Legionella pneumophila levels and sequence-type distribution in hospital hot water samples from faucets to connecting pipes
Graphical abstract
Introduction
A marked increase in Legionella pneumophila infections has been reported over the last decade, as shown by the 286% increase in cases of legionellosis observed in the US between 2000 and 2014 (Garrison et al., 2016). Similarly, the number of Legionnaires’ disease cases in Europe steadily increased between 2011 and 2016, with 81% of these due to L. pneumophila (European Centre for Disease Prevention and Control (ECDC) (2017)). An estimated mortality rate of 8% has been associated with legionellosis (Centers for Disease Control and Prevention (CDC) 2017, European Centre for Disease Prevention and Control (ECDC) 2017), reaching as high as 25% in healthcare-associated outbreaks (Soda et al., 2017). In the United States, Legionella was the most-reported cause of outbreaks associated with drinking water from 2013 to 2014, causing the majority of hospitalizations (88%) and all deaths associated with drinking water outbreaks (Benedict et al., 2017). Legionella is known to proliferate in engineered water systems, such as cooling towers and large-building water distribution systems (Buse et al., 2012). Although cooling-tower associated outbreaks generally result in larger case clusters, potable water is nevertheless the most frequent reported source of exposure resulting in an infection by L. pneumophila (Garrison et al., 2016).
Opportunistic microbial pathogens are present and can be amplified in the plumbing system of large buildings, posing a health risk for vulnerable individuals. Conditions present in the plumbing of large buildings, such as elevated stagnation, sporadic water use, variable hydraulic regimes, large surface-to-volume ratios, biofilm formation and variable temperatures can provide favorable conditions for L. pneumophila (Flemming and Bendinger, 2014). In healthcare facilities, hot water systems feeding taps and showers are reported to have a higher prevalence of L. pneumophila relative to other Legionella species (Bargellini et al., 2011; Boppe et al., 2016; Marchesi et al., 2011). High levels of contamination measured at the point of utilization suggests a distal amplification of L. pneumophila of up to 100-fold compared to levels in the hot water system (Boppe et al., 2016; Cristina et al., 2014). Similarly, heterotrophic plate counts (HPCs) can increase 1 to 3 log-fold in distal volume samples compared to levels found in 2–5-min flushed water, depending on the system configuration and prior stagnation (Bagh et al., 2004; Bédard et al., 2018; Cristina et al., 2014; Lautenschlager et al., 2010). The source of Legionella at distal points of the system, such as the faucet and its immediate connecting pipes, is primarily the hot water system (Bédard et al., 2016b; Cristina et al., 2014) and possibly the cold water system (Donohue et al., 2014; Marciano-Cabral et al., 2010; Pryor et al., 2004). Several potential causes of L. pneumophila amplification in hot water systems have been identified, including materials favorable to biofilm growth (Lu et al., 2014; Moritz et al., 2010), stagnation (Lu et al., 2017; Rhoads et al., 2015), and (most frequently) temperature and copper concentrations (Boppe et al., 2016; Dai et al., 2018; Lu et al., 2014). In a large building hot water system, these factors generally vary across the system, especially environmental factors like residual oxidants, copper concentrations and temperature, which often closely reflect stagnation. Furthermore, the selective amplification of distinct L. pneumophila strains between the faucet, its connection piping and the hot water system has not been established. Additionally, it is not known whether different L. pneumophila sequence types can be recovered in distal vs. flushed samples, or if strain selection varies from one faucet to another.
Municipal and building water systems can be colonized by multiple L. pneumophila sequence types (STs). Several studies have reported a low number of dominant environmental strains within a system (Byrne et al., 2018; David et al., 2017; Levesque et al., 2014; Oberdorfer et al., 2008; Qin et al., 2014). The prevalence of one ST can be driven by its superior adaptation to the specific conditions within its environment. Adaptation to new man-made environmental niches may be responsible for the recent independent geographical emergence of a few dominant disease-causing STs (David et al., 2016). Strains exposed to drinking water stressors, such as nutrient-poor conditions, high temperatures, and high copper and chlorine levels may adapt to these conditions and thrive in this environment over time (Al-Bana et al., 2014; Allegra et al., 2011; Boppe et al., 2016; Cervero-Arago et al., 2015). The infectivity of such environmental strains is often unknown, especially in the absence of detected clinical cases (Sharaby et al., 2018; Sousa et al., 2018). Conversely, the presence of host cells and the capacity of L. pneumophila strains to multiply within these cells may increase levels of contamination and risk of infection.
The main objective of this study was to compare L. pneumophila levels of contamination and strain diversity between the faucet and the hot water system in a hospital wing with elevated L. pneumophila contamination. Understanding the distribution of L. pneumophila contamination from faucets to system piping and if certain sequence types are specific to the faucet volume, will allow the optimization of corrective measures. The secondary objectives were to: 1) quantify the presence of L. pneumophila in various sections of the hot water system using profile sampling; 2) evaluate the impact of a system intervention to increase temperature on the STs recovered in distal and flushed samples; 3) evaluate the tolerance of prevalent STs to copper and control temperature exposure; and 4) verify the potential for infectivity of the prevalent STs.
Section snippets
Environmental sampling
This study was performed in the summer of 2016 in a ten-story, 450-bed hospital fed by chlorinated surface-filtered drinking water. The mean incoming municipal water temperature was 26.2 °C, with a measured residual chlorine level of 0.4 mg Cl2/L, an average heterotrophic plate count of 9.5 CFU/mL, and 1.8 × 103 viable cells/mL. The mean water temperature directly out of the boiler feeding into the hot water system was 61.6 °C, with very low residual chlorine concentrations (≤0.1 mg Cl2/L). Hot
Microbial characterization of investigated faucets
Levels of viable and total cells were not significantly different between the different consecutive volumes sampled from the different faucets (Fig. 2). In general, HPC values in the first 2 L sampled were significantly different than those obtained after 2 and 5-min flushing (p = 0.03, Fig. 3). HPC levels and profiles were comparable before and after the system intervention for faucets F1 and F2. However, the HPC level was significantly different between F1 and F2 (p = 0.005), suggesting a
Discussion
Distal amplification was observed for HPC and viable cells in the investigated faucets, as previously reported (Bédard et al., 2018; Cristina et al., 2014; Lautenschlager et al., 2010). The higher contamination of the distal point is generally attributable to prolonged stagnation at the point of use between usages, a large surface to volume ratio (promoting biofilm growth) and nonoptimal water temperatures (Bédard et al., 2018; Lautenschlager et al., 2010). In the principal and secondary
Conclusions
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L. pneumophila contamination was detected at similar concentrations throughout the hot water system of the examined hospital wing, from the faucet to the main horizontal flow and return loop. Contamination was not only distal but also associated with secondary flow and return loops, reflecting deficient temperature control across this wing.
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Only two STs (ST378 and ST154-like) were recovered from the study samples. The dominance of the non-sg1 ST378 was observed consistently between faucet and
Declaration of interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Acknowledgements
This study was supported by the partners of the NSERC Industrial Chair on Drinking Water. The authors would like to thank the Chair staff and students, especially Jacinthe Mailly, Catherine Taillandier, Margot Doberva and Wendy Andriantsarafara, for their help with sampling and lab analyses.
References (50)
- et al.
Distribution of bacteria in a domestic hot water system in a Danish apartment building
Water Res.
(2004) - et al.
Parameters predictive of Legionella contamination in hot water systems: association with trace elements and heterotrophic plate counts
Water Res.
(2011) - et al.
Prevalence of Legionella in premise plumbing in Hungary
Water Res.
(2016) - et al.
Investigative approach to improve hot water system hydraulics through temperature monitoring to reduce building environmental quality hazard associated to Legionella
Build. Environ.
(2016) - et al.
LIVE/DEAD® BacLightTM: application of a new rapid staining method for direct enumeration of viable and total bacteria in drinking water
J. Microbiol. Methods
(1999) - et al.
Legionellae in engineered systems and use of quantitative microbial risk assessment to predict exposure
Water Res.
(2012) - et al.
Comparison of clinical and environmental isolates of Legionella pneumophila obtained in the UK over 19 years
Clin. Microbiol. Infect.
(2007) - et al.
Overnight stagnation of drinking water in household taps induces microbial growth and changes in community composition
Water Res.
(2010) - et al.
Effectiveness of different methods to control legionella in the water supply: ten-year experience in an Italian university hospital
J. Hosp. Infect.
(2011) - et al.
Integration of Pseudomonas aeruginosa and Legionella pneumophila in drinking water biofilms grown on domestic plumbing materials
Int. J. Hyg Environ. Health
(2010)