Legionella spp. Monitoring in New York City’s Water Distribution System

Government Public Health and Private Environmental Laboratory Partnerships
Oral Presentation

Prepared by E. Omoregie1, A. Szczerba2, A. Capetanakis3, S. Freud4, J. Novak1, S. Hughes1, J. Rakeman1
1 - NYC Department of Health and Mental Hygiene, 455 First Ave., New York, NY, 10016, United States
2 - NYC Department of Environmental Protection, 9605 Horace Harding expw., , NY, Corona, United States
3 - NYC Department of Environmental Protection, 9605 Horace Harding Exprw., Corona, NY, Corona, United States
4 - NYC Department of Environmental Protection, 9505 Horace Harding Exprw, , NY, Corona, United States

Contact Information: [email protected]; 212-671-5786


Legionella, primarily Legionella pneumophila serogroup 1, is the causative organism for legionellosis and has received increased attention as a result of several highly publicized national outbreaks of Legionnaires disease. Legionella spp. are ubiquitous in aquatic systems and have been shown to be present in source and distribution waters. The presence of Legionella spp. in NYC’s drinking water distribution system has not been systematically investigated. Therefore, the NYC Department of Environmental Protection (DEP) and NYC Department of Health and Mental Hygiene (DOHMH) conducted a joint one-year longitudinal study to determine the prevalence and distribution of Legionella spp. in NYC source water and the distribution system.
Twelve monthly sampling events took place between November 2017 and October 2018. A total of 255 water samples were collected from 19 locations each month, representing water from NYC’s watersheds. Samples from different stages of water treatment were tested, including untreated source water, prefinished water and finished waters from various distribution sites including those with historically low residual chlorine levels and longest residence times. Physicochemical and microbial characteristics were measured for all samples and Legionella detection was conducted using PCR and culture methods.
All water samples met applicable (EPA and NYS) water quality guidelines for physiochemical and microbiological parameters, and. Legionella spp. were infrequently detected by culture. Legionella spp. DNA was detected by PCR in all (23/23) untreated source water samples, but Legionella DNA detection in prefinished and finished water samples was variable. In total, 88% (202/231) of the water samples had detectable Legionella spp. DNA, which is unsurprising given Legionella spp. are ubiquitous in aquatic environments. Despite frequent detection of Legionella DNA throughout the distribution system, only 2. 5% (6/231) of samples were culture positive. L. bozemanii (50 CFU/100 mL) was recovered in the same source water site on two occasions and L. pneumophila (1 - 20 CFU/100 mL) was recovered from the same distribution site on four occasions. Results did not indicate a correlation between L. pneumophila recovery and physicochemical changes within the distribution system. However, the positive distribution site was in the midst of an ongoing new main replacement and street construction project. Although Legionella DNA was detected throughout the distribution system, the lack of recoverable Legionella in samples collected in this study suggest these Legionella werenon-viable and that the current disinfection practices are effective in protecting against the presence of Legionella spp. in New York City’s water supply.