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Control of bacterial contamination of washbasin taps and output water using Ecasol: a one-year study

Published:March 01, 2012DOI:https://doi.org/10.1016/j.jhin.2012.01.011

      Summary

      Background

      Contaminated washbasin taps and output water are an important source of bacteria that may cause nosocomial infection. A five-week pretreatment study of hot and cold water from 15 washbasin taps at Dublin Dental Hospital showed consistently heavy contamination by aerobic heterotrophic bacteria: mean bacterial counts of 482.5 [standard deviation (SD) 293] colony-forming units (cfu)/mL and 5022 (SD 4322) cfu/mL, respectively.

      Aim

      To minimize microbial contamination of washbasin taps and output water in the long term using the electrochemically generated, pH-neutral disinfectant, Ecasol.

      Methods

      Initially, the 15,000-L water tank providing cold and hot water to washbasins, calorifiers and the distribution network were drained and sediment was removed. The system was shock-dosed with Ecasol 100 ppm to eradicate gross contamination and biofilms. Thereafter, tank water was automatically maintained at Ecasol 2.5 ppm prior to distribution. The microbiological quality of water from five sentinel washbasin taps was monitored weekly for 54 weeks using R2A agar.

      Findings

      The mean counts for hot, cold, mains and tank water during the 54-week study period were 1 (SD 4) cfu/mL, 2 (SD 4) cfu/mL, 205 (SD 160) cfu/mL and 0 cfu/mL, respectively. Swab samples of 33/40 taps, each tested on three separate occasions, yielded no growth on R2A agar, while five samples yielded <20 cfu/swab and two samples yielded >200 cfu/swab. No detrimental effects due to Ecasol were observed in the water network.

      Conclusion

      Ecasol consistently minimized bacterial contamination of washbasin taps and output water in a dental hospital setting.

      Keywords

      Introduction

      Hospital water systems have frequently been identified as a source of nosocomial infection, particularly among immunocompromised and high-dependency patients in areas such as intensive care units.
      • Anaissie E.J.
      • Penzak S.R.
      • Dignani M.C.
      The hospital water supply as a source of nosocomial infections: a plea for action.
      • Ryan M.P.
      • Adley C.C.
      Sphingomonas paucimobilis: a persistent Gram-negative nosocomial infectious organism.
      • Wang J.L.
      • Chen M.L.
      • Lin Y.E.
      • Chang S.C.
      • Chen Y.C.
      Association between contaminated faucets and colonization or infection by nonfermenting Gram-negative bacteria in intensive care units in Taiwan.
      Awareness of Legionella spp. among healthcare workers is fairly high; however, there is less awareness of opportunist pathogens commonly found in hospital water systems. Examples include Pseudomonas spp., Stenotrophomonas spp., Serratia spp., Burkholderia spp., Acinetobacter spp. and Sphingomonas spp., many of which harbour antimicrobial resistance elements.
      • Anaissie E.J.
      • Penzak S.R.
      • Dignani M.C.
      The hospital water supply as a source of nosocomial infections: a plea for action.
      • Ryan M.P.
      • Adley C.C.
      Sphingomonas paucimobilis: a persistent Gram-negative nosocomial infectious organism.
      Anaissie et al.
      • Anaissie E.J.
      • Penzak S.R.
      • Dignani M.C.
      The hospital water supply as a source of nosocomial infections: a plea for action.
      estimated that waterborne Pseudomonas aeruginosa nosocomial pneumonia kills over 1400 patients annually in the USA.
      Patient exposure to waterborne micro-organisms in hospital occurs when bathing, showering or washing hands; during contact with contaminated fixtures (e.g. washbasins and taps); via medical equipment rinsed with water; and by staff transfer.
      • Anaissie E.J.
      • Penzak S.R.
      • Dignani M.C.
      The hospital water supply as a source of nosocomial infections: a plea for action.
      • Ryan M.P.
      • Adley C.C.
      Sphingomonas paucimobilis: a persistent Gram-negative nosocomial infectious organism.
      • Wang J.L.
      • Chen M.L.
      • Lin Y.E.
      • Chang S.C.
      • Chen Y.C.
      Association between contaminated faucets and colonization or infection by nonfermenting Gram-negative bacteria in intensive care units in Taiwan.
      Such micro-organisms may originate from biofilms and sediments in supply water, water storage tanks, and water distribution network pipes and associated equipment.
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      Even in well-maintained water storage tanks supplied with potable water, the water quality can deteriorate rapidly due to the formation of biofilms by bacteria in the supply water.
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      Taps are frequently contaminated with biofilm-containing opportunistic pathogens, especially P. aeruginosa, and numerous cases of cross-infection from hospital taps have been reported.
      • Anaissie E.J.
      • Penzak S.R.
      • Dignani M.C.
      The hospital water supply as a source of nosocomial infections: a plea for action.
      • Wang J.L.
      • Chen M.L.
      • Lin Y.E.
      • Chang S.C.
      • Chen Y.C.
      Association between contaminated faucets and colonization or infection by nonfermenting Gram-negative bacteria in intensive care units in Taiwan.
      Dental unit waterlines, which provide water to cool dental instruments and tooth surfaces, are universally prone to microbial biofilm contamination seeded from supply water.
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.
      Recently, the authors reported the development of an automated system to manage the chemical and microbiological quality of supply and output water at better than potable quality for a network of 103 dental chair units over a three-year period.
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.
      The system used sequential filtrations and automated dosing (2.5 ppm) using the pH-neutral electrochemically activated solution, Ecasol. Ecasol is a highly microbiocidal solution of metastable hypochlorous acid that is capable of penetrating and eradicating biofilms in dental waterlines, water supply pipework and water storage tanks, as determined by electron microscopy and microbial culture analysis.
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.
      Recently, it has been shown that vapourized Ecasol is an effective environmental decontaminant with significant advantages over vapourized hydrogen peroxide.
      • Galvin S.
      • Boyle M.
      • Russell R.J.
      • et al.
      Evaluation of vaporized hydrogen peroxide, Citrox and pH neutral Ecasol for decontamination of an enclosed area: a pilot study.
      The present study investigated the use of Ecasol in controlling microbial contamination of water supplied to washbasin taps in a dental hospital setting.

      Methods

      Water network

      Dublin Dental University Hospital is equipped with 79 washbasins, each with lever-operated mixer taps without thermostatic mixer valves providing hot and cold water. The cold water feed comes from a 15,000-L tank supplied with potable-quality mains water. This tank also supplies calorifiers, which supply hot water to the washbasin taps. Automatic temperature recording is fitted on the out and return legs of the hot water system. Hot water leaves the calorifiers at a mean temperature of 60 °C, and is provided to washbasin taps at a mean temperature of 51 °C after running the water for 1 min. Cold water is provided to washbasin taps at a mean temperature of 14 °C. The tank and its distribution network were installed in 1998. Clinics operate Monday to Friday between 8.30 a.m. and 5.30 p.m, apart from the Accident and Emergency Clinic which operates daily. Hot and cold water outlets are routinely flushed for 3 min every Monday morning and every three days during periods when the clinics are not in regular use. The average water usage from the 15,000-L tank is 7000 L/day. Prior to the present study, the tank was drained, cleaned and disinfected annually with hydrogen peroxide. The mains supply water to Dublin Dental Hospital is regularly subject to chemical analysis.
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      This water is soft with a mean equivalent quantity of calcium carbonate of 32.65 [standard deviation (SD) 0.92] ppm.

      Water sampling and microbiological culture

      Water quality was studied in two phases: a five-week pretreatment phase (June–July 2009) and an Ecasol-treatment phase (September 2009–April 2011). During the pretreatment phase, the hospital’s potable-quality mains water, the 15,000-L tank water, and samples of hot and cold water from 15 washbasins were tested weekly for microbial contamination. The selected washbasins were distributed throughout the hospital’s clinics in disparate locations on three separate floors. Water temperature was recorded at sampling. During a preliminary Ecasol-treatment phase (September 2009–February 2010), hot and cold water samples from five sentinel washbasins located in one large clinic were tested monthly, along with samples from the hospital’s mains supply, and tank water was tested bimonthly. The main Ecasol-treatment phase consisted of a 54-week period (March 2010–April 2011) during which five sentinel washbasins located in one large clinic were tested weekly, along with samples from the hospital’s mains supply, and tank water was tested bimonthly.
      Water samples (50 mL) were collected as described previously after allowing the water to run for 1 min.
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.
      Cold water samples were taken first, followed by hot water samples. Residual free available chlorine (FAC) was neutralized using a 1:1 dilution of 0.5% (w/v) sodium thiosulphate.
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.
      It was found that a 1:1 dilution of sodium thiosulphate 0.5% and Ecasol 100 ppm effectively reduced the FAC to undetectable levels. Standard cell suspensions of P. aeruginosa PAO1 [106 colony-forming units (cfu)/mL] were made in a 1:1 dilution of sodium thiosulphate 0.5% and Ecasol 100 ppm, Ecasol 100 ppm, sodium thiosulphate 0.5% and phosphate buffered saline, respectively, and incubated for 10 min at 20 °C. Aliquots plated on R2A agar (Lab M Ltd., Bury, UK) and incubated for 24 h at 30 °C revealed that Ecasol 100 ppm reduced bacterial counts below detectable levels, while there was no bacterial reduction in neutralized Ecasol relative to controls.
      Study samples were cultured for 10 days at 20–22 °C, in duplicate, on R2A agar to determine total aerobic heterotrophic bacterial density, and colonies were counted using a Flash and Go colony counter (IUL Instruments Ltd., Barcelona, Spain).
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.
      During the pretreatment phase, water samples were also plated on to Pseudomonas agar base (PAB, Oxoid, Basingstoke, UK) medium and on to PAB supplemented with cetrimide (10 mg/mL), fusidic acid (10 mg/mL) and cephaloridine (50 mg/mL) to select for the growth of Pseudomonas spp. and related species. Following incubation at 30 °C for 48 h, colonies were counted as described above. For all samples tested, the characteristics of the recovered colony types and their relative abundance were recorded, and selected colonies were stored at −80 °C prior to identification.
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      During the pretreatment phase, 15 washbasin taps in hospital clinics in disparate locations on three separate floors were swabbed internally using sterile cotton wool swabs (Venturi, Transystem, Copan, Italy) and plated on to R2A agar. During the main Ecasol-treatment phase, washbasin (N = 40) taps in hospital clinics on three separate floors were swabbed three times during the study and plated as before.

      Identification of bacterial isolates

      Bacterial identification was determined by comparing small ribosomal subunit rRNA gene sequences with consensus sequences for individual bacterial species in the EMBL/GenBank nucleotide sequence databases.
      • O’Donnell M.J.
      • Shore A.C.
      • Coleman D.C.
      A novel automated waterline cleaning system that facilitates effective and consistent control of microbial biofilm contamination of dental chair unit waterlines: a one-year study.

      Ecasol

      Ecasol was produced by electrochemical activation (ECA) using a Trustwater 110 ECA generator (Trustwater, Clonmel, Ireland).
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.
      The generator was supplied with potable-quality mains water and a NaCl solution 0.2% (w/v), and produced Ecasol consisting of metastable oxidants (predominantly hypochlorous acid) of approximately 200 ppm at pH 7.0 with an oxidation-reduction potential of +900 mV.
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.
      The energized state relaxes and the activated oxidants gradually revert to the initial ingredients (i.e. water and NaCl) over time (48 h).
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.
      Biosafety studies demonstrated that Ecasol 100 ppm, 40 times higher than the levels used to treat water in the present study (i.e. 2.5 ppm), had no cytotoxic effect on reconstituted human epithelium tissue and was readily inactivated by levels of protein (1–2 g/L) found in saliva.
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.

      Ecasol shock-dosing of water network

      In August 2009, the 15,000-L water tank, distribution network and calorifiers were drained, cleaned thoroughly and all sediment was removed. The tank and distribution network were then filled with fresh mains water and shock-dosed with Ecasol 100 ppm generated by a Trustwater AQ 100 ECA generator. This was left in situ for approximately 6 h to penetrate biofilm and neutralize microbial contamination. The tank was then drained and the water network was flushed with mains water until the Ecasol concentration registered <2 ppm.

      Routine Ecasol treatment of water

      From September 2009, water in the 15,000-L tank supplying the washbasins was automatically dosed with freshly generated Ecasol 2.5 ppm, controlled by an FAC probe and a dosing pump.
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      Previous long-term studies (i.e. three years) of a water network supplying dental chair units treated continuously with Ecasol 2.5 ppm showed no adverse effects to the water network components, dental units or dental instruments.
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.

      Measurement of free available chlorine

      FAC was measured using a Hach Pocket Colorimeter II (Hach Company, Loveland, Colorado, USA).
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.
      FAC concentrations in hot and cold water from all washbasins studied were measured weekly during water sampling in the main Ecasol-treatment phase.

      Statistical analysis

      Variance analyses of bacterial counts were conducted using one-way analysis of variance (Prism Version 3.0; GraphPad Software Inc, San Diego, California, USA). P<0.05 was considered to indicate statistical significance. Bacterial counts are presented as mean (SD).

      Results

      Pretreatment study of washbasin tap water

      A five-week period of microbiological testing of 15 washbasins and the water tank supply showed that all were heavily contaminated with bacteria. The mean aerobic heterotrophic counts from cold water [mean temperature 14 (SD 1) °C], hot water [mean temperature 49 (SD 2) °C], water from the 15,000-L supply tank [mean temperature 9 (SD 1) °C] and mains water [mean temperature 8 (SD 1) °C] during this period were 5022 (SD 4322) cfu/mL, 482.5 (SD 293) cfu/mL, 4358 (SD 3768) cfu/mL and 168 (SD 43) cfu/mL, respectively. The bacterial species identified in the tap water and tank water included Acidovorax temperans, Arthrobacter agilis, Comamonas acidovorans, Chryseobacterium indologenes, Kocuria palustris, Microcococcus luteus, Novosphingobium resinovorum, P. aeruginosa, Pseudomonas fluorescens and Sphingomonas paucimobilis. P. aeruginosa and Sphingomonas and Novosphingobium spp. predominated in cold water (i.e. >50% of total cfu), whereas Sphingomonas and Novosphingobium spp. predominated in hot water. Swab samples taken from the taps from the 15 washbasins showed that the majority were heavily contaminated (>5000 cfu/swab) with bacteria, predominantly Novosphingobium, Sphingomonas and Pseudomonas spp., including P. aeruginosa, with no single species predominating.

      Cleaning of water distribution network

      As a consequence of the pretreatment phase, the water tank was cleaned and both the hot and cold water networks providing water to the washbasins were shock-dosed with Ecasol 100 ppm. Following this, a residual Ecasol concentration of 2.5 ppm was maintained in the system from September 2009 onwards (Ecasol-treatment phase). Between September 2009 and February 2010, monthly tests of tank water, and hot and cold water samples from five of the sentinel washbasin outlets used in the pretreatment phase revealed greatly reduced levels of aerobic heterotrophic bacteria in tank water (mean <1 cfu/mL), cold water (mean <1 cfu/mL) and hot water (mean <4 cfu/mL). Based on these preliminary findings of the Ecasol-treatment phase, the efficacy of Ecasol for minimizing microbial contamination was monitored weekly for a further 54 weeks between March 2010 and April 2011.

      Long-term study of Ecasol efficacy

      From March 2010, hot and cold water from five washbasins was tested weekly over 54 consecutive weeks for density of aerobic heterotrophic bacteria and residual FAC concentrations. Most (257/270, 95.2%) cold water samples [mean temperature 14 (SD 1) °C] yielded no growth on R2A agar. Of the 13 remaining samples, 12 samples yielded ≤20 cfu/mL and one sample yielded 100 cfu/mL. The mean bacterial count from the cold water outlets of the five washbasins was 1 (SD 4) cfu/mL. Most (235/270, 87%) hot water samples [mean temperature 50 (SD 2) °C] also yielded no growth on R2A agar. Of the 35 remaining samples, 34 samples yielded ≤20 cfu/mL and one sample yielded 100 cfu/mL. The mean bacterial count from the hot water outlets of the five washbasins was 2 (SD 4) cfu/mL. Ecasol-treated tank water [mean temperature 10 (SD 1) °C] was tested at bimonthly intervals; on each occasion, no organisms were recovered. Overall, the reduction in aerobic heterotrophic bacterial density between pre- and post-treatment was highly significant for both cold (P<0.0001) and hot (P = 0.002) water. The mean bacterial density in the mains water [mean temperature 8 (SD 1) °C], tested weekly during the study period, was 205 (SD 160) cfu/mL. Figure 1 shows an example of the bacterial density in hot and cold water from a representative washbasin during the study period, together with the corresponding density in the mains water. The mean FAC concentrations in cold and hot water during the period was 1.3 (SD 0.6) ppm and 0.17 (SD 0.2) ppm, respectively. The pH of Ecasol-treated tap water (cold and hot) and mains water tested at intervals was 7.46 (SD 0.02), 7.29 (SD 0.02) and 7.35 (SD 0.01), respectively. Following completion of the 54-week study, the Ecasol dosing system and the calorifiers were taken offline for a week due to building works. By the end of the week, the bacterial density in tap water had increased to >300 cfu/mL, but returned to treatment-phase levels within a few days of recommencing Ecasol treatment.
      Figure thumbnail gr1
      Figure 1The aerobic heterotrophic bacterial density on R2A agar recovered from a representative washbasin supplied with Ecasol-treated water in comparison with mains water over a 54-week period. Green triangles indicate cold water, red circles indicate hot water and black squares indicate mains water.
      All water networks in Dublin Dental Hospital are subject to six-monthly Legionella spp. surveillance by culture on buffered charcoal yeast extract agar. These include hot and cold water from washbasins, tank water and mains water. To date, no Legionella spp. have been detected on culture, including during the study period.
      Swab samples taken from 33/40 washbasin taps tested on three occasions during the 54-week study yielded no bacterial growth. Swab samples from the remaining seven taps were culture-positive; however, only two of these samples yielded >200 cfu/swab. The other five taps yielded <20 cfu/swab on each occasion sampled. These taps were replaced and no bacterial growth was recovered following swab sampling over several weeks. Swabbing of the old taps after removal revealed contamination within the hot water inlet of two of the taps, which yielded confluent growth of Sphingomonas spp. when cultured on R2A agar. The cold water inlets yielded no growth.

      Lack of adverse effects on the water network

      During the study period, routine checks on the water distribution network supplying the washbasins showed no adverse effects. No leaks or corrosion were observed on pipework, taps, pumps or other components.

      Discussion

      In 2010, the UK Director of Health Protection highlighted the potential of taps and sinks as infection reservoirs (http://tiny.cc/xjfww). Many strategies have been investigated to control this type of bacterial contamination, including the use of chemical disinfectants such as chlorine, monochloramine, chlorine dioxide, ozone, copper/silver ion seeding, ultraviolet irradiation and the use of tap terminal filters.
      • Fujitani S.
      • Sun H.Y.
      • Yu V.L.
      • Weingarten J.A.
      Pneumonia due to Pseudomonas aeruginosa. Part I. Epidemiology, cinical diagnosis, and source.
      • Ortolano G.A.
      • McAlister M.B.
      • Angelbeck J.A.
      • et al.
      Hospital water point-of-use filtration: a complementary strategy to reduce the risk of nosocomial infection.
      • Chord F.
      • Fascia P.
      • Mallaval F.
      • et al.
      Chlorine dioxide for Legionella spp. disinfection: a danger for cross-linked polyethylene pipes?.
      Chlorine dioxide can be very effective at controlling microbial contamination in water networks in hospitals; however, disadvantages include storage and handling of hazardous chemicals, and adverse effects on plastic and metal water pipes resulting in leaks.
      • Chord F.
      • Fascia P.
      • Mallaval F.
      • et al.
      Chlorine dioxide for Legionella spp. disinfection: a danger for cross-linked polyethylene pipes?.
      Ultraviolet treatment of water can be adversely affected by suspended material and flow rates, and it has no residual activity to counter reverse flow biofilm colonization. Use of elevated temperature, and copper and silver ions can decrease the colonization of P. aeruginosa in hospitalized patients, but is unable to eradicate biofilm within taps.
      • Fujitani S.
      • Sun H.Y.
      • Yu V.L.
      • Weingarten J.A.
      Pneumonia due to Pseudomonas aeruginosa. Part I. Epidemiology, cinical diagnosis, and source.
      Point-of-use filters fitted to tap outlets have been effective in eliminating a range of micro-organisms from output water and decreasing the patient infection rate.
      • Ortolano G.A.
      • McAlister M.B.
      • Angelbeck J.A.
      • et al.
      Hospital water point-of-use filtration: a complementary strategy to reduce the risk of nosocomial infection.
      • Marchesi I.
      • Marchegiano P.
      • Bargellini A.
      • et al.
      Effectiveness of different methods to control Legionella in the water supply: ten-year experience in an Italian university hospital.
      However, such filters are expensive and have to be changed regularly.
      • Cooke R.P.D.
      • Whymant-Morris A.
      • Umasankar R.S.
      • Goddard S.V.
      Bacteria-free water for automatic washer-disinfectors: an impossible dream?.
      Two previous long-term studies found that treatment of dental chair unit supply water using Ecasol 2.5 ppm provided an effective and safe solution to the problem of dental waterline biofilm.
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.
      The present study has shown reductions in mean aerobic heterotrophic bacteria from >5000 cfu/mL to 1 cfu/mL for cold water supplied to washbasins, and from 500 cfu/mL to 2 cfu/mL for hot water supplied to washbasins. This significant reduction was achieved and sustained over the 54-week study period following initial cleaning and shock-dosing with Ecasol 100 ppm, followed by continuous treatment with Ecasol 2.5 ppm (Figure 1). Similar to previous studies of long-term dental waterline disinfection with Ecasol, no evidence for the emergence of bacteria that were tolerant or resistant to Ecasol was observed during the study. No adverse effects on the water distribution network or taps due to Ecasol were observed, and none were reported previously in water networks supplying dental units with Ecasol-treated (2.5 ppm) water.
      • O’Donnell M.J.
      • Boyle M.
      • Swan J.
      • Russell R.J.
      • Coleman D.C.
      A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: a 2-year longitudinal study.
      • Boyle M.A.
      • O’Donnell M.J.
      • Russell R.J.
      • Coleman D.C.
      Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models.
      At 2.5 ppm, Ecasol contains low residual chloride (3–4 ppm and 30–40 ppm from Trustwater AQ and ECA 110 Ecasol generators, respectively), minimizing the potential for salt corrosion. Persistent bacterial biofilm was observed in the hot water inlets of five problematic taps, but this contamination issue was resolved by replacing the taps. These findings indicate that specific water network components can act as reservoirs of ongoing contamination, probably due to accumulation of scale, sediment and/or biofilms shielding contaminating micro-organisms from disinfection. Sphingomonas spp. and related species produce abundant viscous exopolysaccharides that enable the organisms to readily form dense biofilms, which can protect more harmful bacteria such as P. aeruginosa.
      • Wang J.L.
      • Chen M.L.
      • Lin Y.E.
      • Chang S.C.
      • Chen Y.C.
      Association between contaminated faucets and colonization or infection by nonfermenting Gram-negative bacteria in intensive care units in Taiwan.
      • Fujitani S.
      • Sun H.Y.
      • Yu V.L.
      • Weingarten J.A.
      Pneumonia due to Pseudomonas aeruginosa. Part I. Epidemiology, cinical diagnosis, and source.
      These species were recovered in significant numbers from both hot and cold tap water, but predominated in hot water. Previous studies have shown that Sphingomonas spp. can tolerate temperatures up to 55 °C in water.
      • Mitsuru E.
      • Ostrowski W.
      • Fegatella F.
      • et al.
      Sphingomonas alaskensis strain AFO1, an abundant oligotrophic ultramicrobacterium from the north pacific.
      The lower FAC concentrations recorded in hot tap water relative to cold tap water is a normal effect of heating Ecasol, similar to that seen with conventionally chlorinated water. This, however, did not have an adverse effect on the ability of residual Ecasol to minimize bacterial counts in hot tap water. Water hardness is not an issue at Dublin Dental Hospital. In areas with hard water, it would be prudent to soften the water before using Ecasol. This makes the process of disinfection easier by reducing deposits and sediment that can encourage biofilm growth.
      In the study hospital, automated Ecasol treatment of water provided a cost-effective long-term solution for the problem of microbial contamination of taps and output water. Installation costs for Ecasol-generating equipment, pumps and probes were approximately €35,000, annual running costs are <€1000 and annual maintenance costs are approximately €3000. For a large acute hospital, an Ecasol AQ generator would be required, which is capable of treating millions of litres of water per day. Installation and running costs would be approximately double the figures shown above. In contrast, the estimated cost of point-of-use water filters for washbasin taps in the study hospital would be approximately €12,000/year.

      Conflict of interest statement

      None declared.

      Funding sources

      This study was supported by the Dublin Dental University Hospital Microbiology Unit and by Health Research Board Grant HRA_PHS/2011/2 .

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