Legionella waterline colonization: detection of Legionella species in domestic, hotel and hospital hot water systems

A meta-analysis of Legionella pneumophila contamination in hospital water systems

BACKGROUND

Legionella pneumophila is a common cause of community-acquired pneumonia. We aimed to determine the pooled rates of L pneumophila contamination in the water environment of the hospital.

METHODS

We searched PubMed, Embase, Web of Science, Chinese National Knowledge Infrastructure, WangFang and Science Direct, The Cochrane Library, and Science Finder, for relevant studies published until December 2022. Stata 16.0 software was used to determine pooled contamination rates, publication bias, and subgroup analysis.

RESULTS

Forty-eight eligible articles with a total of 23,640 samples of water were evaluated, and the prevalence of L pneumophila was 41.6%. The results of the subgroup analysis showed that the pollution rate of L pneumophila in hot water (47.6%) was higher than that in other water bodies. The rates of L pneumophila contamination were higher in developed countries (45.2%), culture methods (42.3%), published between 1985 and 2015 (42.9%), and studies with a sample size of less than 100 (53.0%).

CONCLUSIONS

L pneumophila contamination in medical institutions is still very serious and should be paid attention to, especially in developed countries and hot water tanks.

Editorial: Special Issue: "Legionella pneumophila: A Microorganism with a Thousand Faces"

Legionella pneumophila is a microorganism that is able to contaminate the freshwater environment and, consequently, human-made water systems [...].

Environmental Monitoring of Legionella in Hospitals in the Campania Region: A 5-Year Study

Legionella is a pathogen that colonizes soils, freshwater, and building water systems. People who are most affected are those with immunodeficiencies, so it is necessary to monitor its presence in hospitals. The purpose of this study was to evaluate the presence of Legionella in water samples collected from hospitals in the Campania region, Southern Italy. A total of 3365 water samples were collected from January 2018 to December 2022 twice a year in hospital wards from taps and showers, tank bottoms, and air-treatment units. Microbiological analysis was conducted in accordance with the UNI EN ISO 11731:2017, and the correlations between the presence of Legionella and water temperature and residual chlorine were investigated. In total, 708 samples (21.0%) tested positive. The most represented species was L. pneumophila 2-14 (70.9%). The serogroups isolated were 1 (27.7%), 6 (24.5%), 8 (23.3%), 3 (18.9%), 5 (3.1%), and 10 (1.1%). Non-pneumophila Legionella spp. represented 1.4% of the total. Regarding temperature, the majority of Legionella positive samples were found in the temperature range of 26.0-40.9 °C. An influence of residual chlorine on the presence of the bacterium was observed, confirming that chlorine disinfection is effective for controlling contamination. The positivity for serogroups other than serogroup 1 suggested the need to continue environmental monitoring of Legionella and to focus on the clinical diagnosis of other serogroups.

Legionella monitoring results by water quality characteristics in a large public water system

Legionella, the causative agent of Legionnaires' disease, is an emerging concern for water utilities. Passaic Valley Water Commission (PVWC) is a public drinking water supplier, which provides treated surface water to approximately 800,000 customers in New Jersey. To evaluate the occurrence of Legionella in the PVWC distribution system, swab, first draw, and flushed cold water samples were collected from total coliform sites (n = 58) during a summer and winter sampling event. Endpoint PCR detection methods were combined with culture for Legionella detection. Among 58 total coliform sites during the summer, 17.2% (10/58) of first draw samples were positive for 16S and mip Legionella DNA markers and 15.5% (9/58) in flushed samples. Across both summer and winter sampling, a total of four out of 58 sites had low-level culture detection of Legionella spp. (0.5-1.6 CFU/mL) among first draw samples. Only one site had both a first and flush draw detection (8.5 CFU/mL and 1.1 CFU/mL) for an estimated culture detection frequency of 0% in the summer and 1.7% in the winter among flushed draw samples. No L. pneumophila was detected by culture. Legionella DNA detection was significantly greater in the summer than in the winter, and detection was greater in samples collected from areas treated with phosphate. No statistical difference was found between first draw and flush sample detection. Total organic carbon, copper, and nitrate were significantly associated with Legionella DNA detection.

Heterotrophic Plate Count Can Predict the Presence of Legionella spp. in Cooling Towers

Legionella pneumophila (Lp) colonizes aquatic environments and is a potential pathogen to humans, causing outbreaks of Legionnaire’s disease. It is mainly associated with contaminated cooling towers (CTs). Several regulations, including Spanish legislation (Sl), have introduced the analysis of heterotrophic plate count (HPC) bacteria and Legionella spp. (Lsp) in management plans to prevent and control Legionella outbreaks from CTs. The 2003 Sl for CTs (RD 865/2003) considered that concentrations of HPC bacteria ≤10,000 cfu/mL and of Lsp ≤100 cfu/L are safe; therefore, no action is required, whereas management actions should be implemented above these standards. We have investigated to what extent the proposed standard for HPC bacteria is useful to predict the presence of Lsp in cooling waters. For this, we analyzed Lsp and HPC concentrations, water temperature, and the levels of chlorine in 1376 water samples from 17 CTs. The results showed that in the 1138 water samples negative for Legionella spp. (LN), the HPC geometric mean was significantly lower (83 cfu/mL, p < 0.05) than in the positive Lsp. samples (135 cfu/mL). Of the 238 (17.3%) LP samples, 88.4% (210/238) were associated with values of HPC ≤10,000 cfu/mL and most of them showed HPC concentrations ≤100 (53.7%). In addition, a relatively low percentage of LP (28/238, 11.6%) samples were associated with HPC bacteria concentrations >10,000 cfu/mL, indicating that this standard does not predict the colonization risk for Legionella in the CTs studied. The present study has demonstrated that a threshold concentration ≤100 cfu/mL of HPC bacteria could better predict the higher concentration of Legionella in CTs, which will aid in preventing possible outbreaks.

Legionella colonisation in hot water systems in care homes from two Danish municipalities

Legionnaires' disease is a serious health risk among the elderly. Water systems in care homes are therefore of particular interest. We investigated the levels of culturable Legionella in the hot water systems in care homes in two Danish municipalities. Two hundred and sixty-eight water samples from 98 care homes were evaluated. Contents of culturable Legionella counts were calculated, and correlations between temperature and colony-forming units (CFU/L) were analysed. Seventy-seven and 81%, respectively, of the care homes were colonised with Legionella in the two municipalities. Most care homes had less than 1,000 CFU/L, but 13 and 16% had more than 10,000 CFU/L. When including first flush samples, 27% of the care homes in Municipality 1 had Legionella levels above 10,000 CFU/L. Temperatures of ≥50 °C in Municipality 1 and ≥55 °C in Municipality 2 correlated with low levels of Legionella. The content of Legionella colonies was significantly higher in care homes in Municipality 1. However, a significantly higher proportion of taps in Municipality 2 had Legionella colonies. In conclusion, temperatures should be raised to 55 °C to avoid high Legionella levels. Test procedures should be evaluated, and the regular use of taps and routine testing for Legionella should be taken into consideration.

Influence of Metal Concentration and Plumbing Materials on Legionella Contamination

Legionella colonization of water supply pipes is a significant public health problem. The objective of this work was to evaluate Legionella colonization in hotel hot water systems and to investigate the relationship between metal concentrations, piping materials (galvanized iron pipes and plastic pipes), and Legionella proliferation. Concentrations of calcium and magnesium ions and the presence of Legionella pneumophila were determined in a total of 108 water samples from the hot water systems of four hotels in Split-Dalmatia County over a 12-month period, and additional data on piping materials were collected. L. pneumophila was isolated in 23.1% of all samples-in 28.8% (15/52) of water samples from galvanized iron pipes and in 17.8% (10/56) of samples from plastic pipes. L. pneumophila serogroups 2-14 were isolated from all samples. This study found higher prevalence of L. pneumophila at higher concentrations of Ca and Mg ions (except for Mg and plastic pipes). The metal parts of the water supply may be important factors in Legionella contamination due to the possibility of lime scale or roughness of the pipes. Higher Ca and Mg ion concentrations increased the risk of Legionella colonization.

Environmental surveillance of Legionella in tourist facilities of the Balearic Islands, Spain, 2006 to 2010 and 2015 to 2018

BackgroundLegionnaires' disease is a respiratory illness often associated with hotels and travel. Spain is a major tourist destination and one of the European countries with most cases of Legionnaires' disease , both community- and travel-associated. However, the prevalence of Legionella in tourist facilities is unknown.AimThe present investigation aimed to survey the tourist facilities in the Balearic Islands, Spain, for Legionella prevalence.MethodsWe visited tourist facilities in the Balearic Islands in two different periods (2006-2010 and 2015-2018) and took water samples following national and international guidelines. Legionella was investigated by culture methods following international standards (ISO 11731:1998).ResultsWe evaluated 13,472 samples from 465 facilities. Bacteria of the Legionella genus were detected in 65.4% of the surveyed facilities. Contamination of the facilities was significantly higher during the second decade (54.5 vs 78.6%). The most frequent colonisers were L. pneumophila serogroup 2-14. We detected the pathogen in 15.9% and 6.9% of hot and cold water distribution systems samples, respectively. The Legionella contamination rate in cold water systems samples was higher when free chlorine levels were < 0.2 mg/L and at > 25 °C temperatures, while in the hot water systems samples, the contamination rate was higher at < 50 °C. Of the samples from hot tubs, 10.9% were contaminated.ConclusionLegionella prevalence in hotels in the Balearic Islands was high but the contamination rates depended on the installations. Corrective measures are still needed to improve Legionella control.

Four-Year Environmental Surveillance Program of Legionella spp. in One of Palermo’s Largest Hospitals

Legionella is a ubiquitous bacterium that lives in freshwater environments and colonizes human-made water systems. Legionella pneumophila is the most virulent species, and risk factors for Legionnaires’ disease include increasing age, smoking, chronic diseases, and immunodeficiency. For this reason, it is very important to assess and monitor hospital water systems in order to prevent legionellosis. We have monitored a large hospital in Palermo for four years. To determine the presence of microorganisms, according to national guidelines, we used the culture method, which is considered the gold standard for Legionella detection. Sampling was divided into five macro-areas, and a total of 251 samples were collected during the period of investigation, 49% of which were Legionella spp.-positive and 51% were Legionella spp.-negative. Positive samples with L. pneumophila. sgr 2-15 were most frequent in the Underground (55.6%, p = 0.0184), Medicine (42.9%, p = 0.0184) and Other (63.2%, p = 0.002) areas; while positive samples for L. pneumophila sgr 1 were less frequent in the Underground (0.0%, p = 0.0184) and Surgery areas (4.5%, p = 0.033), and for Legionella anisa, were less frequent in the Medicine (4.1%, p = 0.021), Oncohematology (0.0%, p = 0.0282), and Other (0.0%, p = 0.016) areas. Finally, no significant differences were observed among the areas for each isolate considered. The surveillance carried out in these years demonstrates the importance of monitoring, which allows us to analyze the conditions of hospital facilities and, therefore, prevent Legionella spp. infections.

The Presence of Opportunistic Premise Plumbing Pathogens in Residential Buildings: A Literature Review

Opportunistic premise plumbing pathogens (OPPP) are microorganisms that are native to the plumbing environment and that present an emerging infectious disease problem. They share characteristics, such as disinfectant resistance, thermal tolerance, and biofilm formation. The colonisation of domestic water systems presents an elevated health risk for immune-compromised individuals who receive healthcare at home. The literature that has identified the previously described OPPPs (Aeromonas spp., Acinetobacter spp., Helicobacter spp., Legionella spp., Methylobacterium spp., Mycobacteria spp., Pseudomonas spp., and Stenotrophomonas spp.) in residential drinking water systems were systematically reviewed. By applying the Preferred reporting items for systematic reviews and meta-analyses guidelines, 214 studies were identified from the Scopus and Web of Science databases, which included 30 clinical case investigations. Tap components and showerheads were the most frequently identified sources of OPPPs. Sixty-four of these studies detected additional clinically relevant pathogens that are not classified as OPPPs in these reservoirs. There was considerable variation in the detection methods, which included traditional culturing and molecular approaches. These identified studies demonstrate that the current drinking water treatment methods are ineffective against many waterborne pathogens. It is critical that, as at-home healthcare services continue to be promoted, we understand the emergent risks that are posed by OPPPs in residential drinking water. Future research is needed in order to provide consistent data on the prevalence of OPPPs in residential water, and on the incidence of waterborne homecare-associated infections. This will enable the identification of the contributing risk factors, and the development of effective controls.

Dynamics of the Microbial Community and Opportunistic Pathogens after Water Stagnation in the Premise Plumbing of a Building

In premise plumbing, microbial water quality may deteriorate under certain conditions, such as stagnation. Stagnation results in a loss of disinfectant residual, which may lead to the regrowth of microorganisms, including opportunistic pathogens. In the present study, microbial regrowth was investigated at eight faucets in a building over four seasons in one year. Water samples were obtained before and after 24 h of stagnation. In the first 100‍ ‍mL after stagnation, total cell counts measured by flow cytometry increased 14- to 220-fold with a simultaneous decrease in free chlorine from 0.17–0.36‍ ‍mg L^–1 to <0.02‍ ‍mg L^–1. After stagnation, total cell counts were not significantly different among seasons; however, the composition of the microbial community varied seasonally. The relative abundance of Pseudomonas spp. was dominant in winter, whereas Sphingomonas spp. were dominant in most faucets after stagnation in other seasons. Opportunistic pathogens, such as Legionella pneumophila, Mycobacterium avium, Pseudomonas aeruginosa, and Acanthamoeba spp., were below the quantification limit for real-time quantitative PCR in all samples. However, sequences related to other opportunistic pathogens, including L. feeleii, L. maceachernii, L. micdadei, M. paragordonae, M. gordonae, and M. haemophilum, were detected. These results indicate that health risks may increase after stagnation due to the regrowth of opportunistic pathogens.

A Tale of Four Danish Cities: Legionella pneumophila Diversity in Domestic Hot Water and Spatial Variations in Disease Incidence

Denmark has one of the highest Legionnaires' disease notification rates within Europe, averaging 4.7 cases per 100,000 population annually (2017 to 2020). The relatively high incidence of disease is not uniform across the country, and approximately 70% of all domestically acquired cases in Denmark are caused by Legionella pneumophila (LP) strains that are considered less virulent. The aim of this study was to investigate if colonization rates, levels of colonization, and/or types of LP present in hot water systems were associated with geographic differences in Legionnaires' disease incidence. Domestic water systems from four cities in Denmark were analyzed via culture and qPCR. Serogrouping and sequence typing was performed on randomly selected isolates. Single nucleotide polymorphism was used to identify clonal relationship among isolates from the four cities. The results revealed a high LP colonization rate from 68% to 87.5% among systems, composed primarily of non-serogroup 1. LP serogroup 1 reacting with the monoclonal antibody (MAb) 3/1 was not identified in any of the systems tested, while MAb 3/1 negative serogroup 1 strains were isolated from 10 systems (9.6%). We hypothesize that a combination of factors influences the incidence rate of LD in each city, including sequence type and serogroup distribution, colonization rate, concentration of Legionella in Pre-flush and Flush samples, and potentially building characteristics such as water temperature measured at the point of use.

Investigation of Legionella bacteria in water and cooling systems of a university in Turkey

Objectives: Colonization of Legionella in water systems is among the factors affecting the incidence of community and hospital-acquired pneumonia. In this study, it was aimed to investigate the presence of Legionella in the water and cooling systems of the inpatient services of the faculty of medicine hospital and the faculties of the university. Material and Methods: The presence of Legionella was investigated in 418 water and swab samples were taken from the water and cooling systems of the inpatient services of X University Faculty of Medicine Research and Practice Hospital and 11 faculties of the university between February-October 2020. Collected water and swab samples were inoculated into BCYE medium and identification at the species and serogroups by latex agglutination test. In addition, rpoB sequencing was used to confirm these isolates. Results: Legionella were isolated in four (4.1%) of the samples collected from the inpatient services of the hospital and in three (0.9%) of the samples collected from the faculties (n=321), in total seven (1.67%) samples. One of these isolates (14.3%) was grouped as L.pneumophila serogroup 2-14 and six (85.7%) as L.pneumophila serogroup 1 by latex agglutination test. Species identifications were consistent with sequence analysis results. Conclusion: The isolation of L.pneumophila in samples taken from inpatient services at a higher rate than in faculties poses a great risk. Although the detection rate of Legionella in our study was low, we think that regular disinfection, follow-up and inspection of water and cooling systems may be effective in reducing Legionella-related pneumonias.

Water Age Effects on the Occurrence and Concentration of Legionella Species in the Distribution System, Premise Plumbing, and the Cooling Towers

In this study, droplet digital PCR^TM (ddPCR^TM) was used to characterize total Legionella spp. and five specific Legionella species from source (groundwater) to exposure sites (taps and cooling towers). A total of 42–10 L volume water samples were analyzed during this study: 12 from a reservoir (untreated groundwater and treated water storage tanks), 24 from two buildings (influents and taps), and six from cooling towers, all part of the same water system. The approximate water age (time in the system) for all sample locations are as follows: ~4.5, 3.4, 9.2, 20.8, and 23.2 h (h) for the groundwater to the reservoir influent, reservoir influent to the reservoir effluent, reservoir effluent to building Fa (building names are abbreviated to protect the privacy of site location), building ERC and the cooling towers, respectively. Results demonstrated that gene copies of Legionella spp. (23S rRNA) were significantly higher in the cooling towers and ERC building (p < 0.05) relative to the reservoir and building Fa (closest to reservoir). Legionella spp. (23S rRNA) were found in 100% (42/42) of water samples at concentrations ranging from 2.2 to 4.5 Log10 GC/100 mL. More specifically, L. pneumophila was found in 57% (24/42) of the water samples, followed by L. bozemanii 52% (22/42), L. longbeachae 36% (15/42), L. micdadei 23% (10/42) and L. anisa 21% (9/42) with geometric mean concentrations of 1.7, 1.7, 1.4, 1.6 and 1.7 Log₁₀ GC/100 mL, respectively. Based on this study, it is hypothesized that water age in the distribution system and the premise-plumbing system as well as building management plays a major role in the increase of Legionella spp., (23S rRNA) and the diversity of pathogenic species found as seen in the influent, and at the taps in the ERC building—where the building water quality was most comparable to the industrial cooling towers. Other pathogenic Legionella species besides L.pneumophila are also likely amplifying in the system; thus, it is important to consider other disease relevant species in the whole water supply system—to subsequently control the growth of pathogenic Legionella in the built water environment.

Legionella: A Promising Supplementary Indicator of Microbial Drinking Water Quality in Municipal Engineered Water Systems

Opportunistic pathogens (OPs) are natural inhabitants and the predominant disease causative biotic agents in municipal engineered water systems (EWSs). In EWSs, OPs occur at high frequencies and concentrations, cause drinking-water-related disease outbreaks, and are a major factor threatening public health. Therefore, the prevalence of OPs in EWSs represents microbial drinking water quality. Closely or routinely monitoring the dynamics of OPs in municipal EWSs is thus critical to ensuring drinking water quality and protecting public health. Monitoring the dynamics of conventional (fecal) indicators (e.g., total coliforms, fecal coliforms, and Escherichia coli) is the customary or even exclusive means of assessing microbial drinking water quality. However, those indicators infer only fecal contamination due to treatment (e.g., disinfection within water utilities) failure and EWS infrastructure issues (e.g., water main breaks and infiltration), whereas OPs are not contaminants in drinking water. In addition, those indicators appear in EWSs at low concentrations (often absent in well-maintained EWSs) and are uncorrelated with OPs. For instance, conventional indicators decay, while OPs regrow with increasing hydraulic residence time. As a result, conventional indicators are poor indicators of OPs (the major aspect of microbial drinking water quality) in EWSs. An additional or supplementary indicator that can well infer the prevalence of OPs in EWSs is highly needed. This systematic review argues that Legionella as a dominant OP-containing genus and natural inhabitant in EWSs is a promising candidate for such a supplementary indicator. Through comprehensively comparing the behavior (i.e., occurrence, growth and regrowth, spatiotemporal variations in concentrations, resistance to disinfectant residuals, and responses to physicochemical water quality parameters) of major OPs (e.g., Legionella especially L. pneumophila, Mycobacterium, and Pseudomonas especially P. aeruginosa), this review proves that Legionella is a promising supplementary indicator for the prevalence of OPs in EWSs while other OPs lack this indication feature. Legionella as a dominant natural inhabitant in EWSs occurs frequently, has a high concentration, and correlates with more microbial and physicochemical water quality parameters than other common OPs. Legionella and OPs in EWSs share multiple key features such as high disinfectant resistance, biofilm formation, proliferation within amoebae, and significant spatiotemporal variations in concentrations. Therefore, the presence and concentration of Legionella well indicate the presence and concentrations of OPs (especially L. pneumophila) and microbial drinking water quality in EWSs. In addition, Legionella concentration indicates the efficacies of disinfectant residuals in EWSs. Furthermore, with the development of modern Legionella quantification methods (especially quantitative polymerase chain reactions), monitoring Legionella in ESWs is becoming easier, more affordable, and less labor-intensive. Those features make Legionella a proper supplementary indicator for microbial drinking water quality (especially the prevalence of OPs) in EWSs. Water authorities may use Legionella and conventional indicators in combination to more comprehensively assess microbial drinking water quality in municipal EWSs. Future work should further explore the indication role of Legionella in EWSs and propose drinking water Legionella concentration limits that indicate serious public health effects and require enhanced treatment (e.g., booster disinfection).

Legionella and other opportunistic pathogens in full-scale chloraminated municipal drinking water distribution systems

Water-based opportunistic pathogens (OPs) are a leading cause of drinking-water-related disease outbreaks, especially in developed countries such as the United States (US). Physicochemical water quality parameters, especially disinfectant residuals, control the (re)growth, presence, colonization, and concentrations of OPs in drinking water distribution systems (DWDSs), while the relationship between OPs and those parameters remain unclear. This study aimed to quantify how physicochemical parameters, mainly monochloramine residual concentration, hydraulic residence time (HRT), and seasonality, affected the occurrence and concentrations of four common OPs (Legionella, Mycobacterium, Pseudomonas, and Vermamoeba vermiformis) in four full-scale DWDSs in the US. Legionella as a dominant OP occurred in 93.8% of the 64 sampling events and had a mean density of 4.27 × 105 genome copies per liter. Legionella positively correlated with Mycobacterium, Pseudomonas, and total bacteria. Multiple regression with data from the four DWDSs showed that Legionella had significant correlations with total chlorine residual level, free ammonia concentration, and trihalomethane concentration. Therefore, Legionella is a promising indicator of water-based OPs, reflecting microbial water quality in chloraminated DWDSs. The OP concentrations had strong seasonal variations and peaked in winter and/or spring possibly because of reduced water usage (i.e., increased water stagnation or HRT) during cold seasons. The OP concentrations generally increased with HRT presumably because of disinfectant residual decay, indicating the importance of well-maintaining disinfectant residuals in DWDSs for OP control. The concentrations of Mycobacterium, Pseudomonas, and V. vermiformis were significantly associated with total chlorine residual concentration, free ammonia concentration, and pH and trihalomethane concentration, respectively. Overall, this study demonstrates how the significant spatiotemporal variations of OP concentrations in chloraminated DWDSs correlated with critical physicochemical water quality parameters such as disinfectant residual levels. This work also indicates that Legionella is a promising indicator of OPs and microbial water quality in chloraminated DWDSs.

Environmental surveillance of Legionella pneumophila in hot water systems of hotels in Morocco

OBJECTIVE

Environmental monitoring of Legionella in hot water systems of hotels in Morocco was performed during the period from January 2016 to April 2018. A total of 149 water samples from 118 different hotels were analyzed.

METHODS

A total of 149 water samples from 118 different hotels were analyzed. Possible risk factors were prospectively recorded, and data were analyzed in connection with building and plumbing systems characteristics. Data about building and risk factors were collected through a questionnaire survey.

RESULTS

Out of the 149 samples, 77(51.7%) were positive for L. pneumophila. Serological typing of the isolates revealed that 54 (70.1%) are L. pneumophila serogroup 2-15 and 23 (29.9%) are L. pneumophila serogroup 1. 56.8% of all buildings were colonized by L. pneumophila. Counts were over 1,000 CFU/L in 44%. Contamination was strongly correlated with temperature in the circulation, the age of the premise plumbing and the size of the building.

CONCLUSIONS

The results showed a relevant exposure to L. pneumophila in the community and the identified risk factors can serve as indicators for risk assessment and relevant actions.

Environmental Surveillance of Legionella spp. in an Italian University Hospital Results of 10 Years of Analysis

The occurrence of Legionella spp. in the water distribution systems of large hospitals and other healthcare facilities is considered particularly dangerous, due to the critical nature of the hospitalized patients. The aim of this study is to present a pluri-annual environmental surveillance in a large university hospital assessing the prevalence of Legionella spp. and underlining its variability over the years. The samples of water were collected in accordance with the Italian National Guidelines and the sampling sites considered in this study were selected favoring wards with very high-risk patients and with patients at increased risk. The laboratory analyzed a total of 305 water samples deriving from 24 different sampling points. Legionella spp. were detected in 39.4% of samples, the majority of which were contaminated by Legionella pneumophila serogroups 2–14 (68.7%). Statistically significant differences were found among different seasons with a linear trend in positive proportion from summer to spring. Several experimental interventions to prevent and reduce Legionella colonization were attempted, but there is no a definitive method for the complete eradication of this microorganism. The permanent monitoring of hospital water distribution systems is fundamental to preventing the potential risk of nosocomial Legionellosis and to implementing procedures to minimize the risk of Legionella spp. colonization.

The Bacterial Community Diversity of Bathroom Hot Tap Water Was Significantly Lower Than That of Cold Tap and Shower Water

Microbial drinking water quality in premise plumbing systems (PPSs) strongly affects public health. Bacterial community structure is the essential aspect of microbial water quality. Studies have elucidated the microbial community structure in cold tap water, while the microbial community structures in hot tap and shower water are poorly understood. We sampled cold tap, hot tap, and shower water from a simulated PPS monthly for 16 consecutive months and assessed the bacterial community structures in those samples via high-throughput sequencing of bacterial 16S rRNA genes. The total relative abundance of the top five most abundant phyla (Proteobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria, and Firmicutes) was greater than 90% among the 24 identified phyla. The most abundant families were Burkholderiaceae, Sphingomonadaceae, unclassified Alphaproteobacteria, unclassified Corynebacteriales, and Mycobacteriaceae. A multiple linear regression suggests that the bacterial community diversity increased with water temperature and the age of the simulated PPS, decreased with total chlorine residual concentration, and had a limited seasonal variation. The bacterial community in hot tap water had significantly lower Shannon and Inverse Simpson diversity indices (p < 0.05) and thus a much lower diversity than those in cold tap and shower water. The paradoxical results (i.e., diversity increased with water temperature, but hot tap water bacterial community was less diverse) were presumably because (1) other environmental factors made hot tap water bacterial community less diverse, (2) the diversity of bacterial communities in all types of water samples increased with water temperature, and (3) the first draw samples of hot tap water could have a comparable or even lower temperature than shower water samples and the second draw samples of cold tap water. In both a three-dimensional Non-metric multidimensional scaling ordination plot and a phylogenetic dendrogram, the samples of cold tap and shower water cluster and are separate from hot tap water samples (p < 0.05). In summary, the bacterial community in hot tap water in the simulated PPS had a distinct structure from and a much lower diversity than those in cold tap and shower water.

Assessing Hotel Employee Knowledge on Risk Factors and Risk Management Procedures for Microbial Contamination of Hotel Water Distribution Systems

Water management plans (WMPs), sometimes referred to as risk management plans (RMPs) or water safety plans (WSPs), are not mandatory for hotels in many countries of the world, including the US. As such, many hotel personnel are uninformed of WMPs and the precautions to take if their hotel water system is compromised. The purpose of this study was to identify hotel personnel's knowledge and practices of WMPs through a survey incorporating the Health Belief Model (HBM). Data were collected from 59 hotels within Fulton County, Georgia, USA, through a questionnaire, and questions were developed tailored to the HBM. Significant associations were found between the perceived susceptibility of contracting a waterborne illness and WMP for hotel personnel as well as between cues to action and having a WMP in general linear models (p ≤ 0.05). The study concludes that many key personnel are not aware of WMPs. Many hotel facilities do not have a plan in place, and some facilities are unaware of a current plan is in place. The study findings provide insight into the importance of WMPs and the risk factors associated with microbial contamination in a hotel building's plumbing system. Future research and potential law change should be emphasized to increase hotel employees' and owner's WMP knowledge.

Dynamic modelling of Legionella pneumophila thermal inactivation in water

A predictive mathematical model describing the effect of temperature on the inactivation of Legionella pneumophila in water was developed. Thermal inactivation of L. pneumophila was monitored under isothermal conditions (51 - 61°C). A primary log-linear model was fitted to the inactivation data and the estimated D values ranged from 0.23 to 25.31 min for water temperatures from 61 to 51°C, respectively. The effect of temperature on L. pneumophila inactivation was described using a secondary model, and the model parameters z value and D_ref (D-value at 55°C) were estimated at 5.54°C and 3.47 min, respectively. The developed model was further validated under dynamic temperature conditions mimicking various conditions of water thermal disinfection in plumbing systems. The results indicated that the model can satisfactorily predict thermal inactivation of the pathogen at dynamic temperature environments and effectively translate water temperature profiles to cell number reduction. The application of the model in combination with effective temperature monitoring could provide the basis of an integrated preventive approach for the effective control of L. pneumophila in plumbing systems.

Healthcare-Associated Legionella Disease: A Multi-Year Assessment of Exposure Settings in a National Healthcare System in the United States

Healthcare facilities are high-risk environments for Legionella disease (LD), including Legionnaires' disease, but transmission in these settings is often overlooked. We used the LD database at the U.S. Department of Veterans Affairs (VA) national healthcare system to assess the type of healthcare exposure for LD cases. Cases were extracted from the database for 1 September 2012 through 31 July 2019, focusing on cases with an overnight stay at a VA facility during the 10-day exposure window prior to symptom onset. Patient medical charts were reviewed for demographics and types of healthcare setting exposure(s). There were 99 LD cases in the cohort: 31.3% were classified as having definite VA exposure, 37.4% were classified as possible VA with inpatient exposure, and 31.3% were classified as possible VA with both inpatient and outpatient exposure. For definite VA LD cases, 67.7% had some type of exposure in the long-term care setting. While 63% of the 99 cases had exposure in the acute care setting only, both the long-term care and acute care settings contributed substantially to the total number of exposure days. A review of patient movement during the exposure period showed the variable and sometimes extensive use of the VA system, and it provides insights useful for epidemiologic investigations and potential preventive actions.

Legionellosis in Japan: A Self-inflicted Wound?

Legionellosis is a serious bacterial infection characterized by atypical pneumonia primarily due to infection with Legionella pneumophila, and bathing can be a potential cause of this infection. Legionellosis was first identified in 1977, and it is caused by Gram-negative bacteria belonging to the genus Legionella. Legionellosis remains an important public health threat, particularly in Japan, where the population is rapidly aging, thereby becoming more at risk of developing severe disease and accompanying life-threatening pneumonia. The bacteria are most commonly transmitted via the inhalation of contaminated aerosols produced and broadcast via water sprays, jets or mists. Infection can also occur via the aspiration of contaminated water or ice, or through inhalation of contaminated dust. Because the signs and symptoms of Legionnaires' disease (LD), as well as radiographic imaging are similar to pneumonia caused by other pathogens, a specific diagnostic test is required, such as a urine antigen detection test. Six clinical and laboratory parameters, a high body temperature, a non-productive cough, low serum sodium and platelet counts, and high lactate dehydrogenase (LDH) and c-reactive protein concentrations can be used to reliably predict the likelihood of LD. The first choices for chemotherapy are fluoroquinolone and macrolide antibiotic drugs. The main goals of LD prevention measures are 1) the prevention of microbial growth and biofilm formation, 2) the removal of all biofilm formed on equipment and in facilities, 3) minimizing aerosol splash and spread, and 4) minimizing bacterial contamination from external sources. It is apparent that, in Japan, where hot spring (onsen) bathing is common among aged people, strict regulations need to be in place - and enforced - to ensure that all Japanese onsens and spas provide a safe environment and undertake regular, effective infection control practices.

Biogeography and Environmental Drivers of Legionella pneumophila Abundance and Genotype Composition Across the West Bank: Relevance of a Genotype-Based Ecology for Understanding Legionella Occurrence

The West Bank can be considered as a high-risk area for Legionella prevalence in drinking water due to high ambient temperature, intermittent water supply, frequent pressure loss, and storage of drinking water in roof containers. To assess occurrence of Legionella species, especially L. pneumophila, in the drinking water of the West Bank, the drinking water distribution systems of eight hospitals were sampled over a period of 2.3 years covering the seasonal cycle and the major geographic regions. To gain insight into potential environmental drivers, a set of physico-chemical and microbiological parameters was recorded. Sampling included drinking water and biofilm analyzed by culture and PCR-based methods. Cultivation led to the isolation of 180 strains of L. pneumophila that were genotyped by Multi-Locus Variable Number of Tandem Repeat Analysis (MLVA). Surprisingly, the abundance of culturable L. pneumophila was low in drinking water of the sampling sites, with only three out of eight sites where Legionella was observed at all (range: 30–500 CFU/Liter). By contrast, biofilm and PCR-based analyses showed a higher prevalence. Statistical analyses with physico-chemical parameters revealed a decrease of L. pneumophila abundance for water and biofilm with increasing magnesium concentrations (>30 mg/L). MLVA-genotype analysis of the L. pneumophila isolates and their spatial distribution indicated three niches characterized by distinct physico-chemical parameters and inhabited by specific consortia of genotypes. This study provides novel insights into mechanisms shaping L. pneumophila populations and triggering their abundance leading to an understanding of their genotype-specific niches and ecology in support of improved prevention measures.

Critical Review: Propensity of Premise Plumbing Pipe Materials to Enhance or Diminish Growth of Legionella and Other Opportunistic Pathogens

Growth of Legionella pneumophila and other opportunistic pathogens (OPs) in drinking water premise plumbing poses an increasing public health concern. Premise plumbing is constructed of a variety of materials, creating complex environments that vary chemically, microbiologically, spatially, and temporally in a manner likely to influence survival and growth of OPs. Here we systematically review the literature to critically examine the varied effects of common metallic (copper, iron) and plastic (PVC, cross-linked polyethylene (PEX)) pipe materials on factors influencing OP growth in drinking water, including nutrient availability, disinfectant levels, and the composition of the broader microbiome. Plastic pipes can leach organic carbon, but demonstrate a lower disinfectant demand and fewer water chemistry interactions. Iron pipes may provide OPs with nutrients directly or indirectly, exhibiting a high disinfectant demand and potential to form scales with high surface areas suitable for biofilm colonization. While copper pipes are known for their antimicrobial properties, evidence of their efficacy for OP control is inconsistent. Under some circumstances, copper's interactions with premise plumbing water chemistry and resident microbes can encourage growth of OPs. Plumbing design, configuration, and operation can be manipulated to control such interactions and health outcomes. Influences of pipe materials on OP physiology should also be considered, including the possibility of influencing virulence and antibiotic resistance. In conclusion, all known pipe materials have a potential to either stimulate or inhibit OP growth, depending on the circumstances. This review delineates some of these circumstances and informs future research and guidance towards effective deployment of pipe materials for control of OPs.

Required water temperature in hotel plumbing to control Legionella growth

Legionella spp. occurring in hotel hot water systems, in particular Legionella pneumophila, are causing serious pneumonic infections, and water temperature is a key factor to control their occurrence in plumbing systems. We performed a systematic review and meta-analyses of the available evidence on the association between water temperature and Legionella colonization to identify the water temperature in hotel hot water systems required for control of Legionella. Qualitative synthesis and quantitative analysis were performed on 13 studies that met our inclusion criteria to identify the effect of temperature. The Receiver Operating Characteristic (ROC) curve identified 55 °C as a cutoff point for hotel hot water temperature with an Area Under the Curve (AUC) value of 0.914. The odds ratios (OR) for detecting Legionella at temperatures >55 °C compared to lower temperatures from a meta-analysis of three studies was 0.17 [95% CI: 0.11, 0.25], which indicates a strong negative association between temperature and Legionella colonization. A logistic regression on results from multiple studies using both molecular and culture methods found a temperature of 59 °C associated with an 8% probability of detectable Legionella. Only two studies reported sufficiently detailed data to allow a model of concentration vs. temperature to be fit, and this model was not statistically significant. Additional research or more detailed reporting of existing datasets is required to assess if Legionella growth can be limited below particular concentration targets at different temperatures.

A Snapshot of the Prevalence and Molecular Diversity of Legionella pneumophila in the Water Systems of Israeli Hotels

Exposure to Legionella spp. contaminated aerosols in hotel settings confers risk for travel-associated Legionnaire’s disease (TALD). In this study, we investigated the prevalence of Legionella contamination and its molecular diversity in hotels and resorts across Israel. The study was comprised of a convenience sample of water systems from 168 hotels and resorts countrywide, routinely inspected between March 2015 and February 2017. Isolation and quantitation of Legionella were performed in a water laboratory using the ISO 11731 method. The distribution of Legionella isolates was analyzed according to geography and source. The genetic diversity of a subset of isolates was analyzed by sequence-based typing (SBT) at the National Reference Laboratory for Legionella and compared to the national database. Out of 2830 samples tested, 470 (17%) obtained from 102 different premises (60% of hotels) were positive for Legionella spp. In 230 samples (49% of all positive, 8% of total samples), accounting for 37% of hotels, Legionella spp. counts exceeded the regulatory threshold of 1000 CFU/L. The most frequently contaminated water sources were cooling towers (38%), followed by faucets, hot tubs, water lines, and storage tanks (14–17% each). Furthermore, 32% and 17% of samples obtained from cooling towers and hot tubs, respectively, exceeded the regulatory thresholds. SBT was performed on 78 strains and revealed 27 different sequence types (STs), including two novel STs. The most prevalent STs found were ST1 (26%), ST87 (10%), ST93 (6%), and ST461 and ST1516 (5% each). Several L. pneumophila STs were found to be limited to certain geographical regions. This is the first study to investigate the prevalence and diversity of Legionella in hotels and resorts in Israel during non-outbreak environmental inspections. These findings will inform risk assessment, surveillance, and control measures of TALD.

Water Quality as a Predictor of Legionella Positivity of Building Water Systems

Testing drinking water systems for the presence of Legionella colonization is a proactive approach to assess and reduce the risk of Legionnaires’ disease. Previous studies suggest that there may be a link between Legionella positivity in the hot water return line or certain water quality parameters (temperature, free chlorine residual, etc.) with distal site Legionella positivity. It has been suggested that these measurements could be used as a surrogate for testing for Legionella in building water systems. We evaluated the relationship between hot water return line Legionella positivity and other water quality parameters and Legionella colonization in premise plumbing systems by testing 269 samples from domestic cold and hot water samples in 28 buildings. The hot water return line Legionella positivity and distal site positivity only demonstrated a 77.8% concordance rate. Hot water return line Legionella positivity compared to distal site positivity had a sensitivity of 55% and a specificity of 96%. There was poor correlation and a low positive predictive value between the hot water return line and distal outlet positivity. There was no correlation between Legionella distal site positivity and total bacteria (heterotrophic plate count), pH, free chlorine, calcium, magnesium, zinc, manganese, copper, temperature, total organic carbon, or incoming cold-water chlorine concentration. These findings suggest that hot water return line Legionella positivity and other water quality parameters are not predictive of distal site positivity and should not be used alone to determine the building’s Legionella colonization rate and effectiveness of water management programs.

Legionella pneumophila as a Health Hazard to Miners: A Pilot Study of Water Quality and QMRA

Legionella pneumophila (L. pneumophila), the causative agent of legionellosis, is an aquatic bacterium that grows in warm water. Humans are only presented with a health risk when aerosolized water containing L. pneumophila is inhaled. In mining operations, aerosolized water is used as dust control and as part of the drilling operations, a currently ignored exposure route. This study characterized L. pneumophila concentrations in the mine's non-potable water and the relationship between L. pneumophila and chlorine concentrations. These concentrations informed a quantitative microbial risk assessment (QMRA) model to estimate the infection risk to miners exposed to aerosolized water containing L. pneumophila. Fourteen water samples were collected from seven locations at a mine and analyzed for temperature, pH, chlorine, and L. pneumophila serogroup. Most samples (93%) tested positive for L. pneumophila cells. The faucet from the sprinkler system on the adit level (entrance to the underground mine levels) showed the highest concentration of L. pneumophila (8.35 × 104 MPN/L). Disability adjusted life years (DALYs) were estimated in the QMRA model and showed that the risk for all miners was significantly lower (p < 0.0001) with the ventilation system on than when the system was off. Our study showed that the use of a ventilation system at the adit level of the mine reduced the risk of infection with aerosolized L. pneumophila.

Environmental Surveillance of Legionellosis within an Italian University Hospital-Results of 15 Years of Analysis

Legionnaires' disease is normally acquired by inhalation of legionellae from a contaminated environmental source. Water systems of large and old buildings, such as hospitals, can be contaminated with legionellae and therefore represent a potential risk for the hospital population. In this study, we demonstrated the constant presence of Legionella in water samples from the water system of a large university hospital in Messina (Sicily, Italy) consisting of 11 separate pavilions during a period of 15 years (2004⁻2018). In total, 1346 hot water samples were collected between January 2004 and December 2018. During this period, to recover Legionella spp. from water samples, the standard procedures reported by the 2000 Italian Guidelines were adopted; from May 2015 to 2018 Italian Guidelines revised in 2015 (ISS, 2015) were used. Most water samples (72%) were positive to L. pneumophila serogroups 2⁻14, whereas L. pneumophila serogroup 1 accounted for 18% and non-Legionellapneumophila spp. Accounted for 15%. Most of the positive samples were found in the buildings where the following critical wards are situated: (Intensive Care Unit) ICU, Neurosurgery, Surgeries, Pneumology, and Neonatal Intensive Unit Care. This study highlights the importance of the continuous monitoring of hospital water samples to prevent the potential risk of nosocomial legionellosis.

One-year survey of opportunistic premise plumbing pathogens and free-living amoebae in the tap-water of one northern city of China

In this study, qPCR was used to quantify opportunistic premise plumbing pathogens (OPPPs) and free-living amoebae in 11 tap water samples collected over four seasons from a city in northern China. Results demonstrated that the average numbers of gene copies of Legionella spp. and Mycobacterium spp. were significantly higher than those of Aeromonas spp. (p < 0.05). Legionella spp. and Mycobacterium spp. were 100% (44/44) positively detected while P. aeruginosa and Aeromonas spp. were 79.54% (35/44) and 77.27% (34/44) positively detected. Legionella pneumophila was only detected in 4 samples (4/44), demonstrating its occasional occurrence. No Mycobacterium avium or Naegleria fowleri was detected in any of the samples. The average gene copy numbers of target OPPPs were the highest in summer, suggesting seasonal prevalence of OPPPs. Average gene copy numbers of OPPPs in the taps of low-use-frequency were higher than in taps of high-use-frequency, but the difference was not significant for some OPPPs (p > 0.05). Moderate negative correlations between the chlorine concentration and the gene copy numbers of OPPPs were observed by Spearman analysis (r_s ranged from -0.311 to -0.710, p < 0.05). However, no significant correlations existed between OPPPs and AOC, BDOC, or turbidity. Moderate positive correlations were observed between the target microorganisms, especially for Acanthamoeba spp., through Spearman analysis (p < 0.05). Based on our studies, it is proposed that disinfectant concentration, season, taps with different-use frequency, OPPP species, and potential microbial correlations should be considered for control of OPPPs in tap water.

Prevalence of Legionella in retirement homes and group homes water distribution systems

BACKGROUND

Although historically the focus has been placed above all on hospital infections and travel-associated outbreaks, most of the cases of Legionella infection are sporadic and occur in community-dwellers.

OBJECTIVES

To evaluate the presence and load of Legionella in hot water systems of non-healthcare facilities that host closed communities. Furthermore, we tried to verify the association between Heterotrophic Plate Counts (HPCs) and presence of Legionella.

METHODS

We collected hot water and biofilm samples from the showerheads of retirement homes and group homes. Samples were tested by culture method for the presence of Legionella. Confirmation and identification were carried out through Latex test and PCR. We determined the HPCs at 22 and 37 °C by the pour plate method. Statistics performed through STATA.

RESULTS

We collected 140 hot water and biofilm samples, 95 from 26 retirement homes and 35 from 9 group homes. Legionella was found in 36.8% samples collected from retirement homes and only in 10.3% group homes' samples (p = 0.01). Legionella was identified more frequently in water than in biofilm (29.8% vs 16.9%); just in one case the pathogen was found in the biofilm only. L. pneumophila sg 1 was the pathogen more frequently isolated (65.8%), with an average load of 2720 CFU/L (SD = 8393 CFU/L). We have often noticed a high microbial contamination (67% of HPCs >200 CFU/mL) and identified a higher prevalence of Legionella for intermediate values of HPC 22 °C (p = 0.011). 32% of people hosted in retirement homes were exposed to Legionella.

CONCLUSIONS

Colonization of water-systems of retirement homes and group homes is anything but occasional, and in our survey it mainly affects the former, moreover often due to L. pneumophila sg 1. The search for the pathogen in the biofilm has proved to be of little use. The relationship between HPC and Legionella deserves further studies.

Legionella Colonization of Hotel Water Systems in Touristic Places of Greece: Association with System Characteristics and Physicochemical Parameters

This study aimed to assess the colonization of hotel water systems in central Greece and Corfu by Legionella, and to investigate the association between physicochemical parameters and Legionella colonization. Standardized hygiene inspection was conducted in 51 hotels, and 556 water samples were analyzed for Legionella spp. Free chlorine concentration, pH, hardness, conductivity, and trace metals were defined in cold water samples. The results of inspections and chemical analyses were associated with the microbiological results using univariate and logistic regression analysis. According to the score of the checklist used for the inspections, 17.6% of the hotels were classified as satisfactory, 15.7% as adequate, and 66.7% as unsatisfactory. Moreover, 74.5% of the hotels were colonized by Legionella spp. and 31.4% required remedial measures according to the European guidelines. Legionella spp. were isolated in 28% of the samples. Unsatisfactory results of inspections were associated with Legionella presence (relative risk (RR) = 7.67, p-value = 0.043). In hot-water systems, <50 °C temperatures increased the risk of Legionella colonization (RR = 5.36, p-value < 0.001). In cold-water systems, free chlorine concentration <0.375 mg/L (odds ratio (OR) = 9.76, p-value = 0.001), pH ≥ 7.45 (OR = 4.05, p-value = 0.007), and hardness ≥321 mgCaCO₃/L (OR = 5.63, p-value = 0.003) increased the risk, whereas copper pipes demonstrated a protective role (OR = 0.29, p-value = 0.0024). The majority of the hotels inspected were colonized with Legionella. Supplementary monitoring of the risk factors that were identified should be considered.

Risk of infection from Legionella associated with spray irrigation of reclaimed water

Legionella pneumophila has been detected in reclaimed water used for spray irrigation of turfgrass in public parks and golf courses. This study determined the risks of infection from exposure to various levels of Legionella in reclaimed waters considering: the method of spray application; and the duration and frequency of exposure. Evaluation of these factors resulted in a risk of infection greater than 1:10,000 for several scenarios when the number of Legionella in the reclaimed water exceeded 1000 colony-forming units (CFU) per ml. Most current guidelines for control of Legionella in distribution systems recommend that increased monitoring or remedial action be taken when Legionella levels exceed 1000 to 10,000 CFU/ml. Based upon our risk assessment, these guidelines seem appropriate for reclaimed water systems where spray irrigation is practiced.

Legionellosis Associated with Recreational Waters: A Systematic Review of Cases and Outbreaks in Swimming Pools, Spa Pools, and Similar Environments

Legionella spp. is widespread in many natural and artificial water systems, such as hot water distribution networks, cooling towers, and spas. A particular risk factor has been identified in the use of whirlpools and hot tubs in spa facilities and public baths. However, there has been no systematic synthesis of the published literature reporting legionellosis cases or outbreaks related to swimming/spa pools or similar environments used for recreational purposes (hot springs, hot tubs, whirlpools, natural spas). This study presents the results of a systematic review of the literature on cases and outbreaks associated with these environments. Data were extracted from 47 articles, including 42 events (17 sporadic cases and 25 outbreaks) and 1079 cases, 57.5% of which were diagnosed as Pontiac fever, without any deaths, and 42.5% were of Legionnaires' disease, with a fatality rate of 6.3%. The results are presented in relation to the distribution of Legionella species involved in the events, clinical manifestations and diagnosis, predisposing conditions in the patients, favourable environmental factors, and quality of the epidemiological investigation, as well as in relation to the different types of recreational water sources involved. Based on the epidemiological and microbiological criteria, the strength of evidence linking a case/outbreak of legionellosis with a recreational water system was classified as strong, probable, and possible; in more than half of the events the resulting association was strong.

Valuation of Water and Emissions in Energy Systems

Pricing, incentives, and economic penalties (monetization) are common approaches to control and improve water usage and total direct greenhouse gas emissions (externalities) of energy and other industrial systems. We discuss that homogenous pricing for externalities provides limited flexibility for controlling and improving environmental impacts as different systems are affected differently by externalities. We use trade-off analysis and scalarization techniques to determine marginal prices for water and carbon by taking into account the actual physical and technical limits, stakeholders, and real-time conditions of the system at hand. We demonstrate that high water and emission prices might be needed to control and improve the current system of fixed price for externalities. In addition, a combined heat and power (CHP) system providing hot water and electricity to a real residential building complex is undertaken as case study to demonstrate and describe these concepts. For this CHP system, we found that carbon prices should be increased by a factor of 14 and water prices by a factor of 217 to achieve an optimal compromise between cost, water use, and emissions. Our results point towards the need to consider alternative pricing schemes such as resource bidding (as is done with electricity) that better capture technology trade-offs and push systems towards their efficiency limits.

Presence of Legionella spp. in Hot Water Networks of Different Italian Residential Buildings: A Three-Year Survey

Although the European reports highlight an increase in community-acquired Legionnaires’ disease cases, the risk of Legionella spp. in private houses is underestimated. In Pisa (Italy) we performed a three-year survey on Legionella presence in 121 buildings with an independent hot water production (IB); 64 buildings with a central hot water production (CB); and 35 buildings with a solar thermal system for hot water production (TB). From all the 220 buildings Legionella spp. was researched in two hot water samples collected either at the recirculation point or on the first floor and on the last floor, while the potable water quality was analysed in three cold water samples collected at the inlet from the aqueduct network, at the exit from the autoclave, and at the most remote tap. Legionella pneumophila sg1, Legionella pneumophila sg2–16, and non-pneumophila Legionella species were detected in 26% of the hot water networks, mostly in CB and TB. In these buildings we detected correlations between the presence of Legionella and the total chlorine concentration decrease and/or the increase of the temperature. Cold water resulted free from microbiological hazards, with the exception of Serratia liquefaciens and Enterobacter cloacae isolated at the exit from two different autoclaves. We observed an increase in total microbial counts at 22 °C and 37 °C between the samples collected at the most remote taps compared to the ones collected at the inlet from the aqueduct. The study highlights a condition of potential risk for susceptible categories of population and supports the need for measures of risk assessment and control.

Distribution System Operational Deficiencies Coincide with Reported Legionnaires' Disease Clusters in Flint, Michigan

We hypothesize that the increase in reported Legionnaires' disease from June 2014 to November 2015 in Genesee County, MI (where Flint is located) was directly linked to the switch to corrosive Flint River water from noncorrosive Detroit water from April 2014 to October 2015. To address the lack of epidemiological data linking the drinking water supplies to disease incidence, we gathered physiochemical and biological water quality data from 2010 to 2016 to evaluate characteristics of the Flint River water that were potentially conducive to Legionella growth. The treated Flint River water was 8.6 times more corrosive than Detroit water in short-term testing, releasing more iron, which is a key Legionella nutrient, while also directly causing disinfectant to decay more rapidly. The Flint River water source was also 0.8-6.7 °C warmer in summer months than Detroit water and exceeded the minimum Legionella growth temperature of 20 °C more frequently (average number of days per year for Detroit was 63 versus that for the Flint River, which was 157). The corrosive water also led to 1.3-2.2 times more water main breaks in 2014-2015 compared to 2010-2013; such disruptions have been associated with outbreaks in other locales. Importantly, Legionella spp. and Legionella pneumophila decreased after switching back to Detroit water, in terms of both gene markers and culturability, when August and October 2015 were compared to November 2016.

Differential expression of virulence genes in Legionella pneumophila growing in Acanthamoeba and human monocytes

Legionella pneumophila, the causative agent of Legionnaires’ disease, is widely distributed throughout natural and artificial water systems and can replicate in macrophages and amoebae. Amoebae are the natural hosts of L. pneumophila, whereas macrophages are incidentally infected. The life cycle of L. pneumophila comprises a replicative phase within the Legionella-containing vacuole (LCV) and a transmissive phase during which bacterial cells become motile and are released via killing of the host. Although the host death mechanisms induced by L. pneumophila have been studied, the expression patterns of related L. pneumophila genes have not been reported. The present study compared the expression patterns of host cell death-associated genes in L. pneumophila grown in the human monocytic cell line THP-1 and Acanthamoeba castellanii. Notably, when L. pneumophila was grown in THP-1, expression of the gene flaA, which is involved in the induction of pyroptosis, was downregulated during the course of infection. In contrast, sdhA associated indirectly with host death, was upregulated. Expression of the genes vipD and sidF, which are involved in the induction and suppression of apoptosis, changed by less than 2-fold. Notably, a lower percentage of pyroptotic cells was observed among infected THP-1 cells relative to uninfected cells, and the latter exhibited stronger expression of caspase-1. A different pattern was observed when L. pneumophila was grown in A. castellanii: flaA and vipD were activated, whereas sdhA and sidF were downregulated during the later stage of replication. The percentage of non-viable (annexin-V⁺ PI⁺ or annexin-V⁺PI⁻) A. castellanii organisms increased with Legionella infection, and the expression of metacaspase-1, which is involved in encystation was up-regulated at late infection time. In summary, L. pneumophila can multiply intracellularly in both amoebae and macrophages to induce cell death and secondary infection, and this characteristic is essential for its survival in water and the lungs. The gene expression profiles observed in this study indicated the increased cytotoxicity of L. pneumophila in A. castellanii, suggesting an increased adaptation of Legionella to this host.

Interactive effects of temperature, organic carbon, and pipe material on microbiota composition and Legionella pneumophila in hot water plumbing systems

BACKGROUND

Several biotic and abiotic factors have been reported to influence the proliferation of microbes, including Legionella pneumophila, in hot water premise plumbing systems, but their combined effects have not been systematically evaluated. Here, we utilize simulated household water heaters to examine the effects of stepwise increases in temperature (32-53 °C), pipe material (copper vs. cross-linked polyethylene (PEX)), and influent assimilable organic carbon (0-700 μg/L) on opportunistic pathogen gene copy numbers and the microbiota composition, as determined by quantitative polymerase chain reaction and 16S rRNA gene amplicon sequencing.

RESULTS

Temperature had an overarching influence on both the microbiota composition and L. pneumophila numbers. L. pneumophila peaked at 41 °C in the presence of PEX (1.58 × 105 gene copies/mL). At 53 °C, L. pneumophila was not detected. Several operational taxonomic units (OTUs) persisted across all conditions, accounting for 50% of the microbiota composition from 32 to 49 °C and 20% at 53 °C. Pipe material most strongly influenced microbiota composition at lower temperatures, driven by five to six OTUs enriched with each material. Copper pipes supported less L. pneumophila than PEX pipes (mean 2.5 log10 lower) at temperatures ≤ 41 °C, but showed no difference in total bacterial numbers. Differences between pipe materials diminished with elevated temperature, probably resulting from decreased release of copper ions. At temperatures ≤ 45 °C, influent assimilable organic carbon correlated well with total bacterial numbers, but not with L. pneumophila numbers. At 53 °C, PEX pipes leached organic carbon, reducing the importance of dosed organic carbon. L. pneumophila numbers correlated with a Legionella OTU and a Methylophilus OTU identified by amplicon sequencing.

CONCLUSIONS

Temperature was the most effective factor for the control of L. pneumophila, while microbiota composition shifted with each stepwise temperature increase. While copper pipe may also help shape the microbiota composition and limit L. pneumophila proliferation, its benefits might be constrained at higher temperatures. Influent assimilable organic carbon affected total bacterial numbers, but had minimal influence on opportunistic pathogen gene numbers or microbiota composition. These findings provide guidance among multiple control measures for the growth of opportunistic pathogens in hot water plumbing and insight into the mediating role of microbial ecological factors.

Factors Shaping the Human Exposome in the Built Environment: Opportunities for Engineering Control

The "exposome" is a term describing the summation of one's lifetime exposure to microbes and chemicals. Such exposures are now recognized as major drivers of human health and disease. Because humans spend ∼90% of their time indoors, the built environment exposome merits particular attention. Herein we utilize an engineering perspective to advance understanding of the factors that shape the built environment exposome and its influence on human wellness and disease, while simultaneously informing development of a framework for intentionally controlling the exposome to protect public health. Historically, engineers have been focused on controlling chemical and physical contaminants and on eradicating microbes; however, there is a growing awareness of the role of "beneficial" microbes. Here we consider the potential to selectively control the materials and chemistry of the built environment to positively influence the microbial and chemical components of the indoor exposome. Finally, we discuss research gaps that must be addressed to enable intentional engineering design, including the need to define a "healthy" built environment exposome and how to control it.

Occupational risk for Legionella infection among dental healthcare workers: meta-analysis in occupational epidemiology

OBJECTIVE

The occupational risk for Legionella infection among dental healthcare workers (DHCWs) is conjectured because of the risk of routine inhalation of potentially contaminated aerosols produced by the dental instruments. Nevertheless, occupational epidemiology studies are contrasting. This meta-analysis assessed the level of scientific evidence regarding the relative occupational risk for Legionella infection among DHCWs.

METHODS

Literature search was performed without time and language restrictions, using broad data banks (PubMed, Scopus, Web of Science, GOOGLE Scholar) and generic keywords ('legionella' AND 'dent*'). Analytical cross-sectional studies comparing prevalence of high serum Legionella antibody levels in DHCWs and occupationally unexposed individuals were considered. The relative occupational risk was assessed through prevalence ratio (PR) with 95% CI. Between-study heterogeneity was assessed (Cochran's Q test) and was used to choose the meta-analytic method. Study quality (modified Newcastle-Ottawa Scale) and publication bias (Begg and Mazumdar's test, Egger and colleagues' test, trim and fill R₀ method) were assessed formally and considered for the sensitivity analysis. Sensitivity analysis to study inclusion, subgroup analyses (dental staff categories; publication year, before vs after 1998, ie, 5 years after the release by the Centers for Disease Control and Prevention of the infection control guidelines in dental healthcare setting) were performed.

RESULTS

Seven studies were included (2232 DHCWs, 1172 occupationally unexposed individuals). No evidence of publication bias was detected. The pooled PR estimate was statistically non-significant at 95% level (1.7; 95% CI 0.8 to 3.2), study-quality adjustment did not change the PR considerably (PR, 1.5; 95% CI 0.5 to 4.1). PR was statistically significant before 1998 and no longer significant after 1998. Subgroup analysis according to DHCW categories was inconclusive.

CONCLUSIONS

There is no scientific evidence that DHCWs are at high occupational risk. The differences between former and recent studies could be due to different characteristics of municipal water systems and the infection control guideline dissemination.