Temperature diagnostic to identify high risk areas and optimize Legionella pneumophila surveillance in hot water distribution systems

Two-year evaluation of Legionella in an aging residential building: Assessment of multiple potable water remediation approaches

Legionella is an opportunistic waterborne pathogen that is difficult to eradicate in colonized drinking water pipes. Legionella control is further challenged by aging water infrastructure and lack of evidence-based guidance for building treatment. This study assessed multiple premise water remediation approaches designed to reduce Legionella pneumophila within a residential building located in an aging, urban drinking water system over a two-year period. Samples (n = 745) were collected from hot and cold-water lines and quantified via most probable number culture. Building-level treatment approaches included three single heat shocks, three single chemical shocks, and continuous low-level chemical disinfection in the potable water system. The building was highly colonized with L. pneumophila with 71 % L. pneumophila positivity. Single heat shocks had a statistically significant L. pneumophila reduction one day post treatment but no significant L. pneumophila reduction at one week, two weeks, and four weeks post treatment. The first two chemical shocks resulted in statistically significant L. pneumophila reduction at two days and four weeks post treatment, but there was a significant L. pneumophila increase at four weeks following the third chemical shock. Continuous low-level chemical disinfection resulted in statistically significant L. pneumophila reduction at ten weeks post treatment implementation. This demonstrates that in a building highly colonized with L. pneumophila, sustained remediation is best achieved using continuous low-level chemical treatment.

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 [...].

Two-Year Evaluation of Legionella in an Aging Residential Building: Assessment of Multiple Potable Water Remediation Approaches

Legionella is an opportunistic waterborne pathogen that is difficult to eradicate in colonized drinking water pipes. Legionella control is further challenged by aging water infrastructure and lack of evidence-based guidance for building treatment. This study assessed multiple premise water remediation approaches designed to reduce Legionella pneumophila (Lp) within a residential building located in an aging, urban drinking water system over a two-year period. Samples (n=745) were collected from hot and cold-water lines and quantified via most probable number culture. Building-level treatment approaches included three single heat shocks (HS), three single chemical shocks (CS), and continuous low-level chemical disinfection (CCD) in the potable water system. The building was highly colonized with Lp with 71% Lp positivity. Single HS had a statistically significant Lp reduction one day post treatment but no significant Lp reduction one, two, and four weeks post treatment. The first two CS resulted in statistically significant Lp reduction at two days and four weeks post treatment, but there was a significant Lp increase at four weeks following the third CS. CCD resulted in statistically significant Lp reduction ten weeks post treatment implementation. This demonstrates that in a building highly colonized with Lp, sustained remediation is best achieved using CCD.

A Critical Review on the Factors that Influence Opportunistic Premise Plumbing Pathogens: From Building Entry to Fixtures in Residences

Residential buildings provide unique conditions for opportunistic premise plumbing pathogen (OPPP) exposure via aerosolized water droplets produced by showerheads, faucets, and tubs. The objective of this review was to critically evaluate the existing literature that assessed the impact of potentially enhancing conditions to OPPP occurrence associated with residential plumbing and to point out knowledge gaps. Comprehensive studies on the topic were found to be lacking. Major knowledge gaps identified include the assessment of OPPP growth in the residential plumbing, from building entry to fixtures, and evaluation of the extent of the impact of typical residential plumbing design (e.g., trunk and branch and manifold), components (e.g., valves and fixtures), water heater types and temperature setting of operation, and common pipe materials (copper, PEX, and PVC/CPVC). In addition, impacts of the current plumbing code requirements on OPPP responses have not been assessed by any study and a lack of guidelines for OPPP risk management in residences was identified. Finally, the research required to expand knowledge on OPPP amplification in residences was discussed.

Persistent contamination of a hospital hot water network by Legionellapneumophila

OBJECTIVES

We assessed the contamination with Legionella pneumophila (Lp) of the hot water network (HWN) of a hospital, mapped the risk of contamination, and evaluated the relatedness of isolates. We further validated phenotypically the biological features that could account for the contamination of the network.

METHODS

We collected 360 water samples from October 2017 to September 2018 in 36 sampling points of a HWN of a building from a hospital in France. Lp were quantified and identified with culture-based methods and serotyping. Lp concentrations were correlated with water temperature, date and location of isolation. Lp isolates were genotyped by pulsed-field gel electrophoresis and compared to a collection of isolates retrieved in the same HWN two years later, or in other HWN from the same hospital.

RESULTS

207/360 (57.5%) samples were positive with Lp. In the hot water production system, Lp concentration was negatively associated with water temperature. In the distribution system, the risk of recovering Lp decreased when temperature was >55 °C (p < 10^-3), the proportion of samples with Lp increased with distance from the production network (p < 10^-3), and the risk of finding high loads of Lp increased 7.96 times in summer (p = 0.001). All Lp isolates (n = 135) were of serotype 3, and 134 (99.3%) shared the same pulsotype which is found two years later (Lp G). In vitro competition experiments showed that a 3-day culture of Lp G on agar inhibited the growth of a different pulsotype of Lp (Lp O) contaminating another HWN of the same hospital (p = 0.050). We also found that only Lp G survived to a 24h-incubation in water at 55 °C (p = 0.014).

CONCLUSION

We report here a persistent contamination with Lp of a hospital HWN. Lp concentrations were correlated with water temperature, season, and distance from the production system. Such persistent contamination could be due to biotic parameters such as intra-Legionella inhibition and tolerance to high temperature, but also to the non-optimal configuration of the HWN that prevented the maintenance of high temperature and optimal water circulation.

Surveillance of Legionella pneumophila: Detection in Public Swimming Pool Environment

The bacterium Legionella pneumophila is a ubiquitous microorganism naturally present in water environments. The actual presence of this opportunistic premise plumbing pathogen in recreational swimming pools and hot tubs in the northwestern part of Croatia has not been investigated. This study aimed to analyze the presence of the opportunistic pathogen L. pneumophila in public swimming pool water in Primorje-Gorski Kotar County (N = 4587) over a four-year period (2018-2021). Additionally, the second aim was to investigate the connection between the presence of L. pneumophila and pool water physicochemical parameters using mathematical predictive models. The presence of L. pneumophila was detected in six pool samples. Five positive samples were found in the water of indoor hot tubs filled with fresh water, and one positive sample in an outdoor recreational saltwater pool. A predictive mathematical model showed the simultaneous influence of chemical parameters dominated by the temperature in saltwater and freshwater pools, as well as the significant influence of free residual chlorine and trihalomethanes. Our results pointed out that keeping all physicochemical parameters in perfect harmony is necessary to reach the best disinfection procedure and to avoid the optimum conditions for L. pneumophila occurrence.

Variable Legionella Response to Building Occupancy Patterns and Precautionary Flushing

When stay-at-home orders were issued to slow the spread of COVID-19, building occupancy (and water demand) was drastically decreased in many buildings. There was concern that widespread low water demand may cause unprecedented Legionella occurrence and Legionnaires’ disease incidence. In lieu of evidenced-based guidance, many people flushed their water systems as a preventative measure, using highly variable practices. Here, we present field-scale research from a building before, during, and after periods of low occupancy, and controlled stagnation experiments. We document no change, a > 4-log increase, and a > 1.5-log decrease of L. pneumophila during 3- to 7-week periods of low water demand. L. pneumophila increased by > 1-log after precautionary flushing prior to reoccupancy, which was repeated in controlled boiler flushing experiments. These results demonstrate that the impact of low water demand (colloquially called stagnation) is not as straight forward as is generally assumed, and that some flushing practices have potential unintended consequences. In particular, stagnation must be considered in context with other Legionella growth factors like temperature and flow profiles. Boiler flushing practices that dramatically increase the flow rate and rapidly deplete boiler temperature may mobilize Legionella present in biofilms and sediment.

Tenets of a holistic approach to drinking water-associated pathogen research, management, and communication

In recent years, drinking water-associated pathogens that can cause infections in immunocompromised or otherwise susceptible individuals (henceforth referred to as DWPI), sometimes referred to as opportunistic pathogens or opportunistic premise plumbing pathogens, have received considerable attention. DWPI research has largely been conducted by experts focusing on specific microorganisms or within silos of expertise. The resulting mitigation approaches optimized for a single microorganism may have unintended consequences and trade-offs for other DWPI or other interests (e.g., energy costs and conservation). For example, the ecological and epidemiological issues characteristic of Legionella pneumophila diverge from those relevant for Mycobacterium avium and other nontuberculous mycobacteria. Recent advances in understanding DWPI as part of a complex microbial ecosystem inhabiting drinking water systems continues to reveal additional challenges: namely, how can all microorganisms of concern be managed simultaneously? In order to protect public health, we must take a more holistic approach in all aspects of the field, including basic research, monitoring methods, risk-based mitigation techniques, and policy. A holistic approach will (i) target multiple microorganisms simultaneously, (ii) involve experts across several disciplines, and (iii) communicate results across disciplines and more broadly, proactively addressing source water-to-customer system management.

Practitioners’ Perspective on the Prevalent Water Quality Management Practices for Legionella Control in Large Buildings in the United States

Managing building water systems is complicated by the need to maintain hot water temperatures high enough to control the growth of Legionella spp. while minimizing the risk of scalding. This study assessed water quality management practices in large buildings in the United States. Surveys conducted with building water quality managers found that more than 85% of buildings have hot water temperatures that are consistent with scald risk mitigation guidelines (i.e., <122 °F/50 °C). However, nearly two thirds and three quarters of buildings do not comply with the common temperature guidance for opportunistic pathogen control, i.e., water heater setpoint > 140 °F (60 °C) and recirculation loop > 122 °F (50 °C), respectively; median values for both setpoint and recirculation loop temperatures are 10 °F (6 °C) or more below temperatures recommended for opportunistic pathogen control. These observations suggest that many buildings are prone to Legionella spp. risk. The study also found that 27% of buildings do not comply with guidelines for time to equilibrium hot water temperature, over 33% fail to monitor temperature in the recirculation loop, more than 70% fail to replace or disinfect showerheads, more than 40% lack a written management plan, and only a minority conduct any monitoring of residual disinfectant levels or microbiological quality. Given the rise in Legionellosis infections in recent years, coupled with highlighted water quality concerns because of prolonged water stagnation in plumbing, such as in buildings closed due to COVID-19, current management practices, which appear to be focused on scald risk, may need to be broadened to include greater attention to control of opportunistic pathogens. To accomplish this, there is a need for formal training and resources for facility managers.

Compromised Effectiveness of Thermal Inactivation of Legionella pneumophila in Water Heater Sediments and Water, and Influence of the Presence of Vermamoeba vermiformis

Intermittent reduction of temperature set-points and periodic shutdowns of water heaters have been proposed to reduce energy consumption in buildings. However, the consequences of such measures on the occurrence and proliferation of Legionella pneumophila (Lp) in hot water systems have not been documented. The impact of single and repeated heat shocks was investigated using an environmental strain of L. pneumophila and a reference strain of V. vermiformis. Heat shocks at temperatures ranging from 50 °C to 70 °C were applied for 1 h and 4 h in water and water heaters loose deposits (sludge). The regrowth potential of heat-treated culturable L. pneumophila in presence of V. vermiformis in water heaters sludges was evaluated. A 2.5-log loss of culturability of L. pneumophila was observed in simulated drinking water at 60 °C while a 4-log reduction was reached in water heaters loose deposits. Persistence of Lp after 4 h at 55 °C was shown and the presence of V. vermiformis in water heater’s loose deposits resulted in a drastic amplification (5-log). Results show that thermal inactivation by heat shock is only efficient at elevated temperatures (50 °C) in both water and loose deposits. The few remaining organisms can rapidly proliferate during storage at lower temperature in the presence of hosts.

The Tail-Specific Protease Is Important for Legionella pneumophila To Survive Thermal Stress in Water and inside Amoebae

Legionella pneumophila (Lp) is an inhabitant of natural and human-made water systems, where it replicates within amoebae and ciliates and survives within biofilms. When Lp-contaminated aerosols are breathed in, Lp can enter the lungs and may infect human alveolar macrophages, causing severe pneumonia known as Legionnaires' disease. Lp is often found in hot water distribution systems (HWDS), which are linked to nosocomial outbreaks. Heat treatment is used to disinfect HWDS and reduce the concentration of Lp However, Lp is often able to recolonize these water systems, indicating an efficient heat shock response. Tail-specific proteases (Tsp) are typically periplasmic proteases implicated in degrading aberrant proteins in the periplasm and important for surviving thermal stress. In Lp Philadelphia-1, Tsp is encoded by the lpg0499 gene. In this paper, we show that Tsp is important for surviving thermal stress in water and for optimal infection of amoeba when a shift in temperature occurs during intracellular growth. We also demonstrate that Tsp is expressed in the postexponential phase but repressed in the exponential phase and that the cis-encoded small regulatory RNA Lpr17 shows the opposite expression, suggesting that it represses translation of tsp In addition, our results show that tsp is regulated by CpxR, a major regulator in Lp, in an Lpr17-independent manner. Deletion of CpxR also reduced the ability of Lp to survive heat shock. In conclusion, our study shows that Tsp is likely an important factor for the survival and growth of Lp in water systems.IMPORTANCE Lp is a major cause of nosocomial and community-acquired pneumonia. Lp is found in water systems, including hot water distribution systems. Heat treatment is a method of disinfection often used to limit the presence of Lp in such systems; however, the benefit is usually short term, as Lp is able to quickly recolonize these systems. Presumably, Lp responds efficiently to thermal stress, but so far, not much is known about the genes involved. In this paper, we show that the Tsp and the two-component system CpxRA are required for resistance to thermal stress when Lp is free in water and when it is inside host cells. Our study identifies critical systems for the survival of Lp in its natural environment under thermal stress.

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.

Legionellosis Caused by Non-Legionella pneumophila Species, with a Focus on Legionella longbeachae

Although known as causes of community-acquired pneumonia and Pontiac fever, the global burden of infection caused by Legionella species other than Legionella pneumophila is under-recognised. Non-L. pneumophila legionellae have a worldwide distribution, although common testing strategies for legionellosis favour detection of L. pneumophila over other Legionella species, leading to an inherent diagnostic bias and under-detection of cases. When systematically tested for in Australia and New Zealand, L. longbeachae was shown to be a leading cause of community-acquired pneumonia. Exposure to potting soils and compost is a particular risk for infection from L. longbeachae, and L. longbeachae may be better adapted to soil and composting plant material than other Legionella species. It is possible that the high rate of L. longbeachae reported in Australia and New Zealand is related to the composition of commercial potting soils which, unlike European products, contain pine bark and sawdust. Genetic studies have demonstrated that the Legionella genomes are highly plastic, with areas of the chromosome showing high levels of recombination as well as horizontal gene transfer both within and between species via plasmids. This, combined with various secretion systems and extensive effector repertoires that enable the bacterium to hijack host cell functions and resources, is instrumental in shaping its pathogenesis, survival and growth. Prevention of legionellosis is hampered by surveillance systems that are compromised by ascertainment bias, which limits commitment to an effective public health response. Current prevention strategies in Australia and New Zealand are directed at individual gardeners who use potting soils and compost. This consists of advice to avoid aerosols generated by the use of potting soils and use masks and gloves, but there is little evidence that this is effective. There is a need to better understand the epidemiology of L. longbeachae and other Legionella species in order to develop effective treatment and preventative strategies globally.

Evaluation of Recommended Water Sample Collection Methods and the Impact of Holding Time on Legionella Recovery and Variability from Healthcare Building Water Systems

Water safety and management programs (WSMP) utilize field measurements to evaluate control limits and monitor water quality parameters including Legionella presence. This monitoring is important to verify that the plan is being implemented properly. However, once it has been determined when and how to sample for Legionella, it is important to choose appropriate collection and processing methods. We sought to compare processing immediate and flushed samples, filtration of different volumes collected, and sample hold times. Hot water samples were collected immediately and after a 2-min flush. These samples were plated directly and after filtration of either 100 mL, 200 mL, or 1 L. Additionally, unflushed samples were collected and processed immediately and after 1, 24, and 48 h of hold time. We found that flushed samples had significant reductions in Legionella counts compared to immediate samples. Processing 100 mL of that immediate sample both directly and after filter concentration yielded the highest concentration and percent sample positivity, respectively. We also show that there was no difference in culture values from time 0 compared to hold times of 1 h and 24 h. At 48 h, there were slightly fewer Legionella recovered than at time 0. However, Legionella counts were so variable based on sampling location and date that this hold time effect was minimal. The interpretation of Legionella culture results depends on the sample collection and processing methods used, as these can have a huge impact on the success of sampling and the validation of control measures.

Implementation of Legionella Prevention Policy in Health Care Facilities: The United States Veterans Health Administration Experience

CONTEXT

The Veterans Health Administration requires implementation of Legionella prevention policy in potable water systems at Department of Veterans Affairs (VA) medical facilities across the United States and territories.

PROGRAM

The Veterans Health Administration Central Office program offices with expertise in engineering and clinical aspects of Legionella prevention policy have provided joint, structured on-site assistance to VA medical facilities for consultation on policy implementation. Site visits included review of facility documentation and data, discussions with staff, touring of buildings, and development of recommendations.

IMPLEMENTATION

Information obtained from on-site consultative assistance provided to VA medical facilities from December 2012 through January 2018 was reviewed to identify engineering and clinical challenges and lessons from implementation of Legionella prevention policy in VA health care buildings. Fifteen consultative site visits were conducted during this period regarding implementation of Legionella prevention and validation of effectiveness.

EVALUATION

It was found that implementation of Legionella prevention policy in potable water systems was complex and practices varied for each building. Common implementation challenges included capability of applying engineering controls, water stagnation, and assessment of health care association of Legionella cases. Process challenges included routine verification of actions, methods for assessing environmental validation data, and documentation of requirements. It was found that consistent and data-driven implementation of policy is crucial for an effective program.

DISCUSSION

Guidance and standards documents in the community for Legionella prevention in building water systems are often general in nature, but implementation requires specific decisions and routine assessments and modifications to optimize outcomes. This real-world review of challenges and lessons from a large health care system with a detailed primary Legionella prevention policy informs future development of guidance and policy, both within and external to VA, and can provide insight to other health care facilities planning to implement practices for water safety.

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.

Considerations for large building water quality after extended stagnation

The unprecedented number of building closures related to the coronavirus disease (COVID-19) pandemic is concerning because water stagnation will occur in many buildings that do not have water management plans in place. Stagnant water can have chemical and microbiological contaminants that pose potential health risks to occupants. Health officials, building owners, utilities, and other entities are rapidly developing guidance to address this issue, but the scope, applicability, and details included in the guidance vary widely. To provide a primer of large building water system preventative and remedial strategies, peer-reviewed, government, industry, and nonprofit literature relevant to water stagnation and decontamination practices for plumbing was synthesized. Preventative practices to help avoid the need for recommissioning (e.g., routine flushing) and specific actions, challenges, and limitations associated with recommissioning were identified and characterized. Considerations for worker and occupant safety were also indicated. The intended audience of this work includes organizations developing guidance.

Considerations for Large Building Water Quality after Extended Stagnation

The unprecedented number of building closures related to the coronavirus disease (COVID‐19) pandemic is concerning because water stagnation will occur in many buildings that do not have water management plans in place. Stagnant water can have chemical and microbiological contaminants that pose potential health risks to occupants. Health officials, building owners, utilities, and other entities are rapidly developing guidance to address this issue, but the scope, applicability, and details included in the guidance vary widely. To provide a primer of large building water system preventative and remedial strategies, peer‐reviewed, government, industry, and nonprofit literature relevant to water stagnation and decontamination practices for plumbing was synthesized. Preventative practices to help avoid the need for recommissioning (e.g., routine flushing) and specific actions, challenges, and limitations associated with recommissioning were identified and characterized. Considerations for worker and occupant safety were also indicated. The intended audience of this work includes organizations developing guidance.

Impact of temperature on Legionella pneumophila, its protozoan host cells, and the microbial diversity of the biofilm community of a pilot cooling tower

Legionella pneumophila is a waterborne bacterium known for causing Legionnaires' Disease, a severe pneumonia. Cooling towers are a major source of outbreaks, since they provide ideal conditions for L. pneumophila growth and produce aerosols. In such systems, L. pneumophila typically grow inside protozoan hosts. Several abiotic factors such as water temperature, pipe material and disinfection regime affect the colonization of cooling towers by L. pneumophila. The local physical and biological factors promoting the growth of L. pneumophila in water systems and its spatial distribution are not well understood. Therefore, we built a lab-scale cooling tower to study the dynamics of L. pneumophila colonization in relationship to the resident microbiota and spatial distribution. The pilot was filled with water from an operating cooling tower harboring low levels of L. pneumophila. It was seeded with Vermamoeba vermiformis, a natural host of L. pneumophila, and then inoculated with L. pneumophila. After 92 days of operation, the pilot was disassembled, the water was collected, and biofilm was extracted from the pipes. The microbiome was studied using 16S rRNA and 18S rRNA genes amplicon sequencing. The communities of the water and of the biofilm were highly dissimilar. The relative abundance of Legionella in water samples reached up to 11% whereas abundance in the biofilm was extremely low (≤0.5%). In contrast, the host cells were mainly present in the biofilm. This suggests that L. pneumophila grows in host cells associated with biofilm and is then released back into the water following host cell lysis. In addition, water temperature shaped the bacterial and eukaryotic community of the biofilm, indicating that different parts of the systems may have different effects on Legionella growth.

Presence of Legionella spp. in cooling towers: the role of microbial diversity, Pseudomonas, and continuous chlorine application

Legionnaires' disease (LD) is a severe pneumonia caused by several species of the genus Legionella, most frequently by Legionella pneumophila. Cooling towers are the most common source for large community-associated outbreaks. Colonization, survival, and proliferation of L. pneumophila in cooling towers are necessary for outbreaks to occur. These steps are affected by the chemical and physical parameters of the cooling tower environment. We hypothesize that the bacterial community residing in the cooling tower could also affect the presence of L. pneumophila. A 16S rRNA gene targeted amplicon sequencing approach was used to study the bacterial community of cooling towers and its relationship with the Legionella spp. and L. pneumophila communities. The results indicated that the water source shaped the bacterial community of cooling towers. Several taxa were enriched and positively correlated with Legionella spp. and L. pneumophila. In contrast, Pseudomonas showed a strong negative correlation with Legionella spp. and several other genera. Most importantly, continuous chlorine application reduced microbial diversity and promoted the presence of Pseudomonas creating a non-permissive environment for Legionella spp. This suggests that disinfection strategies as well as the resident microbial population influences the ability of Legionella spp. to colonize cooling towers.

Managing Water Quality in Premise Plumbing: Subject Matter Experts’ Perspectives and a Systematic Review of Guidance Documents

Although many guidance documents have been developed to inform the design and operation of building water systems to ensure safe water quality, there is a lack of consensus on some topics. This study interviewed 22 subject matter experts (SMEs) to identify topics of concern for managing water quality in buildings and compared SME views with information available on these topics in 15 systematically screened important guidance documents. The study found 18 design and 11 operational topics as critical for managing water quality in buildings. No one guidance document addressed all these topics, suggesting that a compendium of available guidance is needed. SMEs most frequently recommended temperature and residual disinfectant measurements as good parameters for monitoring overall building water quality. Both SME and guidance document recommendations for temperature for controlling opportunistic pathogen growth were reasonably consistent with water heater setpoint >60 °C. However, hot water temperature recommendations varied between 50 and 55 °C for other locations (i.e., the water temperature at the tap or end of the return loop). On the contrary, recommendations for disinfectant residual levels (0.2–2.0 mg/L), flushing frequency (1–14 days), and allowable time for hot water to reach the tap (10–60 s) were not consistent. While this study was able to reconcile diverging views on some of the water quality topics, such as identifying common guidance for water heater set point to at least 60 °C, it also highlights lack of definitive guidance on other critical topics, such as residual level, flushing frequency, hot water time to tap, and the use of thermostatic mixing valves, indicating that these are significant knowledge gaps that need further investigation. The study concludes that there is a need for developing evidence-based guidance, particularly on the topics where expert opinions diverged.

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.

Overview and comparison of Legionella regulations worldwide

BACKGROUND

Legionnaires disease occurs worldwide. Many authorities have guidelines and regulations to prevent and control Legionella in water systems. These regulations are based on often very limited field and laboratory observations and measurements. They are, therefore, very different from country to country. This article aims to map the existing regulatory framework of worldwide Legionella control to assess the feasibility of regulatory unification.

METHODS

This article gives an overview of the different standards, guidelines, and recommendations as well as how various authorities and/or countries deal with Legionella infection. A 3-step process is followed to identify current regulations.

RESULTS

Although Legionella is a global concern with a common scientific base, the regulatory framework is different from country to country. The current guidelines and standards are not the best possible. Despite different regulatory frameworks, there is still broad unification of underlying principles. Common principles across regulations are avoiding and monitoring critical spots, avoiding water stagnation, and maintaining sufficiently high temperature (above 60°C, below 25°C). Differences between regulations are target group and dangerous Legionella concentration levels.

CONCLUSIONS

The comparative analysis of the framework is a good starting point for reaching future regulatory unification based on common ground.

Viability and infectivity of viable but nonculturable Legionella pneumophila strains induced at high temperatures

Thermal disinfection is commonly used to prevent the proliferation of culturable Legionella in engineered water systems (EWS). In response to such stress, culturable Legionella populations can switch into a viable but nonculturable (VBNC) state. The importance of such VBNC Legionella cells is currently hotly debated. Here, we investigated the stress response patterns and transitions of the bacteria to the VBNC state at 55 °C, 60 °C and 70 °C on two L. pneumophila strains for >80 days using a combination of cell-based viability indicators. Complete loss of culturability at 55 °C, 60 °C and 70 °C occurred after 3-8 h, 60 min and <2 min, respectively. In contrast, L. pneumophila strains required 9 days at 55 °C, 8 h at 60 °C and 20 min at 70 °C to achieve a 2 log reduction in cells with intact membranes and high esterase activity; a 4 log reduction was achieved only after 150, 8-15 and 1-4 days, respectively. In parallel, the presence of diagnostic outer-membrane epitopes (OMEs) and changes in the infectivity patterns of the two strains towards amoebae and THP-1 cells were assessed. OMEs were more persistent than viability indicators, showing their potential as targets for VBNC Legionella detection. L. pneumophila strains infected amoebae and THP-1 cells for at least 85 days at 55 °C and 60 °C and for up to 8 days at 70 °C. However, they did so with reduced efficiency, requiring prolonged co-incubation times with the hosts and higher Legionella cell numbers in comparison to culturable cells. Consequently, infection of amoebae by thermally induced VBNC L. pneumophila with lowered virulence can be expected in EWS. Although the gold standard method cannot detect VBNC Legionella, it provides important information about the most virulent bacterial subpopulations. Our results indicate that a prolonged thermal regime ≥60 °C at the central parts of warm water systems is not only effective against culturable L. pneumophila but in the long run even against VBNC cells.

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.

Role of hot water temperature and water system use on Legionella control in a tertiary hospital: An 8-year longitudinal study

Although measures to minimize Legionella colonization in sanitary hot water installations are well established, there is little evidence of their long-term effectiveness in hospital buildings. During an 8-year period, hot water in a large hospital building was sampled monthly in areas with suitable dimensioning and recirculation and in areas with dead legs and low-use taps. In the former areas, the percentage of Legionella-negative samples was 83.2% when the temperature was ≥55%, 64.9% when between 50.1 °C and 54.0 °C, and 51.6% when ≤50 °C (p for trend <0.001). In the highest temperature group, no samples with ≥10³ cfu/L were observed. In poorly designed areas, only 44.7% of samples were negative, and 28.9% presented ≥10³ cfu/L although reaching 55 °C. In these areas, multivariate analysis showed that if hot water supplies were not used daily, the risk of Legionella colonization was greater than two-fold (odds ratio: 2.84; 95% confidence interval: 1.26-6.41), and the risk of finding Legionella concentrations ≥10³ cfu/L was more than three-fold (odds ratio: 3.18; 95% confidence interval: 1.36-7.46), regardless the temperature. These findings indicate that the effectiveness of maintaining sanitary hot water at a minimum temperature of 55 °C is significantly better than that at 50 °C for the environmental control of Legionella but only in installations with suitable dimensioning and recirculation. In installations that do not meet these conditions, high temperatures alone result in insufficient control.

Shotgun Metagenomics Reveals Taxonomic and Functional Shifts in Hot Water Microbiome Due to Temperature Setting and Stagnation

Hot water premise plumbing has emerged as a critical nexus of energy, water, and public health. The composition of hot water microbiomes is of special interest given daily human exposure to resident flora, especially opportunistic pathogens (OPs), which rely on complex microbial ecological interactions for their proliferation. Here, we applied shotgun metagenomic sequencing to characterize taxonomic and functional shifts in microbiomes as a function of water heater temperature setting, stagnation in distal pipes, and associated shifts in water chemistry. A cross-section of samples from controlled, replicated, pilot-scale hot water plumbing rigs representing different temperature settings (39, 42, and 51°C), stagnation periods (8 h vs. 7 days), and time-points, were analyzed. Temperature setting exhibited an overarching impact on taxonomic and functional gene composition. Further, distinct taxa were selectively enriched by specific temperature settings (e.g., Legionella at 39°C vs. Deinococcus at 51°C), while relative abundances of genes encoding corresponding cellular functions were highly consistent with expectations based on the taxa driving these shifts. Stagnation in distal taps diminished taxonomic and functional differences induced by heating the cold influent water to hot water in recirculating line. In distal taps relative to recirculating hot water, reads annotated as being involved in metabolism and growth decreased, while annotations corresponding to stress response (e.g., virulence disease and defense, and specifically antibiotic resistance) increased. Reads corresponding to OPs were readily identified by metagenomic analysis, with L. pneumophila reads in particular correlating remarkably well with gene copy numbers measured by quantitative polymerase chain reaction. Positive correlations between L. pneumophila reads and those of known protozoan hosts were also identified. Elevated proportions of genes encoding metal resistance and hydrogen metabolism were noted, which was consistent with elevated corrosion-induced metal concentrations and hydrogen generation. This study provided new insights into real-world factors influencing taxonomic and functional compositions of hot water microbiomes. Here metagenomics is demonstrated as an effective tool for screening for potential presence, and even quantities, of pathogens, while also providing diagnostic capabilities for assessing functional responses of microbiomes to various operational conditions. These findings can aid in informing future monitoring and intentional control of hot water microbiomes.

Legionella pneumophila recurrently isolated in a Spanish hospital: Two years of antimicrobial resistance surveillance

OBJECTIVES

The aim of this study was to monitor the spread, persistence and antibiotic resistance patterns of Legionella spp. strains found in a hospital water distribution system. These environmental studies are intended to help detect the presence of antibiotic resistant strains before they infect patients.

METHODS

Antimicrobial surveillance tests were performed at 27 different sampling points of the water network of a large Spanish hospital over two years. Water samples were screened for Legionella according to ISO 11731:2007. Legionella spp. isolates were identified by serotyping and by mass spectrometry (MALDI-ToF). Epidemiological molecular typing was done by Pulse-Field Gel Electrophoresis (PFGE) and by Sequence-Based Typing (SBT). Antibiotic susceptibility tests were performed using disk diffusion and ETEST®.

RESULTS

Legionella spp. were recurrently isolated for 2 years. All isolates belonged the same group, L. pneumophila serogroups 2-14. Isolates were all attributed by SBT to sequence type (ST) ST328, although PFGE revealed 5 different patterns. No significant change in antibiotic susceptibility could be observed for this study period, irrespectively of the method used.

CONCLUSION

Colonization of water systems by Legionella spp. is still occurring, although all the prevention rules were strictly followed. Antibiotic resistance monitoring may help us to find resistance in bacteria with environmental reservoirs but difficult to isolate from patients. The knowledge of the antibiotic susceptibility in environmental strains may help us to predict changes in clinical strains. This study might also help reconsidering Legionnaires' disease (LD) diagnostic methods. L. pneumophila serogroups 2-14 present all along the time of the investigation in the water distribution system can cause LD. However, they may not be detected by routine urine tests run on patients, thereby missing an ongoing LD infection.

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.

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.

Impact of water heater temperature setting and water use frequency on the building plumbing microbiome

Hot water plumbing is an important conduit of microbes into the indoor environment and can increase risk of opportunistic pathogens (for example, Legionella pneumophila). We examined the combined effects of water heater temperature (39, 42, 48, 51 and 58 °C), pipe orientation (upward/downward), and water use frequency (21, 3 and 1 flush per week) on the microbial composition at the tap using a pilot-scale pipe rig. 16S rRNA gene amplicon sequencing indicated that bulk water and corresponding biofilm typically had distinct taxonomic compositions (R²_Adonis=0.246, P_Adonis=0.001), yet similar predicted functions based on PICRUSt analysis (R²_Adonis=0.087, P_Adonis=0.001). Although a prior study had identified 51 °C under low water use frequency to enrich Legionella at the tap, here we reveal that 51 °C is also a threshold above which there are marked effects of the combined influences of temperature, pipe orientation, and use frequency on taxonomic and functional composition. A positive association was noted between relative abundances of Legionella and mitochondrial DNA of Vermamoeba, a genus of amoebae that can enhance virulence and facilitate replication of some pathogens. This study takes a step towards intentional control of the plumbing microbiome and highlights the importance of microbial ecology in governing pathogen proliferation.

Comparative analysis of solar pasteurization versus solar disinfection for the treatment of harvested rainwater

Background

Numerous pathogens and opportunistic pathogens have been detected in harvested rainwater. Developing countries, in particular, require time- and cost-effective treatment strategies to improve the quality of this water source. The primary aim of the current study was thus to compare solar pasteurization (SOPAS; 70 to 79 °C; 80 to 89 °C; and ≥90 °C) to solar disinfection (SODIS; 6 and 8 hrs) for their efficiency in reducing the level of microbial contamination in harvested rainwater. The chemical quality (anions and cations) of the SOPAS and SODIS treated and untreated rainwater samples were also monitored.

Results

While the anion concentrations in all the samples were within drinking water guidelines, the concentrations of lead (Pb) and nickel (Ni) exceeded the guidelines in all the SOPAS samples. Additionally, the iron (Fe) concentrations in both the SODIS 6 and 8 hr samples were above the drinking water guidelines. A >99% reduction in Escherichia coli and heterotrophic bacteria counts was then obtained in the SOPAS and SODIS samples. Ethidium monoazide bromide quantitative polymerase chain reaction (EMA-qPCR) analysis revealed a 94.70% reduction in viable Legionella copy numbers in the SOPAS samples, while SODIS after 6 and 8 hrs yielded a 50.60% and 75.22% decrease, respectively. Similarly, a 99.61% reduction in viable Pseudomonas copy numbers was observed after SOPAS treatment, while SODIS after 6 and 8 hrs yielded a 47.27% and 58.31% decrease, respectively.

Conclusion

While both the SOPAS and SODIS systems reduced the indicator counts to below the detection limit, EMA-qPCR analysis indicated that SOPAS treatment yielded a 2- and 3-log reduction in viable Legionella and Pseudomonas copy numbers, respectively. Additionally, SODIS after 8 hrs yielded a 2-log and 1-log reduction in Legionella and Pseudomonas copy numbers, respectively and could be considered as an alternative, cost-effective treatment method for harvested rainwater.

Copper-silver ionization at a US hospital: Interaction of treated drinking water with plumbing materials, aesthetics and other considerations

Tap water sampling and surface analysis of copper pipe/bathroom porcelain were performed to explore the fate of copper and silver during the first nine months of copper-silver ionization (CSI) applied to cold and hot water at a hospital in Cincinnati, Ohio. Ions dosed by CSI into the water at its point of entry to the hospital were inadvertently removed from hot water by a cation-exchange softener in one building (average removal of 72% copper and 51% silver). Copper at the tap was replenished from corrosion of the building's copper pipes but was typically unable to reach 200 μg/L in first-draw and flushed hot and cold water samples. Cold water lines had >20 μg/L silver at most of the taps that were sampled, which further increased after flushing. However, silver plating onto copper pipe surfaces (in the cold water line but particularly in the hot water line) prevented reaching 20 μg/L silver in cold and/or hot water of some taps. Aesthetically displeasing purple/grey stains in bathroom porcelain were attributed to chlorargyrite [AgCl(s)], an insoluble precipitate that formed when CSI-dosed Ag(+) ions combined with Cl(-) ions that were present in the incoming water. Overall, CSI aims to control Legionella bacteria in drinking water, but plumbing material interactions, aesthetics and other implications also deserve consideration to holistically evaluate in-building drinking water disinfection.

Combination of Heat Shock and Enhanced Thermal Regime to Control the Growth of a Persistent Legionella pneumophila Strain

Following nosocomial cases of Legionella pneumophila, the investigation of a hot water system revealed that 81.5% of sampled taps were positive for L. pneumophila, despite the presence of protective levels of copper in the water. A significant reduction of L. pneumophila counts was observed by culture after heat shock disinfection. The following corrective measures were implemented to control L. pneumophila: increasing the hot water temperature (55 to 60 °C), flushing taps weekly with hot water, removing excess lengths of piping and maintaining a water temperature of 55 °C throughout the system. A gradual reduction in L. pneumophila counts was observed using the culture method and qPCR in the 18 months after implementation of the corrective measures. However, low level contamination was retained in areas with hydraulic deficiencies, highlighting the importance of maintaining a good thermal regime at all points within the system to control the population of L. pneumophila.

Convective Mixing in Distal Pipes Exacerbates Legionella pneumophila Growth in Hot Water Plumbing

Legionella pneumophila is known to proliferate in hot water plumbing systems, but little is known about the specific physicochemical factors that contribute to its regrowth. Here, L. pneumophila trends were examined in controlled, replicated pilot-scale hot water systems with continuous recirculation lines subject to two water heater settings (40 °C and 58 °C) and three distal tap water use frequencies (high, medium, and low) with two pipe configurations (oriented upward to promote convective mixing with the recirculating line and downward to prevent it). Water heater temperature setting determined where L. pneumophila regrowth occurred in each system, with an increase of up to 4.4 log gene copies/mL in the 40 °C system tank and recirculating line relative to influent water compared to only 2.5 log gene copies/mL regrowth in the 58 °C system. Distal pipes without convective mixing cooled to room temperature (23-24 °C) during periods of no water use, but pipes with convective mixing equilibrated to 30.5 °C in the 40 °C system and 38.8 °C in the 58 °C system. Corresponding with known temperature effects on L. pneumophila growth and enhanced delivery of nutrients, distal pipes with convective mixing had on average 0.2 log more gene copies/mL in the 40 °C system and 0.8 log more gene copies/mL in the 58 °C system. Importantly, this work demonstrated the potential for thermal control strategies to be undermined by distal taps in general, and convective mixing in particular.

Water heater temperature set point and water use patterns influence Legionella pneumophila and associated microorganisms at the tap

BACKGROUND

Lowering water heater temperature set points and using less drinking water are common approaches to conserving water and energy; yet, there are discrepancies in past literature regarding the effects of water heater temperature and water use patterns on the occurrence of opportunistic pathogens, in particular Legionella pneumophila. Our objective was to conduct a controlled, replicated pilot-scale investigation to address this knowledge gap using continuously recirculating water heaters to examine five water heater set points (39-58 °C) under three water use conditions. We hypothesized that L. pneumophila levels at the tap depend on the collective influence of water heater temperature, flow frequency, and the resident plumbing ecology.

RESULTS

We confirmed temperature setting to be a critical factor in suppressing L. pneumophila growth both in continuously recirculating hot water lines and at distal taps. For example, at 51 °C, planktonic L. pneumophila in recirculating lines was reduced by a factor of 28.7 compared to 39 °C and was prevented from re-colonizing biofilm. However, L. pneumophila still persisted up to 58 °C, with evidence that it was growing under the conditions of this study. Further, exposure to 51 °C water in a low-use tap appeared to optimally select for L. pneumophila (e.g., 125 times greater numbers than in high-use taps). We subsequently explored relationships among L. pneumophila and other ecologically relevant microbes, noting that elevated temperature did not have a general disinfecting effect in terms of total bacterial numbers. We documented the relationship between L. pneumophila and Legionella spp., and noted several instances of correlations with Vermamoeba vermiformis, and generally found that there is a dynamic relationship with this amoeba host over the range of temperatures and water use frequencies examined.

CONCLUSIONS

Our study provides a new window of understanding into the microbial ecology of potable hot water systems and helps to resolve past discrepancies in the literature regarding the influence of water temperature and stagnation on L. pneumophila, which is the cause of a growing number of outbreaks. This work is especially timely, given society's movement towards "green" buildings and the need to reconcile innovations in building design with public health.

Modelling characteristics to predict Legionella contamination risk - Surveillance of drinking water plumbing systems and identification of risk areas

For the surveillance of drinking water plumbing systems (DWPS) and the identification of risk factors, there is a need for an early estimation of the risk of Legionella contamination within a building, using efficient and assessable parameters to estimate hazards and to prioritize risks. The precision, accuracy and effectiveness of ways of estimating the risk of higher Legionella numbers (temperature, stagnation, pipe materials, etc.) have only rarely been empirically assessed in practice, although there is a broad consensus about the impact of these risk factors. We collected n = 807 drinking water samples from 9 buildings which had had Legionella spp. occurrences of >100 CFU/100mL within the last 12 months, and tested for Legionella spp., L. pneumophila, HPC 20°C and 36°C (culture-based). Each building was sampled for 6 months under standard operating conditions in the DWPS. We discovered high variability (up to 4 log(10) steps) in the presence of Legionella spp. (CFU/100 mL) within all buildings over a half year period as well as over the course of a day. Occurrences were significantly correlated with temperature, pipe length measures, and stagnation. Logistic regression modelling revealed three parameters (temperature after flushing until no significant changes in temperatures can be obtained, stagnation (low withdrawal, qualitatively assessed), pipe length proportion) to be the best predictors of Legionella contamination (>100 CFU/100 mL) at single outlets (precision = 66.7%; accuracy = 72.1%; F(0.5) score = 0.59).

Post-Outbreak Investigation of Pseudomonas aeruginosa Faucet Contamination by Quantitative Polymerase Chain Reaction and Environmental Factors Affecting Positivity

OBJECTIVE

To perform a post-outbreak prospective study of the Pseudomonas aeruginosa contamination at the faucets (water, aerator and drain) by culture and quantitative polymerase chain reaction (qPCR) and to assess environmental factors influencing occurrence

SETTING

A 450-bed pediatric university hospital in Montreal, Canada

METHODS

Water, aerator swab, and drain swab samples were collected from faucets and analyzed by culture and qPCR for the post-outbreak investigation. Water microbial and physicochemical parameters were measured, and a detailed characterization of the sink environmental and design parameters was performed.

RESULTS

The outbreak genotyping investigation identified drains and aerators as the source of infection. The implementation of corrective measures was effective, but post-outbreak sampling using qPCR revealed 50% positivity for P. aeruginosa remaining in the water compared with 7% by culture. P. aeruginosa was recovered in the water, the aerator, and the drain in 21% of sinks. Drain alignment vs the faucet and water microbial quality were significant factors associated with water positivity, whereas P. aeruginosa load in the water was an average of 2 log higher for faucets with a positive aerator.

CONCLUSIONS

P. aeruginosa contamination in various components of sink environments was still detected several years after the resolution of an outbreak in a pediatric university hospital. Although contamination is often not detectable in water samples by culture, P. aeruginosa is present and can recover its culturability under favorable conditions. The importance of having clear maintenance protocols for water systems, including the drainage components, is highlighted.

Infect. Control Hosp. Epidemiol. 2015;36(11):1283–1291

Environmental (Saprozoic) Pathogens of Engineered Water Systems: Understanding Their Ecology for Risk Assessment and Management

Major waterborne (enteric) pathogens are relatively well understood and treatment controls are effective when well managed. However, water-based, saprozoic pathogens that grow within engineered water systems (primarily within biofilms/sediments) cannot be controlled by water treatment alone prior to entry into water distribution and other engineered water systems. Growth within biofilms or as in the case of Legionella pneumophila, primarily within free-living protozoa feeding on biofilms, results from competitive advantage. Meaning, to understand how to manage water-based pathogen diseases (a sub-set of saprozoses) we need to understand the microbial ecology of biofilms; with key factors including biofilm bacterial diversity that influence amoebae hosts and members antagonistic to water-based pathogens, along with impacts from biofilm substratum, water temperature, flow conditions and disinfectant residual—all control variables. Major saprozoic pathogens covering viruses, bacteria, fungi and free-living protozoa are listed, yet today most of the recognized health burden from drinking waters is driven by legionellae, non-tuberculous mycobacteria (NTM) and, to a lesser extent, Pseudomonas aeruginosa. In developing best management practices for engineered water systems based on hazard analysis critical control point (HACCP) or water safety plan (WSP) approaches, multi-factor control strategies, based on quantitative microbial risk assessments need to be developed, to reduce disease from largely opportunistic, water-based pathogens.