Negligible influence of limescale deposits on faucet aerators on measured microorganism loads

Abstract

Introduction

The study was conducted to assess the effects of limescale deposits on faucet aerators on the qualitative and quantitative detection of microorganisms from swabbing and first jet water samples.

Methods

Limescale deposits on faucet aerators were categorized into three groups: not / slightly calcified, moderately calcified and heavily calcified. Colonization was assessed by isolating microorganisms from standardized swabbing and water samples. Microorganisms isolated from the aerators were compared with clinical isolates from the same year.

Results

Regardless of the degree of calcification on the faucet aerators, similar numbers and types of microorganisms were found. Except for Staphylococcus epidermidis and the rare occurrence of Staphylococcus aureus and Nacaseomyces glabratus on the aerators, there were no matches between the microorganisms isolated from the aerators and the top ten clinical isolates. Microorganisms frequently isolated from aerators, such as Sphingomonas paucimobilis, were extremely rare in clinical samples. No differences in species were observed based on the degree of calcification of the aerators.

Conclusions

The study did not demonstrate a significant effect of the degree of calcification on the colonization of aerators. Although calcification of aerators as a risk factor for increased microbial transmission cannot be entirely dismissed, its importance appears to be secondary.

1. Introduction

Contaminated tap water is a significant source of infectious agent transmission [1–14], both in community settings [13, 14] and hospitals [1, 2, 4, 5, 7, 8–12]. Accordingly, drinking water is subjected to strict quality control measures to assess microorganism loads, as outlined in guidance documents such as DIN EN ISO 19458, which is the reference document for Germany where the study was conducted.

In addition to these validated and reliable quality assessment standards, less standardized and more indirect quality indicators have emerged in routine hygiene counselling in inpatient settings. One such indirect criterion is the degree of calcification of faucet aerators, which can vary due to factors like water hardness, flow rate, and simply the duration of use. The underlying hypothesis for using this indicator is the assumption that limescale deposits complicate cleaning procedures, potentially leading to higher microorganism loads and increased infection risks. Besides direct water contact or consumption, indirect contacts within a radius of up to 2 m due to splash water or even farther due to aerosols may also be relevant for transmission events [1–12]. Hospital infections or nosocomial colonization associated with contaminated faucet aerators have been particularly reported for less virulent bacteria like Acinetobacter junii [15] and Stenotrophomonas maltophilia [16, 17], highlighting the need for regular cleaning of aerators in healthcare settings.

Despite these theoretical assumptions on a potential relevance of limescale deposits on aerators, evidence remains widely lacking in international literature. Nevertheless, hygiene authorities' demands for the regular replacement of calcified aerators often incur significant costs.

To address whether limescale deposits on aerators facilitate the transmission of microorganisms, this study aimed at evaluating the microbial load on three categories of differently calcified aerators using swabbing samples and first jet water samples. A qualitative assessment of the recorded microorganisms was performed to document identified genera and species, while a quantitative assessment estimated the microbial load comparing aerators of different calcification categories in a German tertiary hospital. The obtained results were compared to surveillance data on microbial isolates from infectious disease patients within the same hospital during the study to identify likely transmission events.

2. Methods

2.1. Setting and study sites

Faucet aerators at the University Medicine Rostock, Germany, are installed on each faucet. Depending on the location in patient or staff rooms, they are included in a daily or twice weekly cleaning program. Therefore, the aerators are wiped with a limescale removing agent. The aerators are not exchanged on a regular schedule, but when the local staff reports them as being heavily calcified.

The water quality at the University Medicine Rostock is controlled on a regular basis according to the specific German law (“Trinkwasser-Verordnung” = drinking water regulation), which includes water sampling through the installed aerators, but only after passing at least 3 liter of water through them. The water quality concerning bacterial counts and presence of potential fecal contaminants during the study period was well within the limits of the regulation. Only Legionella sp. counts were occasionally above the limits of the regulation, although not at the faucets examined in this study. During the study period, no increased numbers of infections or outbreaks by water-borne agents were recorded. Also no legionellosis case was identified in spite of regular testing of respiratory samples by molecular techniques.

For the present study, sampling of faucet aerators was performed across normal care units at seven different medical departments at University Medicine Rostock: surgery (outpatient department, cardiac surgery), orthopedics, ear-nose-and-throat medicine, internal medicine (endocrinology, pulmonology, cardiology, and nephrology), neurology, ophthalmology and pediatrics. All faucets were located in the patients' wet rooms.

2.2. Sampling technique

Observed limescale deposits on faucet aerators were categorized as follows: I) not / slightly calcified (no calcification or only small deposits), II) moderately calcified (defined by an interrupted ring of limescale) and III) heavily calcified (aerator covered by a continuous ring of limescale). The degree of calcification was photographically documented using a Sony Digital Still Camera DSC-RX100 (Sony Corporation, Tokyo, Japan) from the front as well as from left and right angles. Figure 1a–c shows aerators representative of each calcification category. The sampling was performed to ensure that all three calcification categories were approximately equally represented, comprising 90 aerators: 30 classified as non / slightly calcified, 28 as moderately calcified, and 32 as heavily calcified. The distribution of the calcification categories across the various medical departments is summarized in the Supplementary Material 1.

Fig. 1.

a–d. Categories of lime deposits on faucet aerators and swab-based sampling technique. a) not / slightly calcified (no calcification or only small deposits), b) moderately calcified (defined by a yet interrupted ring of limescale) and c) heavily calcified (aerator covered by a continuous ring of limescale). d) Aerators were sampled comprising one swipe along the outside metal ring, followed by two more swipes across the underside surface in a perpendicular manner

Each aerator was sampled by swabbing (Σ-Swab; Medical Wire & Equipment Co., Ltd., Corsham, UK). This process comprised one swipe along the outside metal ring, followed by two more swipes across the underside surface in a perpendicular manner as shown in Fig. 1d. Swabs were then placed in a 15 mL plastic tube (Greiner Bio-One GmbH, Frickenhausen, Germany) containing 1 mL NaCl solution (0.9%). Subsequently, 5 mL of cold first jet water was collected in a separate 15 mL plastic tube (Greiner Bio-One GmbH). Time elapsed from sampling to processing in the laboratory was a maximum of 45 min.

2.3. Culture-based diagnostic approaches

Ten-fold serial dilutions were prepared from both swab and water samples. 100 µL of undiluted suspension from the swab tubes, 250 µL of the water sample, and 100 µL from each dilution series were homogenously applied onto Columbia agar with 5% sheep blood (Becton Dickinson, Heidelberg, Germany) and chocolate agar (Becton Dickinson) with glass beads (Carl-Roth GmbH + Co. KG, Karlsruhe, Germany). The agar plates were then incubated at 37 °C in an atmosphere with 20% oxygen and 5% carbon dioxide for five days. As only microorganisms capable of aerobic growth were expected in the aerator samples, no culturing under anaerobic conditions was performed.

The culture media were assessed for microorganisms on days two and five of the incubation period. The number of morphologically identical colonies was quantified. One colony of each morphology was isolated on Columbia agar (Becton Dickinson) unless growth was only observed on chocolate agar (Becton Dickinson), in which case chocolate agar (Becton Dickinson) was used for isolation. The passaged colonies were incubated for an additional two days under the aforementioned atmospheric conditions.

2.4. Differentiation of isolates

Colony material was identified using matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (Vitek MS IVD V2, database MS-CE version CLI 2.0.0; bioMérieux Deutschland GmbH, Nürtingen, Germany) according to the manufacturer's instructions. If this method failed, identification was biochemically attempted using GP and GN ID cards of the Vitek 2XL system (bioMérieux), depending on their Gram staining results. For suspected Enterobacterales and non-fermentative rod-shaped bacteria, the analytical profile index (API) 20E/NE fast identification system (bioMérieux) was used. Finally, the RapID CB Plus panel (Remel, Lenexa, USA) was employed, each in line with the manufacturers' recommendations, in descending order of application.

If the colony identity could not be resolved by mass spectrometry or any of the aforementioned morphological and biochemical assessments, DNA of a pure colony was extracted using the QIAamp DNA Mini Kit (Qiagen N.V., Hilden, Germany) and subsequently subjected to either 16S rRNA gene-based pan-bacterial PCR [18] or 18S rRNA gene-based pan-fungal PCR [19]. The oligonucleotides used are shown in Supplementary Material 2. The obtained bacterial and fungal amplicons were purified by agarose gel electrophoresis using 1.2% agarose gels and sent for commercial Sanger sequencing to Seqlab (Microsynth AG, Göttingen, Germany). The returned sequence files were quality-controlled using Finch Trace Viewer software (Geospiza Inc., Seattle, WA, USA) and analyzed with the Basic Local Alignment Search Tool (BLAST) provided by the National Center for Biotechnology Information (NCBI). Matches of ≥99% were accepted as identifications at the species level, and matches of ≥97% but <99% were accepted as identifications at the genus level.

2.5. Interpretation of the results and statistics

Detected microorganisms were assigned to 11 groups: Bacillaceae, Caulobacteraceae, Comamonadaceae, Enterobacterales, Micrococcaceae, non-fermenting bacteria, molds, Sphingomonadaceae, yeasts, Staphylococcaceae, and Streptococcaceae. Bacteria and fungi that could not be attributed to one of these 11 groups were classified as “other microorganisms”.

Microorganism loads of each of the aforementioned groups were individually assessed for the different limescale deposit categories of the aerators. Mean loads of ≥10 – <100 CFU (colony-forming units) per swab / mL were considered low, ≥100 – <1000 CFU per swab / mL intermediate, and ≥1000 CFU per swab / mL high levels of bacterial or fungal growth for both swabs and water samples.

Surveillance data of clinical isolates within the study year at the university hospital were obtained for comparison purposes from the laboratory information system (LIS) of the microbiological routine diagnostic laboratory.

Statistical analysis was performed using GraphPad Prism version 5.0 (GraphPad Software Inc., San Diego, CA, USA). In addition to calculating descriptive parameters such as arithmetic means and standard deviations, Kruskal–Wallis testing was applied to compare microorganism loads in swab and water samples collected from faucet aerators.

2.6. Ethics

Ethical clearance for the assessment was unnecessary in accordance with national German laws, as neither patient data nor patient sample materials were included in the assessment.

3. Results

3.1. Quantitative assessment of total swab-based isolates according to the degree of calcification on the faucet aerators

Focusing on the absolute numbers of detected microorganisms, the group of not / slightly calcified aerators was found to carry the lowest microbial loads, with a mean ± standard deviation (SD) of 4,838 ± 10,817 CFU (colony forming units) per swab. Moderately calcified aerators were associated with the highest microbial loads, with a mean ± SD of 14,804 ± 23,013 CFU per swab. The mean ± SD microbial load of heavily calcified aerators was 11,113 ± 22,243 per swab. Kruskal–Wallis testing suggested a non-significant difference with a P-value of 0.057. Minor differences observed across the various assessed medical departments are visualized in the Supplementary Material 3.

3.2. Classification of swab-based isolates in pathogen groups

Not / slightly calcified aerators showed a high level of colonization with bacteria from the groups Caulobacteraceae, Sphingomonadaceae and “other microorganisms”, while intermediate levels were found only for non-fermenting bacteria. Low levels were associated with other groups of microorganisms, while yeasts were not detected at all (Fig. 2). Focusing on relative colonization rates, Sphingomonadaceae was the most frequently identified group of bacteria isolated from swab samples, with a proportion of 67% (20/30) within the stratum of not / slightly calcified aerators. Caulobacteraceae, Staphylococcaceae, and “other microorganisms” were detected in at least 10 samples. The least frequently observed groups were Bacillaceae, Enterobacterales and molds with only 2 colonized aerators each (Supplementary Material 4).

Fig. 2.

Microbial loads on faucet aerators. The mean values and standard deviations of the microbial loads on aerators across all three degrees of calcification, determined by swabbing, are visualized for the individual microorganism groups in a logarithmic scale. Very small values for bacterial counts or standard deviations are not graphically represented due to the chosen logarithmic scale. CFU = colony forming unit

Moderately calcified aerators were colonized with high levels of bacteria from the groups Caulobacteraceae, Comamonadaceae, Sphingomonadaceae and “other bacteria”. Intermediate levels were seen for the groups Micrococcaceae and molds, while other groups showed only low levels of microorganisms (Fig. 2). Within the moderately calcified stratum of aerators, Sphingomonadaceae were most frequently isolated from the swabs, with a proportion of 86% (24/28). Caulobacteraceae, Comamonadaceae, Staphylococcaceae and “other microorganisms” were detected in at least 10 samples each. The least frequently recorded groups were Enterobacterales, yeasts and Streptococcaceae (<4%) (Supplementary Material 4).

Heavily calcified aerators showed high levels of microorganisms from the groups of non-fermentative bacteria, Sphingomonadaceae, and “other microorganisms”. Intermediate levels were found for Caulobacteraceae, Comamonadacae, Micrococcaceae, molds, and Streptococcaceae, while low levels were observed for Bacillaceae, yeasts, and Staphylococcaceae. No bacteria from the Enterobacterales group were isolated (Fig. 2). Within the heavily calcified class of aerators, Sphingomonadaceae were the most frequently recorded ones, with a proportion of 69% (22/32). The group of “other microorganisms” was detected in 10 samples (≥31%). Representatives of all other groups were isolated as colonizers on fewer than 10 aerators, with yeasts and Bacillaceae in only one sample (<4%) each (Supplementary Material 4).

3.3. Quantitative assessment of total water sample derived isolates according to the degree of calcification of the faucet aerators

Not / slightly calcified aerators carried the lowest number of bacteria, with a mean ± SD of 11,458 ± 15,069 CFU/mL. Moderately calcified aerators had a mean bacterial load of 24,868 ± 32,868 CFU/mL, while heavily calcified aerators had the highest calculated microbial load of 27,170 ± 51,883 CFU/mL. The Kruskal–Wallis test yielded a P value of 0.133, indicating a non-significant result. Minor differences across the various assessed medical departments are shown in the Supplementary Material 5.

3.4. Classification of the water sample derived isolates in pathogen groups

Not / slightly calcified aerators were associated with high levels of microorganisms from the groups Caulobacteraceae, non-fermenting bacteria, Sphingomonadaceae, and “other microorganisms”. Intermediate levels were recorded for Comamonadaceae, Enterobacterales, and Streptococcaceae, while low levels were observed for all remaining groups (Fig. 3). Focusing on relative frequencies of detection, Sphingomonadaceae were the most frequently occurring bacteria isolated from water samples, with a proportion of 77% (23/30) within the stratum of not / slightly calcified aerators, while “other microorganisms” were found in 70% (21/30) of the samples. Caulobacteraceae and non-fermenting bacteria were detected in at least 10 samples (≥33%). Molds were the least frequently recorded microorganisms, with a proportion 7% (2/30) (Supplementary Material 6).

Fig. 3.

Microbial loads on faucet aerators. The mean values and standard deviations of the microbial loads on aerators across all three degrees of calcification, determined by water sampling, are visualized for the individual microorganism groups in a logarithmic scale. Very small values for bacterial counts or standard deviations are not graphically represented due to the chosen logarithmic scale. CFU = colony forming unit

Moderately calcified aerators were associated with high levels of Caulobacteraceae, Comamonadaceae, Sphingomonadaceae, and “other microorganisms”. Intermediate levels of Enterobacterales and Staphylococcaceaea were observed, while low levels were recorded for all remaining groups (Fig. 3). Within the moderately calcified class of aerators, Sphingomonadaceae were most frequently isolated, with a proportion of 93% (26/28). Caulobacteraceae, Comamonadaceae, and “other microorganisms” were detected in at least 10 samples (≥36%). The least frequently recorded groups were Enterobacterales, yeasts, and Streptococcaceae with only 2 colonized samples each (Supplementary Material 6).

Heavily calcified aerators showed colonization at high levels with Caulobacteraceae, non-fermenting bacteria, Sphingomonadaceae, and “other microorganisms”. Intermediate levels were observed with Streptococcaceae, Comamonadacae, and Micrococcaceae, while low levels were found in all remaining groups. Yeasts were not detected in any of the water samples (Fig. 3). Within the heavily calcified class of aerators, Sphingomonadaceae were most frequently observed, with a proportion of 84% (27/32) followed by Caulobacteraceae, which were detected in 21 samples (66%). Non-fermenting bacteria and “other microorganisms” were observed in at least 10 samples (≥31%) each, while Enterobacterales and Streptococcaceae were isolated from only 3 samples (9%) each (Supplementary Material 6).

3.5. Matching of the isolates to microbiological surveillance data on patient isolates

From the ten most frequently isolated microorganisms from clinical samples with presumed etiological relevance within the study year, only three were also isolated from the aerator samples. Staphylococcus aureus and Nakaseomyces glabratus (formerly Candida glabrata) were each isolated once, while Staphylococcus epidermidis was detected in 17 (19%) swabs and 11 (12%) water samples distributed across all degrees of aerator calcification (Table 1).

Table 1.

The ten most common microorganisms detected in patient samples during clinical surveillance in the study year at the assessed university hospital, depicted in descending frequency and in relation to the frequency of detection of the corresponding microbial detections on swabs and in water samples from aerators in this study. The stratification is based on the degree of calcification of the aerators

Pathogen	Number (n) of patient isolates in the year of assessment	Number (n) of isolations by swabbing stratified by degree of calcification			Number (n) of isolations from water samples stratified by degree of calcification
		Not / slightly calcified	Moderately calcified	Heavily calcified	Not / slightly calcified	Moderately calcified	Heavily calcified
Escherichia coli	2,112
Staphylococcus aureus	1,999		1
Enterococcus spp.	1,517
Candida albicans	1,089
Staphylococcus epidermidis	1,060	8	4	5	4	1	6
Klebsiella pneumoniae sive oxytoca	746
Pseudomonas aeruginosa	610
Proteus spp.	518
Enterobacter cloacae sive aerogenes	343
Nakaseomyces glabratus (formerly Candida glabrata)	282			1

n = number, spp. = species.

A summary of the most frequently identified microorganisms from swabbing and water samples of the swab assessment, defined as n ≥ 10 isolation events, is shown in Supplementary Materials 7 and 8, respectively. These tables also include the corresponding number of isolations of each microorganism from clinical samples within the year of the study. The most frequently identified microorganisms from the aerators were Sphingomonas spp. in general, and Sphingomonas paucimobilis in particular, with successful isolation from 60 swabs and 65 water samples. S. paucimobilis was the only representative of the genus Sphingomonas that was also infrequently isolated in a clinical context. However, the total number of seven isolation events from clinical samples remained low in the year of the study. S. epidermidis was the only species frequently isolated both from aerator samples and clinical samples. Representatives of Bacillus spp. were recorded in 20 water samples, five swab samples, and in six clinical samples. Brevundimonas spp. were isolated 34 times from swabs and 50 times from water samples but were never found in patient samples.

4. Discussion

The study was conducted to assess the effect of calcification in faucet aerators on the risk of waterborne nosocomial pathogen transmission. The assessment led to several findings.

First, and not surprisingly, microorganisms previously associated with waterborne hospital infections [6–11], particularly in immunocompromised individuals, such as S. paucimobilis and Pseudomonas spp., were occasionally detected in the analyzed samples. Shingomonadaceae and the also recorded Caulobacteracea are known for biofilm formation and partly also for facilitating limescale precipitation in water pipes [20–22], making their detection expectable.

Second, there was no indication of an association between the degree of limescale deposits and a) the microbial load at the analyzed aerators, b) the microbial spectrum, and c) the abundance of pathogenic microorganisms as compared to etiologically relevant pathogen detections in patient samples collected at the hospital during the study year. Trends for more microorganisms on more heavily calcified faucet aerators were not found to be significant.

Third, focusing on the latter, only the species Nakaseomyces glabratus (formerly C. glabrata), S. aureus and S. epidermidis, which are human commensals, were isolated from aerators during the study, with S. epidermidis being the most frequent. There was no clear association with the degree of calcification. Apart from these exceptions, there was no obvious correlation between aerator-associated organisms and the spectrum of microorganisms with assumed etiological relevance isolated from inpatients. Instead, the spectrum of isolates obtained in the study comprised commensal skin colonizers and typical aquatic microorganisms rather than typical pathogens. Nevertheless, severely immunocompromised patients can even be endangered by microorganisms with very low virulence such as the frequently observed aquatic bacterium S. paucimobilis [23].

Fourth, low to moderate differences in microbial colonization of the aerators at the various study sites were observed. These differences were most likely due to local sources of contamination, particularly due to inhabitants of the buildings, as suggested by other authors [24].

Focusing on the main study question, the data collected show that an increasing degree of calcification of the aerators does not correlate with an increased risk for patients in terms of microbial load or the isolated pathogen spectrum. However, the qualitative and quantitative comparison does not fully answer whether limescale deposits might negatively interfere with cleaning or disinfection attempts at the aerators. Limescale deposits are suspected of forming micro-cavities that protect bacteria from being washed out and from disinfectants, leading to rapid reemergence after a disinfection procedure [25]. The increased surface area due to micro-cavities, combined with positively charged calcium ions, could hypothetically further support the resilience of colonizing bacteria to cleaning and disinfection procedures by facilitating biofilm formation, as suggested by others [26]. As the assessment of cleaning and disinfection procedures was beyond the scope of this study, this question remains unresolved and subject to future research.

Focusing on the technical aspects of the assessment, it must be admitted that the three chosen calcification categories were arbitrarily defined as a reproducible stratification strategy. Accordingly, other stratification criteria could have been applied as well. Additionally, the combined assessment of swabs and water samples deserves further explanation. The inclusion of the swabbing scheme was due to the fact that aerator-associated contamination includes the outside surface of the aerator. Furthermore, bacterial pathogens might be organized in biofilms rather than occurring in planktonic stages [26]. The applied polyurethane swab was chosen because of its documented good performance regarding the recovery of microorganisms combined with well-defined rigidity [27, 28]. This choice reduced the likelihood of swab damage due to fraying on the rough lime surface, which has been observed with other types of swabs [29]. Due to this approach, optimized recovery rates of microbial pathogens can be assumed. In addition to the swabbing approach, a water assessment was performed. In contrast to established standard methods for drinking water assessments described in guidance documents like DIN EN ISO 19458, which is considered as the German reference standard for such analyses, first jet water was taken for the assessments. This deviation was necessary because the influence of the flow at the aerator needed to be evaluated, rather than the general drinking water quality, which is monitored annually in the German hospital setting. As swab assessment and water assessment provided comparable results with slightly more microbial detections in water samples, the use of easier-to-take water samples may be considered as a standard for future comparable studies. Such a decision would also reduce potential bias due to varying quality of swabbing by different investigators.

The study has several limitations. First, the exploratory nature of the assessment made a priori case number assessment unfeasible. Therefore, the chosen case numbers were investigator-defined rather than calculated. Consequently, it must be assumed that small differences below the significance threshold for the chosen sample numbers within each group may have been overlooked. Second, as stated above, the study design describes the standard situation, not the situation directly after cleaning or disinfection procedures at the aerators. Therefore, it cannot be excluded that severe calcification might negatively interfere with short-term effects of cleaning and disinfection procedures. Future studies should address this issue. Third, only microorganisms growing under the chosen aerobic standard conditions were assessed. It is possible that less easy-to-grow microorganisms were missed either due to lack of growth or overgrowth by fast-growing ones. This includes microorganisms of etiological relevance like Legionella pneumophila. A quantitative molecular diagnostic approach, including modern techniques like quantitative real-time PCR, digital-droplet PCR or next-generation sequencing, would have provided deeper insights but was unfeasible due to funding constraints. Also, direct cell counting in the water samples with flow cytometry approaches might be considered in future assessments. Fourth, methodologic issues comprise limitations of biochemical or mass spectrometry-based pathogen identification apart from microorganisms commonly isolated from patient samples, making some of the differentiation results potentially uncertain. For this reason, 16S- and 18S-rRNA gene sequencing was added in case of instances of uncertain or contradicting differentiation results. However, the use of sequence information from a non-curated database as conducted for the assessment provided here again bears the risk of potential misidentifications as repeatedly suggested elsewhere [30–33]. Fifth, it is difficult to define infection-relevant doses for most identified microorganisms, although it can generally be assumed that a high microbial load at the aerator might lead to an increased inoculation dose and thus more likely result in an infection. The individual inoculation dose required for an infection depends not only on the microorganism but also on the immune status of the affected person, the transmission route, and the abundance of virulence factors, as known for decades [34]. This explains the absence of well-established cut-offs. Nevertheless, the poor correlation between pathogens identified by microbiological patient surveillance and the assessment of the aerators suggests little etiological relevance of the detected microbial colonization in the setting of the investigated university hospital. Sixth, the assessment was designed as a holistic, exploratory, hypothesis-forming study only. Future studies should include more epidemiological and infection prevention and control-associated meta-data. In particular, stratification should be based on medical care level specifically addressing basic, intermediate and intensive care as well as on direct patient use of the faucets in the patients' wet rooms. Such a strategy will facilitate the assignment of outbreak events with waterborne pathogens, which was only holistically conducted for the study presented here. Further, all assessed aerators should be subjected to standardized procedures regarding their exposure to limescale-removing agents, disinfection approaches and definitions of requirement for their replacement in order to ensure better comparability.

5. Conclusions

In spite of the aforementioned limitations, the study results suggest that although aerator calcification as a risk factor of increased microbial transmission probability cannot be completely ruled out, its relevance is certainly secondary. An association with the degree of calcification appears unlikely. Accordingly, the expensive current practice of exchanging aerators in the medical healthcare setting solely due to the observation of lime deposits is not justified based upon the study results.

Supplementary material

eujmi-15-103-s001.pdf ^{(258.7KB, pdf)}

Data availability

All relevant data are provided in the manuscript and its supplementary materials. Raw data can be made available at reasonable request.