Health risks from exposure to Legionella in reclaimed water aerosols: Toilet flushing, spray irrigation, and cooling towers

Kerry A Hamilton; Mark T Hamilton; William Johnson; Patrick Jjemba; Zia Bukhari; Mark LeChevallier; Charles N Haas

doi:10.1016/j.watres.2017.12.022

Health risks from exposure to Legionella in reclaimed water aerosols: Toilet flushing, spray irrigation, and cooling towers

Water Res. 2018 May 1:134:261-279. doi: 10.1016/j.watres.2017.12.022. Epub 2017 Dec 13.

Authors

Kerry A Hamilton¹, Mark T Hamilton², William Johnson³, Patrick Jjemba³, Zia Bukhari³, Mark LeChevallier³, Charles N Haas⁴

Affiliations

¹ Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104, USA. Electronic address: kh495@drexel.edu.
² Yale University, New Haven, CT 06520, USA.
³ American Water Research Laboratory, 213 Carriage Lane, Delran, New Jersey 08075, USA.
⁴ Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104, USA.

PMID: 29428779
DOI: 10.1016/j.watres.2017.12.022

Abstract

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^-4 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^-4 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.

Keywords: Cooling towers; Legionella pneumophila; Quantitative microbial risk assessment (QMRA); Reclaimed water; Spray irrigation; Toilet flushing.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Aerosols / analysis*
Agricultural Irrigation
Environmental Monitoring
Humans
Legionella pneumophila / genetics
Legionella pneumophila / isolation & purification*
Legionellosis
Real-Time Polymerase Chain Reaction
Recycling*
Risk Assessment
Toilet Facilities
Water
Water Microbiology*

Substances

Aerosols
Water