Legionella Growth Research Articles

Two Outbreaks of Legionnaires Disease Associated with Outdoor Hot Tubs for Private Use - Two Cruise Ships, November 2022-July 2024.

Legionnaires disease is a serious pneumonia caused by Legionella bacteria. During November 2022-June 2024, CDC was notified of 12 cases of Legionnaires disease among travelers on two cruise ships; eight on cruise ship A and four on cruise ship B. CDC, in collaboration with the cruise lines, initiated investigations to ascertain the potential sources of on-board exposure after notification of the second potentially associated case for each ship. Epidemiologic data collected from patient interviews and environmental assessment and sampling results identified private hot tubs on selected cabin balconies as the most likely exposure source. To minimize Legionella growth, both cruise lines modified the operation and maintenance of these devices by removing the heating elements, draining water between uses, and increasing the frequency of hyperchlorination and cleaning. Hot tubs offer favorable conditions for Legionella growth and transmission when maintained and operated inadequately, regardless of location. Private hot tubs on cruise ships are not subject to the same maintenance requirements as are public hot tubs in common areas. Given the range of hot tub-type devices offered as amenities across the cruise industry, to reduce risk for Legionella growth and transmission, it is important for cruise ship water management program staff members to inventory and assess private balcony hot tubs and adapt public hot tub maintenance and operations protocols for use on private outdoor hot tubs.

Statistical analysis of parameters affecting Legionella and total cell growth in premise plumbing systems within buildings: A field study based on an empirical data set

During the storage and distribution of water in buildings, the excessive growth of pathogens can deteriorate the quality of drinking water. This study aims to investigate the factors influencing this growth and propose technical measures for prevention. The analysis is based on an empirical data set comprising 1361 samples from 204 domestic premise plumbing systems. In 14 systems, ultrafiltration plants were installed as microbiological barriers. Legionella cultivation and flow cytometry were used to determine microbiological properties. The study identified elevated total cell counts in tapping valves and pipe end lines in numerous premise plumbing systems, indicating prolonged water stagnation prior to sampling, which facilitates microbiological growth. Higher contamination rates were observed in these systems, with peripheral taps often being contaminated in lieu of the entire system. These systems were classified as microbiologically unstable due to the relevantly higher total cell numbers at hot water taps compared to the hot water tank (>25%). Furthermore, these systems exhibited a Legionella contamination rate that was 22.3% higher than in microbiologically stable systems. In some cases, peripheral contaminations may not accurately represent the entire premise plumbing system. Increasing the discard volume during sampling from 1 L to 3–5 L could provide more precise results during standard testing. Legionella species were primarily detected in the first 1 L of water after tap activation. Additionally, statistically significant relationships were observed between direct temperature and total cell number, as well as between the presence of ultrafiltration and total cell numbers at cold water taps.

Factors Associated with Legionella Detection in the Water Systems of National Lodging Organization Facilities with Water Management Programs in the United States.

A better understanding of risk factors and the predictive capability of water management program (WMP) data in detecting Legionella are needed to inform the efforts aimed at reducing Legionella growth and preventing outbreaks of Legionnaires' disease. Using WMPs and Legionella testing data from a national lodging organization in the United States, we aimed to (1) identify factors associated with Legionella detection and (2) assess the ability of WMP disinfectant and temperature metrics to predict Legionella detection. We conducted a logistic regression analysis to identify WMP metrics associated with Legionella serogroup 1 (SG1) detection. We also estimated the predictive values for each of the WMP metrics and SG1 detection. Of 5435 testing observations from 2018 to 2020, 411 (7.6%) had SG1 detection, and 1606 (29.5%) had either SG1 or non-SG1 detection. We found failures in commonly collected WMP metrics, particularly at the primary test point for total disinfectant levels in hot water, to be associated with SG1 detection. These findings highlight that establishing and regularly monitoring water quality parameters for WMPs may be important for preventing Legionella growth and subsequent disease. However, while unsuitable water quality parameter results are associated with Legionella detection, this study found that they had poor predictive value, due in part to the low prevalence of SG1 detection in this dataset. These findings suggest that Legionella testing provides critical information to validate if a WMP is working, which cannot be obtained through water quality parameter measurements alone.

Selectively Isolation and Molecular Identification by dnaJ Gene of Legionella pneumophila Found in Various Water Sources in Dhaka, Bangladesh

Abstract BACKGROUND: Legionella spp. are the etiological agents of Legionnaires’ disease, often severe pneumonia. After the first severe outbreak of Legionella spp., it was found widely dispersed in natural water sources and humid environments and has become a concern for these sources’ water quality and safety. The fecal indicators used for water quality assessment do not predict the presence of these pathogens; thus, in the absence of targeted analysis, the risk is unobserved until the emergence of infections. There is no study on the presence of Legionella in unattended water bodies in Bangladesh, such as swimming pools, air-conditioned cooling water, and stagnant circulatory water systems. METHODS: A total of 42 water samples were collected from 12 different sites in Dhaka, Bangladesh. Acid, heat, and chlorine treatment were applied to reduce the load of non-Legionellae in water samples. Chlorine treatment was used to kill unwanted organisms in water samples. After successful pretreatment, samples were cultured on buffered charcoal yeast extract agar (BCYE) media. Optimum pH, concentrations of chlorine, and temperature were set up by extensive trial and error culturing of Legionella on BCYE media to minimize other bacterial growth and maximize Legionella growth. Isolated colonies were confirmed primarily by morphological characteristics on BCYE media. Isolates were then confirmed by polymerase chain reaction and gel electrophoresis techniques. We detected the presence of 16S rDNA for Legionella spp. and the dnaJ gene for Legionella pneumophila species identification. Antibiotic sensitivity tests (minimum inhibitory concentration) were also conducted to see if it was alarming for our community’s health. RESULTS: Most of the Legionella spp. could grow at various temperatures, such as 45°C, 50°C, and 55°C, and they could also survive at the normal levels of chlorination, such as 0.25 mg/L and 0.5 mg/L. We have found that, out of 12 different sites, 4 out of 5 (80%) isolates from cooling tower water, 1 out of 4 (25%) from the swimming pool, and 1 out of 3 (33%) household stagnant water are contaminated with Legionella. However, 3 out of 5 isolates found are L. pneumophila from cooling water sites. Furthermore, strains of Legionella spp. were resistant to many antibiotics, such as ciprofloxacin, azithromycin, and tetracycline. CONCLUSIONS: Serious and fatal Legionella spp. (L. pneumophila) infections may be transmitted because of the widespread presence of these water sources and the large number of users in the community. This threat is worsened by the survival of Legionella under various commonly used antibiotic conditions and further exacerbated by their antibiotic resistance. Health-care professionals may face great challenges due to the lack of studies about its prevalence and treatment procedures.

Chlorine levels and a Legionella outbreak

Background: Legionella, first identified in the 1970s, is increasingly recognized as an opportunistic pathogen in healthcare facilities.1 The National University Hospital (NUH) is a large quaternary level academic hospital with 1,200 beds located in equatorial Singapore. Its first building, completed in 1985, still serves patients today. In 2022, the infection prevention team (IPT) was informed of two cases of nosocomial legionella, which sparked the start of an extensive investigation consisting of water quality testing of multiple sources, case finding, and formation of a water management committee. Methods: 250mL water samples were collected and cultured by an external vendor using direct membrane filtration followed by plating on selective agar according to ISO 11731 standards. Bacterial colonies were then identified, quantified and speciated. At the same time, NUH’s facility management measured chlorine levels using a portable colorimeter. Results: In total, we cultured 34 samples taken from sinks, shower heads, potable water dispensers. 91.2% of samples were positive for legionella. Of the 91.2%, 35.3% of sites grew Legionella pneumophila serogroup 1 while 79.4% of sites grew Legionella pneumophila serogroup 2-15. We attributed our high rates of legionella positivity to an aging plumbing system and Singapore’s high humidity and temperatures. In addition, the maximal temperature of our hot water is only 48-50 °C. Although chlorine levels were generally low, they were still within the local recommendation of less than 2ppm (Singapore does not have guidance on minimum chlorine levels). We found no statistically significant correlation between the number of legionella colony forming units (CFUs) and chlorine levels (ranging between 0.02 to 0.14ppm). This supports the United States Environmental Protection Agency’s recommendation, as well as the findings from in vitro and in vivo studies, for a minimal chlorine of 0.2 PPM at the taps for acute care hospitals.2,3However, these levels may be inadequate in the presence of acanthamoeba or a high biofilm load within water systems.4,5 Conclusion: Hospital water management programs should require a minimal level of chlorine at hospital taps and at levels above those recommended by public water systems, in order to control legionella growth. In addition, the formation of a hospital water management committee is essential to improve hospital water quality and put mitigation measures in place.

EOC 75 - Routine Maintenance Treatment of Hospital Water Systems with Monochloramine Effectively Controls Legionella Growth

EOC 75 - Routine Maintenance Treatment of Hospital Water Systems with Monochloramine Effectively Controls Legionella Growth

Efficacy of chlorine-based disinfectants to control Legionella within premise plumbing systems

Legionella is an opportunistic waterborne pathogen that causes Legionnaires’ disease. It poses a significant public health risk, especially to vulnerable populations in health care facilities. It is ubiquitous in manufactured water systems and is transmitted via inhalation or aspiration of aerosols/water droplets generated from water fixtures (e.g., showers and hand basins). As such, the effective management of premise plumbing systems (building water systems) in health care facilities is essential for reducing the risk of Legionnaires’ disease. Chemical disinfection is a commonly used control method and chlorine-based disinfectants, including chlorine, chloramine, and chlorine dioxide, have been used for over a century. However, the effectiveness of these disinfectants in premise plumbing systems is affected by various interconnected factors that can make it challenging to maintain effective disinfection. This systematic literature review identifies all studies that have examined the factors impacting the efficacy and decay of chlorine-based disinfectant within premise plumbing systems. A total of 117 field and laboratory-based studies were identified and included in this review. A total of 20 studies directly compared the effectiveness of the different chlorine-based disinfectants. The findings from these studies ranked the typical effectiveness as follows: chloramine > chlorine dioxide > chlorine. A total of 26 factors were identified across 117 studies as influencing the efficacy and decay of disinfectants in premise plumbing systems. These factors were sorted into categories of operational factors that are changed by the operation of water devices and fixtures (such as stagnation, temperature, water velocity), evolving factors which are changed in-directly (such as disinfectant concentration, Legionella disinfectant resistance, Legionella growth, season, biofilm and microbe, protozoa, nitrification, total organic carbon(TOC), pH, dissolved oxygen(DO), hardness, ammonia, and sediment and pipe deposit) and stable factors that are not often changed(such as disinfectant type, pipe material, pipe size, pipe age, water recirculating, softener, corrosion inhibitor, automatic sensor tap, building floor, and construction activity). A factor-effect map of each of these factors and whether they have a positive or negative association with disinfection efficacy against Legionella in premise plumbing systems is presented. It was also found that evaluating the effectiveness of chlorine disinfection as a water risk management strategy is further complicated by varying disinfection resistance of Legionella species and the form of Legionella (culturable/viable but non culturable, free living/biofilm associated, intracellular replication within amoeba hosts). Future research is needed that utilises sensors and other approaches to measure these key factors (such as pH, temperature, stagnation, water age and disinfection residual) in real time throughout premise plumbing systems. This information will support the development of improved models to predict disinfection within premise plumbing systems. The findings from this study will inform the use of chlorine-based disinfection within premise plumbing systems to reduce the risk of Legionnaires disease.

An outbreak of Legionnaires' disease linked to a municipal and industrial wastewater treatment plant, The Netherlands, September-October 2022.

Wastewater treatment plants (WWTPs) are increasingly identified as Legionnaires' disease (LD) sources. An outbreak investigation was initiated following five LD cases reported in September 2022 in Houten, the Netherlands. Case identification was based on the European LD case definition, with symptom onset from 1 September 2022, residence in or within 5 km of Houten, or visit to Houten within the incubation period, without other likely sources. We sampled potential sources and genotyped environmental and clinical isolates. We identified 15 LD cases with onset between 13 September and 23 October 2022. A spatial source identification and wind direction model suggested an industrial (iWWTP) and a municipal WWTP (mWWTP) as potential sources, with the first discharging water into the latter. Both tested positive for Legionella pneumophila serogroups 1 and 6 with multiple sequence types (ST). We detected L. pneumophila sg1 ST42 in the mWWTP, matching with one of three available clinical isolates. Following control measures at the WWTPs, no further cases were observed. This outbreak underlines that municipal and industrial WWTPs can play an important role in community LD cases and outbreaks, especially those with favourable conditions for Legionella growth and dissemination, or even non-favourable conditions for growth but with the influx of contaminated water.

Prevention of legionella infections from toilet flushing cisterns

INTRODUCTIONImmunocompromised patients are at an increased risk of severe Legionella infections. We present the results of an outbreak investigation initiated following a fatal case of hospital-acquired legionellosis linked to contaminated water from a toilet-flushing cistern. Additionally, we provide experimental data on the growth of Legionella spp. in flushing cisterns and propose a straightforward protocol for prevention. METHODSWe monitored the growth of Legionella spp. in the building's hot and cold-water systems using quantitative bacterial culture on selective agar. Molecular typing of L. pneumophila isolates from the infected patient and the water system was conducted through core-genome multilocus sequence typing (cgMLST). RESULTSLegionella contamination in the hospital building’s cold-water system was significantly higher than in the hot water system and significantly higher in toilet flushing cistern’s water compared to cold water from bathroom sinks and showers. Isolates from the patient and from the flushing cistern of the patient’s bathroom were identical by cgMLST. In an experimental setting, daily toilet flushing for a period of 21 days resulted in a 67 percent reduction in the growth of Legionella spp. in the water of toilet flushing cisterns. Moreover, a one-time disinfection of cisterns with peracetic acid, followed by daily flushing, decreased Legionella growth to less than 1% over a period of at least 7 weeks in these setting. CONCLUSIONSOne-time disinfection of highly contaminated cisterns with peracetic acid and daily toilet flushing as short-term measure can significantly reduce Legionella contamination in flushing cisterns. These measures may aid in preventing Legionella infection among immunocompromised patients.

Ethambutol inhibited the growth of acid-fast bacteria and enhanced the detection of Legionella in environmental water samples.

The growth of acid-fast bacteria often hinders the detection of Legionella in water samples on agar plates by the plate culture method. We studied whether anti-tubercular agents inhibit acid-fast bacteria growth on agar plates. First, the antimicrobial activities of isoniazid, ethionamide, and ethambutol were evaluated against Mycobacterium and Legionella. We found that ethambutol at ≥ 100 μg/mL completely inhibited Mycobacterium growth, but ethambutol at 1,000 μg/mL did not inhibit Legionella growth. Next, the effect of ethambutol dissolved in acid buffer was examined. Cell suspensions of L. pneumophila and Mycobacterium spp. were mixed, and ethambutol-acid buffer was added. After 5 min, mixtures were inoculated on GVPC agar plates and incubated at 36℃ for 6 d. We found that ethambutol inhibited Mycobacterium growth on agar plates, but the Legionella colonies recovered. The effect of ethambutol was also significant in the evaluation using bathwaters. Comparing 1,302 bathwaters, the addition of ethambutol reduced the detection rate of acid-fast bacteria from 30.6% to 0% and increased the detection rate of Legionella from 7.1% to 7.5%. Ethambutol, which selectively inhibited acid-fast bacteria growth, enhanced the detection of Legionella on agar plates and will contribute to improving the accuracy of Legionella testing by the plate culture method.

Effects of the COVID-19 Pandemic on Legionella Water Management Program Performance across a United States Lodging Organization.

Legionella, the bacterium that causes Legionnaires' disease, can grow and spread in building water systems and devices. The COVID-19 pandemic impacted building water systems through reductions in water usage. Legionella growth risk factors can be mitigated through control measures, such as flushing, to address stagnation, as part of a water management program (WMP). A national lodging organization (NLO) provided WMP data, including Legionella environmental testing results for periods before and during the pandemic. The statistical analysis revealed an increased risk of water samples testing positive for Legionella during the pandemic, with the greatest increase in risk observed at the building's cold-water entry test point. Sample positivity did not vary by season, highlighting the importance of year-round Legionella control activities. The NLO's flushing requirements may have prevented an increased risk of Legionella growth during the pandemic. However, additional control measures may be needed for some facilities that experience Legionella detections. This analysis provides needed evidence for the use of flushing to mitigate the impacts of building water stagnation, as well as the value of routine Legionella testing for WMP validation. Furthermore, this report reinforces the idea that WMPs remain the optimal tool to reduce the risk of Legionella growth and spread in building water systems.

Prevalence of Legionella in a Public Building Water Plumbing System During COVID-19 Lockdown.

Although water stagnation is widely accepted as an essential factor supporting Legionella growth in plumbing systems and "water flashing" has become a common action for water quality control, additional monitoring data in practical spaces are still needed to back up this recommendation. The lockdown of public buildings during the COVID-19 pandemic provided an ideal time window to collect such data on a large scale. This study investigated how the long-term lockdown of a public building and the subsequent water stagnation impact water quality and the population of Legionella in water. From June 2020 to May 2021, 192 water samples were collected from a public building during the lockdown and reopening due to the COVID-19 pandemic. Each water sample was assessed for common physicochemical characteristics. Concentrations of Legionella and three species of free-living amoeba (FLA) (Acanthamoeba spp., Naegleria fowleri, and Hartmannella vermiformis) were monitored by qPCR. The data suggest that long-term stagnation promotes the population of Legionella spp., Acanthamoeba spp., and N. fowleri. Notable associations were observed between Legionella and FLA. These relationships were impacted by stagnation. These results provide important evidence that can inform future water quality management actions to minimize the risk of Legionella outbreaks by avoiding the occurrence of water stagnation.

Legionella detection in wastewater treatment plants with increased risk for Legionella growth and emission.

Legionnaires' disease (LD) is a severe pneumonia mainly caused by the bacterium Legionella pneumophila. Although many environmental sources of LD have been described, the sources of the majority of non-outbreak LD cases have not been identified. In several outbreaks in the Netherlands, wastewater treatment plants (WWTPs) were identified as the most likely source of infection. In this study, four criteria for Legionella growth and emission to air and surface waters were selected based on the literature and a risk matrix was drafted. An inventory was made of all WWTPs and their characteristics in the Netherlands. The risk matrix was applied to identify WWTPs at risk for Legionella growth and emission. Wastewater was collected at WWTPs with moderate to high risk for Legionella growth and emission. In 18% of the sampled WWTPs, Legionella spp. was detected using culture methods. The presented risk matrix can be used to assess the risks of Legionella growth and emission for WWTPs and support surveillance by prioritizing WWTPs. When Legionella is detected in the wastewater, it is recommended to take action to prevent emission to air or discharge on surface waters and, if possible, reduce the Legionella concentration.

A Study on The Presence of Legionella pneumophila in Hospital Water Samples from Eastern Turkey

Objective: Legionnaires' disease is a fatal form of pneumonia brought on by an infection mostly caused by the 60 different species of Legionella pneumophila. Legionnaires' illness is caused by Legionella spp.-contaminated water systems. In this work, we sought to analyze Legionella species, serogroups (SG), and contamination in the water sources of hospitals in five regions in eastern Turkey.
 Methods: Between January 2017 and December 2018, a total of 1008 samples were examined, including 2 cooling towers, 62 hot water tanks, 104 cold water tanks, and 840 faucet shower heads. Samples were collected by the standard culture method L. pneumophila SG 1, it was analyzed for L. pneumophila SG 2-16 and Legionella spp. The samples were inoculated into BCYE and GVPC medium, and the colonies were assessed using a latex agglutination test, followed by species- and serotype-level identifications.
 Results: In our study, a total of 1008 water samples were examined, of which 35.31% (356) belonged to 2017, while 64.68% (652) belonged to 2018. 83.33% of the water samples were taken from faucets and shower heads, 10.32% from the cold water tank, 6.15% from the hot water tank, and 0.2% from the cooling tower, and the highest positivity rate was observed in the hot water tank with 12.60%. 7.04% (71) of the samples were positive, and 16.9% (12) of the positive samples were L. pneumophila SG 1, 77.46% (55) L. pneumophila SG 2-14 was detected, while 5.63% (4) were nonpneumophila (Legionella spp) it has been determined as.
 Conclusions: Legionella disease remains a significant public health threat. The water tanks of hospitals and hotels should be investigated more thoroughly, the necessary disinfection procedures should be carried out frequently. All hospitals should have water management policies, and towns and large buildings should establish comprehensive water system management programs that decrease Legionella growth and transmission. To enhance prevention measures and clinical diagnosis, we also need quicker ways of detecting Legionella in water systems and clinical samples.

Identification, prevention, and treatment of Legionella in bath facility water systems in South Korea

Legionella bacteria infect people via aerosol transmission. These pathogens can meaningfully affect people with weak immune systems and the older adult population. Legionella proliferate in water systems at temperatures between 25 and 45 °C, the optimum range for bath facilities. Here, we discuss how and where water systems can be contaminated by Legionella in bath facility water systems in South Korea. An epidemiological investigation of Legionella detection data from the Korea Disease Control and Prevention Agency was conducted to understand the tendencies of general outbreaks of water system types in building groups. Onsite investigations were then conducted to identify the causes of contamination in water systems in actual Legionella detection cases. According to annual Legionella detection data, the highest rate of Legionella was detected in hot bathtub water. Onsite investigations revealed that sand filter circulation systems for bathtubs are susceptible to Legionella growth. Overall, this study examined the mechanisms of buidling water systems from a building engineering perspective in order to provide valuable information for future studies and strategies to control Legionella growth in bath facility water systems.

Impact of prolonged hotel closures during the COVID-19 pandemic on Legionella infection risks.

In general, it is accepted that water stagnation and lack or poor maintenance in buildings are risk factors for Legionella growth. Then, in theory, the prolonged hotel closures due to the COVID-19 pandemic may have increased the risk of Legionella infections. However, there are very few field studies comparing the level of Legionella colonization in buildings before the pandemic and the new situation created after the lockdown. The objective of this study was to analyze these differences in a group of hotels that experienced prolonged closures in 2020 due to the COVID-19 pandemic. We have studied the Legionella spp. results, analyzed by standard culture, from the domestic water distribution systems of 73 hotels that experienced closures (from 1 to >4 months) during 2020, immediately after the reopening. The results were compared with those obtained in similar samplings of 2019. For the comparative analysis, we divided the hotels in two groups: Group A that have suffered closures for ≤3 months and Group B that remained closed for more than 3 months, both in relation to the opening period of 2019. In the Group B (36 sites), the frequency of positive samples in the hot water system increased from 6.7% in 2019 to 14.0% in 2020 (p < 0.05). In the Group A (37 sites), no significant differences were observed. No statistically significant differences were observed in terms of positive sites (defined as hotels with at least 1 positive sample), Legionella spp. concentrations and prevalence of Legionella pneumophila sg1 between the samplings of the two periods studied. The results suggest that hotels that suffered the longest prolonged closures (> 3 months) could have carried a higher risk of exposure to Legionella in the domestic hot water system. These findings highlight the importance of adequate preopening cleaning and disinfection procedures for hotel water systems, and the convenience of considering the most effective disinfection methods especially for hot water systems and after prolonged closure periods.

Legionella pneumonia as a rising public health threat in Argentina: Is it the time to worry?

Legionella pneumonia as a rising public health threat in Argentina: Is it the time to worry?

Legionella and the Role of Dissolved Oxygen in Its Growth and Inhibition: A Review

This review discusses the relationship between dissolved oxygen and Legionella growth. Growth of Legionella in building water systems is considered to pose a health risk and controlling it could benefit public health by reducing the number of healthcare and community acquired Legionnaires’ disease cases. Conditions known to encourage Legionella growth include low disinfectant concentrations, warm temperature, and water stagnation. Legionella is an obligate aerobe meaning its cellular respiration is inhibited under anaerobic conditions. Despite evidence from earlier published studies the importance of dissolved oxygen for the survival and growth of Legionella has received little attention from researchers and public health authorities. Modern measurement devices can reliably determine if dissolved oxygen concentrations in potable water and other building water systems are at levels capable of supporting Legionella growth or inhibiting its amplification. Removing dissolved oxygen from water can be achieved using gas transfer membrane contactors. Water with low dissolved oxygen levels interferes with Legionella’s cellular respiration by oxygen starvation, whereas disinfectants achieve the same effect by interfering with oxygen transport across the cell membrane. Ultimately, the same effect on Legionella growth may be achieved by reducing dissolved oxygen as treatment with oxidants, while avoiding the drawbacks of corrosion and disinfectant byproducts.

Factors That Affect Legionella Positivity in Healthcare Building Water Systems from a Large, National Environmental Surveillance Initiative.

Legionella growth in healthcare building water systems can result in legionellosis, making water management programs (WMPs) important for patient safety. However, knowledge is limited on Legionella prevalence in healthcare buildings. A dataset of quarterly water testing in Veterans Health Administration (VHA) healthcare buildings was used to examine national environmental Legionella prevalence from 2015 to 2018. Bayesian hierarchical logistic regression modeling assessed factors influencing Legionella positivity. The master dataset included 201,146 water samples from 814 buildings at 168 VHA campuses. Overall Legionella positivity over the 4 years decreased from 7.2 to 5.1%, with the odds of a Legionella-positive sample being 0.94 (0.90-0.97) times the odds of a positive sample in the previous quarter for the 16 quarters of the 4 year period. Positivity varied considerably more at the medical center campus level compared to regional levels or to the building level where controls are typically applied. We found higher odds of Legionella detection in older buildings (OR 0.92 [0.86-0.98] for each more recent decade of construction), in taller buildings (OR 1.20 [1.13-1.27] for each additional floor), in hot water samples (O.R. 1.21 [1.16-1.27]), and in samples with lower residual biocide concentrations. This comprehensive healthcare building review showed reduced Legionella detection in the VHA healthcare system over time. Insights into factors associated with Legionella positivity provide information for healthcare systems implementing WMPs and for organizations setting standards and regulations.

Phosphate drinking water softeners promote Legionella growth.

Phosphate-based drinking water softeners are commonly used to prevent scale formation in drinking water distribution infrastructure. The main reason for drinking water softening is primarily economic (protection of pipes and extension of equipment life), while the health aspect of such treatment is usually neglected. The aim of this work is to investigate the effects of phosphate-based drinking water softeners on growth stimulation of Legionella pneumophila. Bacterial growth was observed at two different phosphate concentrations. On average, an increase in growth of 1.19-1.28 log CFU/mL was observed in selected samples with added phosphates compared with the control. The results of the in vitro experiment confirmed that the added phosphates stimulate the growth of L. pneumophila; growth stimulation could therefore be expected in drinking water distribution systems (DWDS) when phosphates are used as well. The availability of phosphorus in DWDS may be a crucial limiting factor for biofouling control. Consequently, phosphate-based chemicals for drinking water should be avoided or used with prudence, especially in drinking water with high concentrations of other nutrients.