Legionella present in nearly 20% of water samples, new test results found

Findings indicate Legionella present in sinks, showers, hoses and other drinking water outlets;
Broader testing and prevention policy is needed, says prevention alliance

WASHINGTON, Sept. 3, 2026 /PRNewswire/ -- Independent environmental sampling found Legionella bacteria, including live, culturable Legionella pneumophila serogroup 1 (LP1) present during the recent NYC outbreak in 17 percent of water samples from Upper East Side buildings in sinks, showers, hose bibs, and other points of potential exposure. The test results, commissioned by the Alliance to Prevent Legionnaires' Disease (APLD), were provided to the New York City Department of Health.

The testing, conducted for APLD by an independent consultant in mid-July, included 109 samples collected across zip codes 10128, 10028 and 10075 which the City identified as the outbreak area. Legionella was found in 19 buildings including in 10 exterior hose bibs, an initial point of entry for water from the municipal drinking water system into buildings, seven sinks, one shower and a decorative fountain. Positive samples had Legionella concentrations ranging from less than 1 to 390 CFU/mL, with Legionella pneumophila serogroup 1 identified in all three zip codes sampled.  The samples also demonstrated very low chlorine treatment residuals as well averaging only 0.12 mg/L, well below an EPA workgroup recommended level of 0.5 mg/L. The City's testing during the outbreak focused on cooling towers only, per the current regulations and policy focus. 

"New York City tested 183 cooling towers as part of its current investigation, yet it has not publicly identified comparable Legionella testing of distribution system water or building fixtures and plumbing systems before assuring residents it was safe to use," said Bob Bowcock, APLD board member, licensed water treatment operator and founder of Integrated Resource Management, a water system consulting group. "You cannot rule out a point of exposure you never tested. Cooling towers are only one part of a system that begins at the source and ends at the tap. Best practices recommendations for Legionnaires' disease prevention call for a comprehensive water management approach to be effective."

Testimony by APLD Board members at the September 2 NYC Council hearing questioned the city's focus only on cooling towers for Legionnaires' prevention. The findings from the test results raise a key question:Is New York's Legionnaires' prevention strategy too narrowly focused on one type of water equipment and certain healthcare facilities, while missing other exposure points in building water systems?

New York continues to carry one of the country's highest Legionnaires' burdens and the vast majority (96% per CDC) of Legionnaires' cases are sporadic, not tied to recognized outbreaks, suggesting prevention efforts must extend beyond high-profile clusters. And Legionnaires' cases in NY regularly hit the news tied to residential and other buildings including cases at NYCHA buildings in the Bronx, Harlem last winter and ongoing issues in the East Village in the last year alone. There are no protections currently in place to prevent these cases.

"Finding Legionella in a small, three-day sample of ordinary water fixtures across the outbreak area should be a wake up call for New York City health officials to conduct a more complete investigation of the water distribution system," said Bill McQuade, an APLD board member and immediate past-President of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). "These results demonstrate why no responsible investigation – or prevention strategy -- should focus exclusively on one risk factor. And while experts agree Legionnaires' disease is preventable, it requires a holistic and integrated approach"

Other states have adopted more comprehensive safeguards, including minimum disinfectant-residual standards for water treatment in public water systems, full building water management plans consistent with ASHRAE 188-2021, and more thorough epidemiological investigations. APLD has been supporting legislation at the state level that would put these source-to-tap policies in place modeled after a 2024 law passed in NJ and strong water quality regulations that have been in effect in Illinois since 2019.

"We encourage officials to adopt a more comprehensive Legionnaires' prevention plan following national recommendations and best practices given its toll in New York," said Bowcock.

The full testing report can be made available upon request.

About the Alliance to Prevent Legionnaires' Disease
Founded in 2016, the Alliance to Prevent Legionnaires' Disease is a Washington, D.C.-based nonprofit dedicated to reducing the occurrence of Legionnaires' disease through education, collaboration, public policy and science-based prevention strategies. APLD brings together experts in public health, engineering, medicine, water treatment, environmental health and industry to advance practical solutions that help prevent Legionnaires' disease before outbreaks and cases occur.

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SOURCE Prevent Legionnaires'