NYC Outbreak Brings Legionella into Spotlight

A Legionnaires’ disease (legionellosis) outbreak in a Manhattan neighborhood has resulted in at least 92 people testing positive and 6 deaths.

Legionnaires’ disease is spread by people breathing in tiny water droplets or mist contaminated with Legionella bacteria. The disease is not contagious and cannot spread between people, rather incidence is impacted by the levels of Legionella bacteria in the water source and its virulence. However, source confirmation is difficult because Legionella bacteria are ubiquitous in natural and man-made water systems, long incubation periods obscure timelines, and aerosolized bacteria can travel long distances.

As structures that contain water and a fan as part of centralized air-cooling systems for buildings or industrial processes, cooling towers are common sources of exposure. Thus, the NYC Health Department has been testing 183 cooling towers in 160 buildings in the area of the community cluster of illness. The department found:

• 77 cooling towers at 75 buildings tested PCR positive for the presence of Legionella bacteria in initial testing.
• 59 at 58 buildings tested culture positive, confirming the presence of live Legionella bacteria; all have been cleaned and disinfected.
• 106 have tested culture negative.
• All other results are pending at the time of this writing.

In the food industry, Legionella mainly comes from large industrial water systems that create airborne mists, with cooling towers, evaporative condensers, and produce misting systems serving as the primary risk areas. To reduce its growth and proliferation, facilities should:

• Thoroughly understand your building’s water system. Consider engaging professionals with expertise in detecting and effectively managing Legionella risks.
• Flush any water systems that have sat unused for long periods or are used infrequently.
• Ensure your water system is properly designed. The American Society of Heating, Refrigerating and Air-Conditioning Engineers( ASHRAE) [CD1] guidance includes elements such as avoiding dead legs in pipes or other areas that can allow water to sit for an extended time; treating water with heat and/or chemical disinfectants that hold claims against Legionella bacteria; incorporate turbulence to reduce biofilm formation.

The NYC Health Department is advising that anyone who lives or works in the Upper East Side neighborhoods of Carnegie Hill and Yorkville (ZIP codes 10028, 10128, and 10075) or has visited since late June who is experiencing flu-like symptoms (e.g., cough, fever, or difficulty breathing) should contact a health care provider immediately. 

For more information on Legionellosis, see TAG’s Infectious Disease Fact Sheet on Legionellosis.

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