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Legionella and other opportunistic pathogens in chloraminated drinking water distribution systems
Citation:
Zhang, C., I. Struewing, J. Mistry, D. Wahman, J. Pressman, AND J. Lu. Legionella and other opportunistic pathogens in chloraminated drinking water distribution systems. ACEER 2020, Virtual, October 20 - 23, 2020.
Impact/Purpose:
Drinking water quality may have public health implications. Monitoring microbial water quality is critical to estimate the microbe-associated health risks of drinking water. However, a group of natural inhabitants of drinking water, opportunistic pathogens (OPs), occurs in DWDSs at high densities, frequently causes water-related disease outbreaks, and is thus a major microbial factor threatening public health. Therefore, closely monitoring microbial water quality in DWDSs, especially the dynamics of OPs, is an urgent task for the water industry to better protect public health. Legionella is a key natural inhabitant in DWDSs with relatively high densities and correlates with important microbial (e.g., amoebae and biofilms) and physicochemical (e.g., disinfectant residuals) water quality parameters. For instance, Legionella and major OPs in DWDSs share multiple key features such as disease-causing, disinfectant resistance, biofilm formation, and proliferation in amoebae. Thus, we propose that Legionella can be an indicator for drinking water microbial water quality. Researches from institutes and managers from utilities could be interested in the results.
Description:
Waterborne opportunistic pathogens (OPs), like Legionella, continue to be one of the leading causes of drinking water related disease outbreaks. Other OPs also pose significant human health risk, but limited information is known about these microorganisms. To control and minimize the contamination, colonization, and overall presence of these OPs in municipal drinking water distribution systems (DWDSs), sufficient disinfectant residuals need to be maintained. However, the relationships between OPs, disinfectant residuals, and other physicochemical water quality parameters remain unclear. This study focuses on the interplay between OPs and the various physicochemical water quality parameters in four chloraminated DWDSs monitored in the United States. For all four DWDSs, the presence of Legionella, Mycobacterium, Pseudomonas, Vermamoeba vermiformis, and total bacterial densities were monitored using real-time quantitative PCR; in addition, estimated hydraulic retention time (HRT), water temperature, and concentrations of chloramines, ammonia, and disinfection byproducts (DBPs) were acquired. Results revealed that Legionella were the dominant organisms detected (4.27 × 105 ± 1.50 × 106 gene copy number · L-1) which occurred in 93.8% of the samples (n = 128) tested. Legionella concentrations also positively correlated with levels of Mycobacterium, Pseudomonas, and total bacterial densities in all four systems evaluated. Multiple regression analysis over four-utility data showed significant correlations (R2=0.55 and p<0.0001) between Legionella concentrations and water quality parameters: total chlorine residual, DBPs, water temperature, and free ammonia concentration. Moreover, the overall OPs densities displayed strong seasonal variations which peaked during the winter and/or spring season. Other findings revealed a strong correlation between OPs densities and HRT in the distribution systems, presumably due to pathogen (re-)growth and/or the loss of disinfectant residual. The densities of Mycobacterium, Pseudomonas, and V. vermiformis also showed associations to a certain extent with the concentrations of total chlorine, free ammonia, and DBPs, respectively. Chloramine residual levels between 2 to 4 mg Cl2·L-1 were correlated with reduced overall OP densities and presumably suppressed OP (re-)growth. This study provides additional insights into our understanding on the importance of maintaining disinfection residuals throughout the DWDS for controlling OPs. More importantly, it also suggests that Legionella, and perhaps other OPs, can be used as indicator organisms for assessing drinking water quality and efficacy of disinfectant residuals in municipal DWDSs.
