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Scientific literature · Verified citations

Research on
drains.

Twelve peer-reviewed papers on drains as a pathway for infection, odour and gas in healthcare, hospitality and food service. Each one comes with a note on what it does not show.

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12
Peer-reviewed papers
4
Themes
0
Papers about Green Drain
2004–2025
Year range
Introduction

What this library is, and what it is not.

This is a list of peer-reviewed scientific papers on drains as a route for infection, odour and sewer gas. Every citation on this page — authors, year, title and journal — has been verified independently against an abstract or a publisher page. The summaries are our own.

None of these papers tested Green Drain and none of them endorses it. No product of any kind is named in them. They document the risk the product addresses — that is the whole of our claim, and the whole of what may legitimately be read into them.

For each paper we deliberately record what it does not show. Most of this research was carried out in laboratory models, using surrogate organisms, and measures colonisation rather than infection. Several of the papers directly contradict claims that are routinely repeated in the marketing of this product category. They are here precisely for that reason.

If you are looking for test data on the product itself — flow, pressure, aerosol retention, durability — that lives on a separate page.

The drain as a reservoir

The sink, the trap and the way out

This group is about a single drain: what lives in it, how it gets out and how far it reaches. Two of the three papers here actually narrow the aerosol claim — which is precisely why they are worth reading.

01

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

Kotay S, Chai W, Guilford W, Barry K, Mathers AJ · 2017 · Applied and Environmental Microbiology

In a purpose-built hand-washing sink gallery, the authors seeded GFP-labelled E. coli into the P-trap and found that running the tap did not disperse the organism to the basin or countertop. Only after about seven days, once the organism had grown as a biofilm up the drain pipe to the strainer, did tap flow throw contaminated droplets onto the basin and the surrounding surfaces. The study also showed that neighbouring sinks connected by shared wastewater plumbing could contaminate one another.

What it does not show

This is a laboratory model using a harmless surrogate organism. It records no patient infections, no attack rates and no measure of real-world risk. It argues against the idea that bacteria simply float up out of standing trap water — the biofilm first had to physically reach the strainer.

Citation

Kotay S, Chai W, Guilford W, Barry K, Mathers AJ (2017). “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.” Applied and Environmental Microbiology 83(8):e03327-16. doi:10.1128/AEM.03327-16 · PMID 28235877

02

Droplet- Rather than Aerosol-Mediated Dispersion Is the Primary Mechanism of Bacterial Transmission from Contaminated Hand-Washing Sink Traps

Kotay SM, Donlan RM, Ganim C, Barry K, Christensen BE, Mathers AJ · 2019 · Applied and Environmental Microbiology

Using settle plates and air sampling on replicate sinks, the same group measured when bacteria actually leave a contaminated trap. Organisms were recovered only during tap events, never before them, between them or without them, and recovered counts fell sharply within thirty minutes of the tap being used. The authors conclude that transmission travels on comparatively large droplets that settle quickly rather than on a persistent airborne aerosol.

What it does not show

This paper narrows, rather than widens, the claim. It is evidence against a continuous aerosol plume rising from a hand-washing sink trap, and it says nothing about floor drains, about pressure-driven events in the drainage stack, or about infection in patients.

Citation

Kotay SM, Donlan RM, Ganim C, Barry K, Christensen BE, Mathers AJ (2019). “Droplet- Rather than Aerosol-Mediated Dispersion Is the Primary Mechanism of Bacterial Transmission from Contaminated Hand-Washing Sink Traps.” Applied and Environmental Microbiology 85(2):e01997-18. doi:10.1128/AEM.01997-18 · PMID 30367005

03

Carbapenem-resistant Enterobacteriaceae dispersal from sinks is linked to drain position and drainage rates in a laboratory model system

Aranega-Bou P, George RP, Verlander NQ, Paton S, Bennett A, Moore G; TRACE Investigators' Group · 2019 · Journal of Hospital Infection

A laboratory sink model with hospital-derived and inoculated waste traps measured how far carbapenem-resistant Enterobacteriaceae travel out of a sink. Significantly fewer bacteria were dispersed from fast-draining sinks and from sinks whose drain sits at the rear rather than directly under the tap; with slow drainage, a rear-draining sink dispersed roughly thirty times less than one with the drain under the tap. Contaminated splashes were recovered up to a metre from the sink.

What it does not show

A model system, not a ward. It quantifies dispersal distance and the effect of basin geometry, not infection risk, and it does not establish that any patient was ever infected by this route.

Citation

Aranega-Bou P, George RP, Verlander NQ, Paton S, Bennett A, Moore G; TRACE Investigators' Group (2019). “Carbapenem-resistant Enterobacteriaceae dispersal from sinks is linked to drain position and drainage rates in a laboratory model system.” Journal of Hospital Infection 102(1):63–69. doi:10.1016/j.jhin.2018.12.007 · PMID 30571992

Outbreaks and interventions

What happened in hospitals

These are hospital data: outbreaks that ran for years, measures that worked and measures that did not. None of these papers tests a floor-drain seal.

04

Wastewater drains: epidemiology and interventions in 23 carbapenem-resistant organism outbreaks

Carling PC · 2018 · Infection Control & Hospital Epidemiology

A single-author review that gathers published hospital outbreaks attributed to wastewater drains, selected where the report investigated the epidemiology of drain-associated transmission, used genomic or molecular methods to establish clonality, or described a mitigation intervention. Its premise is that genomic epidemiology combined with a better understanding of drain biofilm ecology has clarified how sink and shower drains contribute to healthcare-associated infection.

What it does not show

This is a narrative review of already-published outbreaks, not primary research and not a meta-analysis. It carries the publication bias of the outbreak literature, cannot establish incidence or causation, and the widely circulated claims that it proves drain biofilm is impossible to eradicate are not supported by its abstract.

Citation

Carling PC (2018). “Wastewater drains: epidemiology and interventions in 23 carbapenem-resistant organism outbreaks.” Infection Control & Hospital Epidemiology 39(8):972–979. doi:10.1017/ice.2018.138 · PMID 29950189

05

A Large, Refractory Nosocomial Outbreak of Klebsiella pneumoniae Carbapenemase-Producing Escherichia coli Demonstrates Carbapenemase Gene Outbreaks Involving Sink Sites Require Novel Approaches to Infection Control

Decraene V, Phan HTT, George R, Wyllie DH, Akinremi O, Aiken Z, et al.; TRACE Investigators' Group · 2018 · Antimicrobial Agents and Chemotherapy

Eight years of linked microbiology and admissions data from a Manchester NHS trust, with 268 sequenced KPC-producing E. coli isolates and more than 184,000 rectal screens, traced an outbreak clone spreading between patients and the environment on two cardiac wards despite cohorting, screening and enhanced cleaning. Acquisition fell after those wards were closed and the plumbing replaced, but the wastewater sites were rapidly recolonised and patient acquisitions recurred, though at a lower rate. The carbapenemase plasmids were also found to have moved into other lineages and species.

What it does not show

An observational outbreak investigation, not a controlled trial; the effect of replacing the plumbing is inferred from time trends and is confounded by the simultaneous ward closure and patient relocation. Read honestly, it is partly a negative result: replacing the pipework did not durably solve the problem.

Citation

Decraene V, Phan HTT, George R, Wyllie DH, Akinremi O, Aiken Z, et al.; TRACE Investigators' Group (2018). “A Large, Refractory Nosocomial Outbreak of Klebsiella pneumoniae Carbapenemase-Producing Escherichia coli Demonstrates Carbapenemase Gene Outbreaks Involving Sink Sites Require Novel Approaches to Infection Control.” Antimicrobial Agents and Chemotherapy 62(12):e01689-18. doi:10.1128/AAC.01689-18 · PMID 30249685

06

Effects of a disinfection device on colonization of sink drains and patients during a prolonged outbreak of multidrug-resistant Pseudomonas aeruginosa in an intensive care unit

de Jonge E, de Boer MGJ, van Essen EHR, Dogterom-Ballering HCM, Veldkamp KE · 2019 · Journal of Hospital Infection

During a clonal multidrug-resistant Pseudomonas aeruginosa outbreak in a Dutch intensive care unit, the siphons in one subunit were replaced with devices that disinfect draining fluid by heat and vibration, while another subunit received new plain PVC siphons as a control. Drain colonisation in the intervention unit fell from 51% to 5%, while the control unit stood at 62%; after the second unit also received devices, colonisation was 8.0% and 2.4%. Patient colonisation fell from 8.3 to 0 per 1000 admissions in the first unit.

What it does not show

A single-centre, non-randomised before-and-after study reporting colonisation, not infection or mortality. The patient-colonisation fall in the second unit was not statistically significant. Note also what the control arm shows: fitting new clean PVC siphons on its own did not control colonisation.

Citation

de Jonge E, de Boer MGJ, van Essen EHR, Dogterom-Ballering HCM, Veldkamp KE (2019). “Effects of a disinfection device on colonization of sink drains and patients during a prolonged outbreak of multidrug-resistant Pseudomonas aeruginosa in an intensive care unit.” Journal of Hospital Infection 102(1):70–74. doi:10.1016/j.jhin.2019.01.003 · PMID 30639071

07

Reduced rate of intensive care unit acquired gram-negative bacilli after removal of sinks and introduction of 'water-free' patient care

Hopman J, Tostmann A, Wertheim H, Bos M, Kolwijck E, Akkermans R, et al. · 2017 · Antimicrobial Resistance and Infection Control

A two-year before-and-after study across five intensive care units of a Dutch tertiary hospital, covering roughly 2,900 patients, removed sinks from patient rooms and introduced a water-free patient-care protocol. Gram-negative bacilli colonisation fell immediately from 26.3 to 21.6 per 1000 ICU admission days (rate ratio 0.82, 95% CI 0.67–0.99). The effect grew with length of stay, reaching a 2.5-fold reduction in patients staying ten days or more.

What it does not show

Not randomised and not blinded, and carried out at one institution where all patients received selective digestive decontamination. The outcome measured is colonisation, not infection or death, and the intervention was a bundle — the contribution of removing the sink cannot be separated from the rest of the protocol. The headline effect is modest, with the confidence interval reaching 0.99.

Citation

Hopman J, Tostmann A, Wertheim H, Bos M, Kolwijck E, Akkermans R, et al. (2017). “Reduced rate of intensive care unit acquired gram-negative bacilli after removal of sinks and introduction of 'water-free' patient care.” Antimicrobial Resistance and Infection Control 6:59. doi:10.1186/s13756-017-0213-0 · PMID 28616203

Building drainage systems

The stack as a transport pathway

Widening the view from one drain to the whole installation raises a different question: can contamination travel between floors and rooms? Both papers are experimental and both have clear limits.

08

Pathogen cross-transmission via building sanitary plumbing systems in a full scale pilot test-rig

Gormley M, Aspray TJ, Kelly DA, Rodriguez-Gil C · 2017 · PLOS ONE

The team built a two-storey sanitary plumbing rig with simulated toilet flushes on the lower floor and a sterile chamber above, and flushed Pseudomonas putida through it. Flushing generated enough turbulence to aerosolise the organism, and airflows typical of a real system (20–30 L/s) carried it between floors. Where a U-trap was empty, the aerosolised organism entered the chamber above, and the organism was recovered throughout the system after flushing.

What it does not show

A laboratory rig with a surrogate organism, not a real building and not a real pathogen. It shows that the physical pathway exists when a trap is dry; it does not show that this route causes disease in occupied buildings. The authors declare that one of them is a named inventor on a defective-trap detection patent and that the work was industry-funded.

Citation

Gormley M, Aspray TJ, Kelly DA, Rodriguez-Gil C (2017). “Pathogen cross-transmission via building sanitary plumbing systems in a full scale pilot test-rig.” PLOS ONE 12(2):e0171556. doi:10.1371/journal.pone.0171556 · PMID 28187135

09

Environmental conditions and the prevalence of norovirus in hospital building drainage system wastewater and airflows

Gormley M, Templeton KE, Kelly DA, Hardie A · 2014 · Building Services Engineering Research and Technology

Wastewater sampled from the collection drain of a hospital building during a norovirus outbreak tested strongly positive for norovirus GII by PCR, confirming that the drainage system itself carries the virus while an outbreak is running. Inside the stack the authors measured an average 24.3 °C and 96.6% relative humidity and confirmed that air moves both up and down it.

What it does not show

Norovirus was not detected in the stack airflow. The authors state plainly that their air-sampling method was ineffective and needs further work. The paper establishes wastewater contamination and a plausible airflow direction, not airborne norovirus reaching a ward.

Citation

Gormley M, Templeton KE, Kelly DA, Hardie A (2014). “Environmental conditions and the prevalence of norovirus in hospital building drainage system wastewater and airflows.” Building Services Engineering Research and Technology 35(3):244–253. doi:10.1177/0143624413485080

Trap seals and dry drains

Pressure, evaporation and precedent

The water in a trap is the only barrier between a room and the sewer. This group is about what happens when that barrier weakens or disappears.

10

Pressure transient identification of depleted appliance trap seals: a pressure pulse technique

Kelly DA, Swaffield JA, Jack LB, Campbell DP, Gormley M · 2008 · Building Services Engineering Research and Technology

An engineering paper that treats the water trap seal as the sole barrier between occupied space and the foul drain, and notes that the pressure transients generated by ordinary appliance discharge are what threaten it. It presents a single-pressure-pulse technique for locating depleted trap seals remotely, validated against a numerical model and by laboratory and site testing.

What it does not show

This is a detection-method paper. It does not itself measure evaporation rates or publish a timetable for how quickly a trap dries out, and its reference to the 2003 Amoy Gardens outbreak is a citation of the public-health investigation rather than original epidemiology.

Citation

Kelly DA, Swaffield JA, Jack LB, Campbell DP, Gormley M (2008). “Pressure transient identification of depleted appliance trap seals: a pressure pulse technique.” Building Services Engineering Research and Technology 29(2):165–181. doi:10.1177/0143624408090202

11

The role of air pressure transients on the spread of bacteria from wash-hand basin sink traps in hospital en-suite bathrooms: a laboratory-based pilot study

Gormley M, Kelly DA, Campbell DP, Aspray TJ, Dight T · 2025 · Journal of Hospital Infection

In a 50 m laboratory pipe network modelling a hospital en-suite, positive air pressure surges in the drainage system pushed water from a wash-hand basin trap containing Pseudomonas alloputida upward into the basin and generated aerosols above the strainer. The strainer became contaminated without any visible ingress of water, and viable bacteria were recovered from surrounding surfaces. The authors describe this as the first demonstration of that mechanism.

What it does not show

A pilot study in a laboratory rig with a surrogate organism. There are no patients, no clinical outcomes and no measurement of how often such pressure surges occur in a working hospital. It concerns wash-hand basin traps rather than floor drains.

Citation

Gormley M, Kelly DA, Campbell DP, Aspray TJ, Dight T (2025). “The role of air pressure transients on the spread of bacteria from wash-hand basin sink traps in hospital en-suite bathrooms: a laboratory-based pilot study.” Journal of Hospital Infection 165:32–40. doi:10.1016/j.jhin.2025.07.026 · PMID 40812395

12

Evidence of airborne transmission of the severe acute respiratory syndrome virus

Yu ITS, Li Y, Wong TW, Tam W, Chan AT, Lee JHW, Leung DYC, Ho T · 2004 · New England Journal of Medicine

The authors analysed the first 187 SARS cases in the Amoy Gardens housing estate in Hong Kong by date of onset and by flat. Risk rose sharply for residents of the middle and upper floors of Block E, a pattern consistent with a rising plume of contaminated warm air in the light well, and computational fluid dynamics and multi-zone modelling reproduced the observed distribution of cases in the neighbouring blocks. The paper concludes that airborne spread best explains the outbreak.

What it does not show

This paper attributes the mechanism to the light well and bathroom exhaust fans; it is not the source of the widely repeated claim that dried floor-drain U-traps caused the outbreak. That attribution comes from the WHO environmental investigation and later reviews of it. Cite this paper for airborne spread at Amoy Gardens, not for the trap-seal mechanism.

Citation

Yu ITS, Li Y, Wong TW, Tam W, Chan AT, Lee JHW, Leung DYC, Ho T (2004). “Evidence of airborne transmission of the severe acute respiratory syndrome virus.” New England Journal of Medicine 350(17):1731–1739. doi:10.1056/NEJMoa032867 · PMID 15102999

Method

How this list was assembled

  • For each paper we checked the authors, year, title and journal against the PubMed, Europe PMC or publisher record, and read the abstract before writing our own summary.
  • Papers we could not verify were left out, however well they would have fitted.
  • Where we found a claim commonly attributed to a paper that its abstract does not actually make, we have said so.

This page is about the risk, not the product. Measured data for Green Drain — flow by model, pressure resistance, thermal cycling, membrane durability and the SGS report on retention of an aerosolised MS2 surrogate — is on the product testing page, with every figure traced to a numbered report and a named laboratory.

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Green Drain™

The product data lives elsewhere.

The product figures, each with a report number and a named laboratory.

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