Abstract
Premise plumbing conditions can contribute to low chlorine or chloramine disinfectant residuals and reactions that encourage opportunistic pathogen growth and create risk of Legionnaires’ Disease outbreaks. This bench-scale study investigated the growth of Legionella spp. and Acanthamoeba in direct contact with premise plumbing materials—glass-only control, cross-linked polyethylene (PEX) pipe, magnesium anode rods, iron pipe, iron oxide, pH 10, or a combination of factors. Simulated glass water heaters (SGWHs) were colonized by Legionella pneumophila and exposed to a sequence of 0, 0.1, 0.25, and 0.5 mg/L chlorine or chloramine, at two levels of total organic carbon (TOC), over 8 weeks. Legionella pneumophila thrived in the presence of the magnesium anode by itself and or combination with other factors. In most cases, 0.5 mg/L Cl2 caused a significant rapid reduction of L. pneumophila, Legionella spp., or total bacteria (16S rRNA) gene copy numbers, but at higher TOC (>1.0 mg C/L), a chlorine residual of 0.5 mg/L Cl2 was not effective. Notably, Acanthamoeba was not significantly reduced by the 0.5 mg/L chlorine dose.
Highlights
Legionella is the primary cause of waterborne disease outbreaks in the United States (USA), with more than 5000 cases of Legionnaires’ Disease (LD) reported annually and approximately 5000–45,000 unreported cases per year [1,2,3], costing nearly a half billion dollars in annual hospitalization costs in the United States [4]
Chlorine demand was quantified in four influent waters with two levels of pH and two levels of organic carbon
An illustrative Cl2 dose response curve was developed (Figure 3) for each influent water, by plotting the chlorine residual as a function of total chlorine dosed to each Simulated glass water heaters (SGWHs) and determining the residual yield
Summary
Legionella is the primary cause of waterborne disease outbreaks in the United States (USA), with more than 5000 cases of Legionnaires’ Disease (LD) reported annually and approximately 5000–45,000 unreported cases per year [1,2,3], costing nearly a half billion dollars in annual hospitalization costs in the United States [4]. Deficiencies within the premise plumbing system have been associated with 85% of LD outbreaks between 2000–2014, including a lack of adequate disinfectant residual (70%) and water storage in the optimal temperature range for Legionella growth (52%) [1]. These findings are consistent with other LD outbreak investigations, in which problems were traced to stagnant water tanks with disinfectant residuals levels
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