.”

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contamination has been well documented.Biofilm grows best in stagnant water,

such as in dead legs caused by alterations to pipe work or due to under-used outlets,generally in warm temperatures between 20 and 50˚C. These temperatures areparticularly favourable to the growth oflegionella bacteria. Other favourableconditions include certain types of materials,such as polymers and rubbers used insidetaps and flexible hoses, and the presence ofnutrients, such as rust from corroded metalsfound in old pipe work. In hard water areas,

limescale build-up can encourage biofilmgrowth, particularly on aerators and flowstraighteners in tap outlets, and it was thesethat were found to be the culprits in theneonatal deaths in Belfast.

TMTs can be problematical if they have a complicated tap design because thenumerous surfaces inside their TMVs can beconducive to biofilm growth. They may alsoutilise materials, such as those mentionedabove, that promote biofilm, and internalwater chambers can cause relatively staticreservoirs of stagnant water that may be

vulnerable to biofilm formation and legionellaproliferation. Biofilm containing P. aeruginosais most likely to occur at the tap and the lasttwo metres of pipe work, unlike legionella-containing biofilm, which usually sits at theheart of a water system. In healthcarefacilities, water needs to be circulated to thepoint of use at temperatures above 50˚C as aprimary control method to kill legionella –hence the need for TMVs to prevent scalding.

Other control methods include regularflushing of outlets, which is key inprevention of stagnation, and robust dailycleaning carried out correctly to prevent crosscontamination, which should prevent build-up of scale deposits on tap outlets.

New decontamination dataThe test bacteria used in the HIRL researchwere the P. aeruginosa NCTC 6749disinfection test strain and a P. aeruginosaPS-1054 isolate from QEHB known toproduce biofilm. The Markwik21 taps testedhave a demountable body, a detachablespout, an integral TMV and a patented‘BioGuard’ outlet, constructed from brasswith a copper lining, which is naturally anti-microbial to discourage the attachment ofbiofilm. All the components can withstandvery high temperatures and are compliantwith the HTM 04-01 Addendum.

The tap spout, TMV and pipe work wereflushed and immersed in a sterile watersuspension of the test bacteria, at aconcentration of around 108/ml. Thecomponents were sealed in a plastic bag, tokeep surfaces moist, and left for seven daysto allow enough growth to imitate in-useconditions. The components – the spout,including the BioGuard outlet, mixing valveand pipe – were then processed in aMedisafe Pico thermal washer/disinfector,which is compliant with EN 15883 Part 1.This washer/disinfector was programmed todisinfect at >80˚C for ten minutes and thetap assembly was loaded in a standardmanner. The wash fluid used was Medisafe’s3E-Zyme, which uses a combination of threeph neutral, non-corrosive “high performance”enzymes.

All the components tested were sampledand cultured before and after disinfection toestablish pre- and post-disinfection countsand the wash fluid was also cultured todetermine the number of viable bacteria.

The number of colony forming units fromthe cultures, as counts per 100ml ofsampling fluid, were converted to the log10

system from which the log10 reductions werecalculated. Three test cycles were carried out.

Compliance with EN standards requires a> 5 log10 reduction in test bacteria

3 in orderto comply with EN standards for chemicaldisinfectants so this reduction was used inthis context as an indicator for effectivedisinfection. The data produced by the studyindicated an A0 value of 600 or disinfectionat 80˚C for ten minutes. A > 5 log10 inP.aeruginosa was achieved. Thisdemonstrated that the Markwik21 tap

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components were effectively decontaminatedin a compliant washer/disinfector. Thestudy’s authors noted: “the advantage ofprocessing in a washer/disinfector is thatcleaning [forms] part of the cycle that willassist with removal of possible biofilm.”

Because the decontamination protocoltested at Birmingham’s QEHB has not beenused before in the UK, the results provide asignificant new option for infection controlteams that want to retain these particularTMTs.

TMTs in practiceThe Belfast 2012 Belfast neonatal incidenthas prompted some Trusts to review theirwater outlets, making the decision to moveaway from flow restricted and aerated tapends while retaining integral TMVs. Anumber of them have switched the tapoutlets in their clinical areas to Markwik21detachable manual TMTs with ‘straightthrough’ BioGuard outlets.

In addition, if a pseudomonas count isdetected the outlet can be replaced with anew one. The removed outlet can then bechlorinated and de-scaled so it becomesavailable to use at another location. If theproblem persists after re-testing of a cleanreplacement, the entire tap can be removed.

While it would be rare for a Trust to usepoint-of-use (POU) filters if they have thecapacity to replace tap components easily,certain systems are compatible with POUfilters – eg the Markwik21 system is now

compatible with Pall Medical POU filters –providing an emergency solution fororganisations that may have fewer tapreplacements available. CSJ

Susan Pearson BSc is a freelance journalistand communications consultant specialisingin medicine and the environment. She writesregularly about water microbiology.

References1 https://www.gov.uk/government/uploads/system/

uploads/attachment_data/file/140105/Health_Technical_Memorandum_04-01_Addendum.pdf

2 HSG 274 Part 2: www.hse.gov.uk/pUbns/

priced/hsg274part2.pdf 3 EN 15883: Washer disinfectors: Part 1 General

requirements, terms and definitions and tests,2006.

4 J.-L. Vincent et al, JAMA, 274(8): 639-644, 1995.5 Melsen W.G. et al, Crit Care Med, 39: 1-7, 2011.6 Levin, M.H. et al, J Clin Pathol 37:424-427, 1984.7 Grundmann H et al J Infect Diseases 168: 943-

947, 1993.8 Valles, J. et al Intensive Care Med, 30: 1768-1775,

2004. 9 Rogues, A. et al J Hosp Infect, 67: 72-78, 2007.10 Exner, M. ‘Tap Water’, European Hospital, 8 July,

2010: http://www.european-hospital.com/en/article/335-Tap_water.html