How Legionella Spreads

Legionella bacteria grow in warm, stagnant water and spread when microscopic water droplets — aerosols — are inhaled. The bacterium does not transmit person-to-person. Building cooling towers, hot water systems, and decorative fountains are the most common sources. Once inhaled, the bacteria can cause Legionnaires' disease, a severe pneumonia, or the milder Pontiac fever.

Why NYC Is Especially Vulnerable

New York City's dense urban canopy of skyscrapers relies heavily on evaporative cooling towers for air conditioning. Each tower can release millions of water droplets per hour into surrounding air. Prior to Local Law 77 (2015), there was no mandatory registry or inspection regime — meaning towers could harbor Legionella for years undetected.

2026 Upper East Side Cluster — What Is Known

Three deaths have been confirmed as of July 2026. NYC DOHMH has released geographic hotspot maps and accelerated cooling tower inspections citywide. The specific source building had not been publicly identified as of the latest reporting. The cluster remains under active investigation.