Multi-Drug Resistant Microorganisms In Your Drains

Evidence linking the role of water services – both potable influent and waste waters – in the transmission of waterborne pathogens such as Legionella pneumophila, Pseudomonas aeruginosa, Non-tuberculous Mycobacteria and their resulting infections has increased significantly in recent years.  The reported in-premise multi-drug resistant waterborne infections such as from Pseudomonas aeruginosa, P. putida, Klebsiella pneumoniae, K. oxytoca, Escherichia coli and Enterobacter cloacae have been particularly alarming in the last decade.  However it must be recognised that the use of finicky plate culture techniques to assess contamination in water samples and the lack of routine sampling from drains during standard environmental surveillance means that the infectious link between sensitive microorganism strains (often leading to “background” patient infections) from water services is missed.

In a recent Blog ( we have highlighted the water system periphery (the 2 meter zone before and after a water outlet) and as being a significant source of waterborne infections.   Wastewater drains are featuring more frequently in our working experiences with infectious event investigation, environmental surveillance and with dynamic Water Safety Groups within healthcare facilities who keenly follow the latest publications, explore and adopt best practice.  Infection prevention in the built environment remains somewhat blinkered when it comes to the water pouring from our taps and showers; there is a false sense of security and an assumption that it is “safe”.

What could possibly go wrong?

There are many reasons why sink and shower drains represent the perfect storm as an environmental niche for multi-drug resistant pathogens.

By design wastewater drains are rich environments for the amplification of microorganisms and the formation of biofilms, and it is important to recognise in a hazard/risk assessment that pathogens can grow from the U-Bend towards the sink at a rate of 2.5 cm per day (Kotay et al., 2017).  Drains interface with the sink/basin bowl, the tail drain pipe connects to the U-Bend which contains water to prevent escape of sewer gases. Access for effective routine cleaning and disinfection is near impossible and frequent access is inappropriate in patient areas with the necessary subsequent room decontamination required following such intervention.

Points to consider as a Water Safety Group are:

  • Materials of drain construction – typically plastic (polypropylene) – attractive for biofilm formation and the microorganism genetic exchange that occurs within it
  • Design – blockage, back-up, slow drainage.  Inter-sink transfer of multi-resistant pathogens has been shown following back-flow (Aranega-Bou et al., 2021)
  • Throughput of hot, tepid and cold fluid temperatures, with long periods stagnating at ambient room temperature
  • Inaccessibility of drain componentry (including behind panels), and restricted logistics as it is inappropriate to work on drains whilst patient areas are in use
  • Plumes of aerosols from disturbed water filled U-Bends enter the user interface at the sink, basin or shower.  Often patient bedspaces or clinical materials /surfaces are within 2 meters of the drain
  • Often very vulnerable users are exposed
  • Poor user behaviour (staff, visitor and patient) through inappropriate cleaning, disposal of non-compliant fluids (including residual volumes of IV antibiotics and parenteral nutrition), disposal of non-compliant objects (solid items frequently found in U-Bends), stagnancy from lack of consistent multi-daily usage
  • No effective guidance or protocols for appropriate cleaning, operational monitoring, sampling, testing, control measures or remediation for drains
  • Lack of support for removing water services from patient areas, despite significant evidence linking waterborne infection to vulnerable users. 
  • Inadequate risk assessment for the installation of handwash basins and other water services
  • Repeated exposure of biofilms to sublethal and ineffective disinfectants/biocides without any physical cleaning to disrupt biofilms

Evidence linking infections to the drain

A literature review targeting the last 5 years of accessible publications reveals a plethora of independent publications on contaminated drains.  A selection has been summarised below for convenience and to give an overview of problems encountered, the respective authors’ experiences and conclusions.

Author & DateSummary
Jung et al., 2020Report on a carbapenemase-producing Enterobacteriaceae (CPE) outbreak involving 87 patients over a 6 month period in Cardiac Intensive Care Units.  Using sinks within patient rooms and bathrooms for brushing teeth was associated with CPE acquisition, as was drinking from water supplied via a dispenser.  Pulsed-field gel electrophoresis analysis linked the infectious strain in patients, water dispenser and patient sink drains
Volling et al., 2020Literature review assessing evidence for transmission of antimicrobial-resistant organisms from sink drainage systems, in particular hospital-acquired Gammaproteobacteria.  52 studies implicating sink drainage systems in acute care hospitals were identified which provided evidence of co-occurrence of contaminated sink drainage systems and colonization/infection, temporal sequencing compatible with sink drainage reservoirs, some steps in potential causal pathways, and relatedness between bacteria from sink drainage systems and patients. Some studies provided convincing evidence of reduced risk of organism acquisition following interventions
Inkster et al., 2021An outbreak of Cupravidus pauculus in a newly built hospital’s paediatric haemato-oncology unit.  Widespread contamination of the water and drainage system was found. Drains were found to have underlying structural problems
Constantinides et al., 2020The authors demonstrated that hospital sink drains are abundantly and persistently colonised with diverse populations of Escherichia coli, Klebsiella pneumoniae and Klebsiella oxytoca, including resistant and susceptible strains.  Populations were structured by ward and sink with only a few lineages indicating selection pressures.  The authors suggest that sinks may contribute up to 10% of infections caused by these organisms on the ward
Nurjadi et al., 2021The authors characterised 133 clinical and environmental OXA-48-producing Enterobacter cloacae isolates through Whole Genome Sequencing as part of an investigation of a prolonged and intermittent outbreak involving 41 haematological patients.  There was strong evidence to suggest that showering was the most likely route of acquisition.  In 20/38 (53%) patient rooms the wastewater traps and drains were contaminated.  Decontamination using 25% acetic acid three times per week was effective in reducing positivity, but not in reducing new infections.  An engineering solution of removable and autoclavable custom-made shower tray inserts did prevent new infections by blocking access to the drain 
Carling, P.  2018A review of 23 carbapenem-resistant-organism outbreaks which were linked to wastewater drains.  Important characteristics noted were: a) long duration of outbreaks (average 37 months)  b) low frequency of infectious events (average 10 months between cases) c) high prevalence of sink colonisation with the outbreak strain  d) extremely difficult to mitigate/resolve
Jamal et al., 2020The presence of CPE in sink /shower drains was confirmed in 70% (7/10) hospitals under investigation, with 53/1209 (4%) drains returning positive results.  Four of these contaminated drains were linked to infected patients via whole genome sequencing.  Analysis revealed that shower drains were most likely to be contaminated vs hand hygiene drains vs patient-use handwash basins (least likely to be contaminated).  Data also revealed drain-to-drain contamination, confirming the importance of slow flow/blockage on presence and spread of resistant organisms
Kizny-Gordon et al., 2017Increasing reports of carbapenem-resistant organisms in the hospital water environment with drains, sinks and taps most frequently colonised and Pseudomonas aeruginosa the most predominant resistant organism.  Only one third of outbreaks were successfully resolved through eliminating the organism from the water environment.  Replacement of colonised components and reservoirs may be required for long term success
Hopman et al., 2019Investigation of 11 infected patients led to the plausible transmission of carbapenemase-producing Pseudomonas aeruginosa from the hospital environment to the patient via aerosols generated from contaminated shower drains, sink and an air sample from patient rooms.  Confirmation of patient and environmental strain was by whole-genome sequencing.  Rethinking the hospital-built environment, including shower drains and the sewage system, will be crucial for the prevention of severe hospital-acquired infections
van der Zwet et al., 20222 outbreaks caused by identical Enterobacter cloacae and Pseudomonas putida were detected in 15 and 9 haematology-oncology patients respectively. Both species were highly antibiotic resistant.  Despite intensified infection control measures, new cases were found weekly.  Environmental samples from sinks and shower drains were positive in 18% of samples.  All sink U-bends were replaced, and disinfection of sink and shower drains was completed using chlorine and soda on a daily basis to control the outbreak strains
Walker et al., 2023Review of published literature and including the authors experiences of problems and challenges associated with water and wastewater systems in intensive care settings.  Multiple issues were described, many of which result from lack of input at the architectural design and specification stage.  This leads to patients and staff being put at risk for the life of the installation.  The problems with misuse of hand hygiene stations and the presence of wastewater drain systems within the intensive care area must be addressed if vulnerable patients are to be safeguarded
Weinbren et al., 2023Transmission of waterborne pathogens and rates of infection in intensive care patients are increasing and sustainable approaches to mitigate these problems are rare.  The rise of “water-free” care, combined with the removal of water services from vulnerable patient areas has seen significant improvements and future design should consider such approach. Interim measures for existing units need careful evaluation and guidance

What is the solution?

The built environment is a source for infectious outbreaks and sporadic transmission events of waterborne pathogens to water system users.  The importance of sink drains as reservoirs of pathogens is being recognised and potential interventions to reduce contamination within drains and on surfaces surrounding sinks are being sought.  Re-engineered sink designs have shown some promising support data (Cole et al., 2019), however the importance of design, materials specification, commissioning, daily operational controls, user behaviour and environmental surveillance need considerable improvement.  There must be greater awareness of the responsibility that surrounds having a water source and drain installed.  Every installation must be considered a hazard.

Do not passively rely on Guidance to base decisions regarding in-premise water safety; it is mostly outdated and not holistic, and more importantly ineffective.  We urge the regular review of newly published independent data, assess gaps and implement improvements which can be validated and verified within your own premises.  Read the latest publications in the Journal of Infection Prevention from three talented and experienced “waterborne” and “ventilation” experts – Jimmy Walker, Michael Weinbren and Teresa Inkster – which inspires action (Journal of Infection Prevention, Volume 24, Issue 2, March 2023.  Pages 55-59, 60-64, 65-70).  In our opinion, here lies effective best practice and future guidance.

Harper Water Management Group have considerable experience in mitigating critical contamination and outbreaks from the influent potable water system through to waste water drainage.  It is paramount to engineer the problem out and work as a multi-disciplinary team to achieve a sustainable result, otherwise intermittent and prolonged infectious outbreaks will not be resolved.  Please let us know if you and your Water Safety Group would like to discuss this serious subject matter further.

References & Further Reading

Aranega-Bou P, Ellaby N, Ellington MJ, Moore G. Migration of Escherichia coli and Klebsiella pneumoniae Carbapenemase (KPC)-Producing Enterobacter cloacae through Wastewater Pipework and Establishment in Hospital Sink Waste Traps in a Laboratory Model System. Microorganisms. 2021 Sep 3;9(9):1868. doi: 10.3390/microorganisms9091868. PMID: 34576763; PMCID: PMC8468231.

Carling PC. Wastewater drains: epidemiology and interventions in 23 carbapenem-resistant organism outbreaks. Infect Control Hosp Epidemiol. 2018 Aug;39(8):972-979. doi: 10.1017/ice.2018.138. Epub 2018 Jun 28. PMID: 29950189.

Constantinides B, Chau KK, Quan TP, Rodger G, Andersson MI, Jeffery K, Lipworth S, Gweon HS, Peniket A, Pike G, Millo J, Byukusenge M, Holdaway M, Gibbons C, Mathers AJ, Crook DW, Peto TEA, Walker AS, Stoesser N. Genomic surveillance of Escherichia coli and Klebsiella spp. in hospital sink drains and patients. Microb Genom. 2020 Jul;6(7):mgen000391. doi: 10.1099/mgen.0.000391. PMID: 32553019; PMCID: PMC7478627.

Cole K, Talmadge JE. Mitigation of microbial contamination from waste water and aerosolization by sink design. J Hosp Infect. 2019 Oct;103(2):193-199. doi: 10.1016/j.jhin.2019.05.011. Epub 2019 May 28. PMID: 31145930.

Hopman J, Meijer C, Kenters N, Coolen JPM, Ghamati MR, Mehtar S, van Crevel R, Morshuis WJ, Verhagen AFTM, van den Heuvel MM, Voss A, Wertheim HFL. Risk Assessment After a Severe Hospital-Acquired Infection Associated With Carbapenemase-Producing Pseudomonas aeruginosa. JAMA Netw Open. 2019 Feb 1;2(2):e187665. doi: 10.1001/jamanetworkopen.2018.7665. PMID: 30768189; PMCID: PMC6484879.

Inkster T, Peters C, Wafer T, Holloway D, Makin T. Investigation and control of an outbreak due to a contaminated hospital water system, identified following a rare case of Cupriavidus pauculus bacteraemia. J Hosp Infect. 2021 May;111:53-64. doi: 10.1016/j.jhin.2021.02.001. PMID: 33926650.

Jamal AJ, Mataseje LF, Brown KA, Katz K, Johnstone J, Muller MP, Allen VG, Borgia S, Boyd DA, Ciccotelli W, Delibasic K, Fisman DN, Khan N, Leis JA, Li AX, Mehta M, Ng W, Pantelidis R, Paterson A, Pikula G, Sawicki R, Schmidt S, Souto R, Tang L, Thomas C, McGeer AJ, Mulvey MR. Carbapenemase-producing Enterobacterales in hospital drains in Southern Ontario, Canada. J Hosp Infect. 2020 Dec;106(4):820-827. doi: 10.1016/j.jhin.2020.09.007. Epub 2020 Sep 9. PMID: 32916210.

Jung J, Choi HS, Lee JY, Ryu SH, Kim SK, Hong MJ, Kwak SH, Kim HJ, Lee MS, Sung H, Kim MN, Kim SH. Outbreak of carbapenemase-producing Enterobacteriaceae associated with a contaminated water dispenser and sink drains in the cardiology units of a Korean hospital. J Hosp Infect. 2020 Apr;104(4):476-483. doi: 10.1016/j.jhin.2019.11.015. Epub 2019 Nov 27. PMID: 31785319.

Kizny Gordon AE, Mathers AJ, Cheong EYL, Gottlieb T, Kotay S, Walker AS, Peto TEA, Crook DW, Stoesser N. The Hospital Water Environment as a Reservoir for Carbapenem-Resistant Organisms Causing Hospital-Acquired Infections-A Systematic Review of the Literature. Clin Infect Dis. 2017 May 15;64(10):1435-1444. doi: 10.1093/cid/cix132. Erratum in: Clin Infect Dis. 2017 Oct 15;65(8):1431-1433. PMID: 28200000.

Kotay, S, Chai, W, Guilford, W, Barry, K, Mathers, AJ. Spread from the sink to the patient: in situ study using green fluorescent protein (GFP)-expressing Escherichia coli to model bacterial dispersion from hand-washing sink-trap reservoirs. Appl Environ Microbiol 2017;83(8): pii: e03327–

Nurjadi D, Scherrer M, Frank U, Mutters NT, Heininger A, Späth I, Eichel VM, Jabs J, Probst K, Müller-Tidow C, Brandt J, Heeg K, Boutin S. Genomic Investigation and Successful Containment of an Intermittent Common Source Outbreak of OXA-48-Producing Enterobacter cloacae Related to Hospital Shower Drains. Microbiol Spectr. 2021 Dec 22;9(3):e0138021. doi: 10.1128/Spectrum.01380-21. Epub 2021 Nov 24. PMID: 34817232; PMCID: PMC8612159.

Volling C, Ahangari N, Bartoszko JJ, Coleman BL, Garcia-Jeldes F, Jamal AJ, Johnstone J, Kandel C, Kohler P, Maltezou HC, Maze Dit Mieusement L, McKenzie N, Mertz D, Monod A, Saeed S, Shea B, Stuart RL, Thomas S, Uleryk E, McGeer A. Are Sink Drainage Systems a Reservoir for Hospital-Acquired Gammaproteobacteria Colonization and Infection? A Systematic Review. Open Forum Infect Dis. 2020 Dec 8;8(2):ofaa590. doi: 10.1093/ofid/ofaa590. PMID: 33553469; PMCID: PMC7856333

Walker J, Inkster T, Weinbren M. Aspects and problems associated with the water services to be considered in intensive care units. J Infect Prev. 2023 Mar;24(2):60-64. doi: 10.1177/17571774231152716. Epub 2023 Jan 12. PMID: 36815062; PMCID: PMC9940243.

Weinbren M, Inkster T, Lafferty F. Drains and the periphery of the water system – what do you do when the guidance is outdated? Infect Prev Pract. 2021 Oct 20;3(4):100179. doi: 10.1016/j.infpip.2021.100179. PMID: 34988421; PMCID: PMC8696270.

Weinbren M, Inkster T, Walker J. Implementing changes to reduce infections in ICU patients. Water services and waste systems. Journal of Infection Prevention. 2023;24(2):65-70. doi:10.1177/17571774231152715

van der Zwet WC, Nijsen IEJ, Jamin C, van Alphen LB, von Wintersdorff CJH, Demandt AMP, Savelkoul PHM. Role of the environment in transmission of Gram-negative bacteria in two consecutive outbreaks in a haematology-oncology department. Infect Prev Pract. 2022 Feb 25;4(2):100209. doi: 10.1016/j.infpip.2022.100209. PMID: 35295671; PMCID: PMC8918851.

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