Environmental CRO Contamination in New Hospital Buildings – What to do about the waste water interface?

How long does it take for multi-drug resistant organisms to take up residence within environmental reservoirs and niches of newly built healthcare facilities?  Sadly this may be before building handover, or relatively shortly after first patient occupation.  The origin and timings of such environmental colonisation is not clear cut, however, there have been a number of recent publications which support Water Safety Groups when planning and working on new build projects.

The team from Duke University School of Medicine, North Carolina, USA (Warren et al) undertook a prospective observational study of the timing, rate and frequency of carbapenem-resistant organisms (CRO) colonisation of patient room handwashing basins in two neurological ICUs (A & B) of a newly constructed hospital. 

All 26 single-patient rooms in each of the ICUs had clinical handwash basins.  Unit A was opened to patient admissions in July 2020, and the first monthly study samples were taken in September 2020 through to May 2021.  Unit A patients were moved to Unit B in June 2021, with monthly study samples taken for a further 12 month period.  Microbiological samples were taken from the top of the handwash basin bowl (horizontal surface swab), the drain interface (swab) and the Ubend (liquid sample) in each of the patient rooms.  All patients were screened weekly via rectal swabs for carbapenem-resistant enterobacteria (CRE).

In total, 2814 patients were admitted during the study, with only n=2 patients identified as CRE positive (Klebsiella pneumoniae carbapenemase-producing isolates) who were both housed within ICU A.

Approximately 15% of sinks in ICU A were already contaminated with CRO within 60 days of opening to patient admission, with 35% contaminated by month 10.  In ICU B all samples obtained prior to patient admission were negative for CRO, but 100% of sinks were contaminated by month 7 post occupation.  Notably, the 2 patients identified as colonized with CRE were in rooms 30 days prior to a sink contamination event.

Of the CROs recovered from sinks,  Enterobacter cloacae (n=151; 51%) and Pseudomonas aeruginosa (n=102; 34%) were the most common.  Despite enhanced room cleaning (including UVC light disinfection) following patient discharge, the ubend remained persistently positive.  It was necessary to replace the ubend with a new component and use a physical clean, detergent and a chlorine shock dose on the remaining pipework in order to clear the colonisation.

Warren’s paper is not in isolation.  Another prospective study, this time by van der Schoor and the Rotterdam team, followed levels of environmental contamination in their old building (built in 1961 with mainly multiple-occupancy rooms) and their new hospital building (built in 2018 with 100% single-occupancy rooms).   Whilst the new hospital had fewer highly resistant microorganisms present, they were all (100%) found in the patient ensuite bathroom.  The transition to 100% single occupancy rooms gave many benefits from an infection prevention perspective and allowed an enhanced final clean between patient admission.  However a routine of bathing patients with pre-packed washcloths rather than water and cleanser due to the risk of microorganism transmission both to the patient and to the sink was maintained in both the old and the new hospital.

The German team (Boutin et al) prospectively followed their new build environment from one month prior to opening for patient admission to 12 months post occupation.  They reported environmental colonisation of toilets and handwash basin drains in their surgical ICUs, and the time lapse to contamination, with carbapenem-resistant Gram negatives (CRGN).  Patients were screened at admission and then weekly for CRGN via rectal swab. 

Twenty-nine isolates were found in patients with 52 isolates from the environment – mainly (71%) from sink drains.  The team only found 2 patients who shared a clone that could have been transmitted person-to-person.  The remaining transfer was considered to come from the contaminated wastewater system interface. Pseudomonas aeruginosa and Enterobacteriales were the two most common patient and environmental CRGN isolates.  The time taken to colonise sinks and toilets was 5 months post patient occupancy.  The authors concluded that “…the most common origin of persistent environmental contamination is the patients themselves.”

These publications remind us that the presence of CRO at hospital handwash basins, showers and toilets should be expected, and that this poses a risk to those in close proximity whenever basin is in use.  Disposal of body fluids, IV fluids and TPN into the waste water system provides nutrients and encourages amplification of contamination.  Any slow flow or blockage in the waste water system can lead to the spread of microorganisms into nearby ubends, sometimes even refluxing into shower trays and basins.  It is vital that any blockage reports are responded to urgently in order to reduce the risk of microorganism transmission.

It is critical for Water Safety Groups to recognise the risk to patient safety from the presence of water sources, and the most effective measure to prevent transmission is to remove the water source altogether.  If removal is not possible, then strategies to mitigate contamination of surfaces surrounding handwash basins and showers (such as splash screens and 2 meter clear zones) should be implemented.  Where there is persistent contamination of tap outlets there should be consideration that such contamination is coming from the drain.  Remediation may mean replacing the ubend and pipe leading to the drain as evidence suggests disinfection is ineffective with very short term impact.  Verify the effectiveness and sustainability of such remediation.

Molecular and metagenomic testing techniques provide much clearer, more robust and detailed information than culture methods and should support better environmental surveillance of water sources, particularly where there is an outbreak or suspected outbreak of Gram negative infections or increased surveillance during commissioning, handover and the early months of building occupation.

We hope these papers will be of interest to Water Safety Groups in the handover and early patient occupation phases of new build or refurbishment projects, and for support around heightened patient and environmental surveillance during the first year of steady state operation.  If you would like to discuss this information, your new build project or commissioning plan further, please contact us


Warren BG, Smith BA, Barrett A, Graves AM, Nelson A, Gettler E, Lewis SS, Anderson DJ. Identification of carbapenem-resistant organism (CRO) contamination of in-room sinks in intensive care units in a new hospital bed tower. Infect Control Hosp Epidemiol. 2024 Mar;45(3):302-309. doi: 10.1017/ice.2023.289. Epub 2024 Jan 19. PMID: 38239018; PMCID: PMC10933507.

van der Schoor AS, Severin JA, Klaassen CHW, Gommers D, Bruno MJ, Hendriks JM, Voor In ‘t Holt AF, Vos MC. Environmental contamination with highly resistant microorganisms after relocating to a new hospital building with 100% single-occupancy rooms: A prospective observational before-and-after study with a three-year follow-up. Int J Hyg Environ Health. 2023 Mar;248:114106. doi: 10.1016/j.ijheh.2022.114106. Epub 2023 Jan 6. PMID: 36621268.

Boutin S, Scherrer M, Späth I, Kocer K, Heeg K, Nurjadi D. Cross-contamination of carbapenem-resistant Gram-negative bacteria between patients and the hospital environment in the first year of a newly built surgical ward. J Hosp Infect. 2024 Feb;144:118-127. doi: 10.1016/j.jhin.2023.11.016. Epub 2023 Dec 9. PMID: 38081456.

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