Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104, USA.
Yale University, New Haven, CT 06520, USA.
Water Res. 2018 May 1;134:261-279. doi: 10.1016/j.watres.2017.12.022. Epub 2017 Dec 13.
The use of reclaimed water brings new challenges for the water industry in terms of maintaining water quality while increasing sustainability. Increased attention has been devoted to opportunistic pathogens, especially Legionella pneumophila, due to its growing importance as a portion of the waterborne disease burden in the United States. Infection occurs when a person inhales a mist containing Legionella bacteria. The top three uses for reclaimed water (cooling towers, spray irrigation, and toilet flushing) that generate aerosols were evaluated for Legionella health risks in reclaimed water using quantitative microbial risk assessment (QMRA). Risks are compared using data from nineteen United States reclaimed water utilities measured with culture-based methods, quantitative PCR (qPCR), and ethidium-monoazide-qPCR. Median toilet flushing annual infection risks exceeded 10 considering multiple toilet types, while median clinical severity infection risks did not exceed this value. Sprinkler and cooling tower risks varied depending on meteorological conditions and operational characteristics such as drift eliminator performance. However, the greatest differences between risk scenarios were due to 1) the dose response model used (infection or clinical severity infection) 2) population at risk considered (residential or occupational) and 3) differences in laboratory analytical method. Theoretical setback distances necessary to achieve a median annual infection risk level of 10 are proposed for spray irrigation and cooling towers. In both cooling tower and sprinkler cases, Legionella infection risks were non-trivial at potentially large setback distances, and indicate other simultaneous management practices could be needed to manage risks. The sensitivity analysis indicated that the most influential factors for variability in risks were the concentration of Legionella and aerosol partitioning and/or efficiency across all models, highlighting the importance of strategies to manage Legionella occurrence in reclaimed water.
再生水的使用给水质维护和可持续性提高带来了新的挑战。由于在美国，其在水源性疾病负担中的比重不断增加，因此人们越来越关注机会性病原体，尤其是嗜肺军团菌。当人们吸入含有军团菌的雾气时，就会发生感染。本研究采用定量微生物风险评估（QMRA），对产生气溶胶的三种主要再生水用途（冷却塔、喷雾灌溉和马桶冲洗）进行了评估，以确定再生水中军团菌的健康风险。利用来自 19 家美国再生水公用事业公司的数据，通过基于培养的方法、定量 PCR（qPCR）和溴化乙锭单叠氮-qPCR 进行了风险比较。考虑到多种马桶类型，马桶冲洗的年平均感染风险中位数超过了 10，而临床严重感染风险中位数未超过此值。喷头和冷却塔的风险取决于气象条件和操作特性，如除雾器的性能。然而，风险情景之间的最大差异归因于：1）使用的剂量反应模型（感染或临床严重感染）；2）考虑的风险人群（居住或职业）；3）实验室分析方法的差异。提出了用于喷雾灌溉和冷却塔的理论后退距离，以实现 10 的年平均感染风险水平。在冷却塔和喷头的情况下，军团菌感染风险在潜在的大后退距离下并非微不足道，这表明需要同时采取其他管理措施来管理风险。敏感性分析表明，对风险变异性影响最大的因素是所有模型中军团菌的浓度和气溶胶分配和/或效率，这突显了管理再生水中军团菌发生的策略的重要性。
