New York City's Legionnaires' disease outbreaks from Harlem to the Bronx

The Harlem cluster was detected on July 25, 2025, across several ZIP codes,^[8] and within days it had killed three people and sickened more than five dozen.^[1] By mid-August the city had confirmed 108 cases,^[4] and health officials later identified a city hospital and another city-run building as sources of the outbreak, which killed seven.^[3] A year later families of dozens of victims sued the city and contractors, saying they failed to maintain the cooling towers.^[9]

In early July 2026 cases appeared on the Upper East Side.^[10] Cooling towers at 31 buildings, including the Guggenheim Museum and a Whole Foods Market, tested positive for Legionella,^[11] and officials tied the cluster to towers on 76 buildings.^[2] Mayor Zohran Mamdani said the outbreak showed signs of slowing,^[12] but the first death was announced on July 17,^[13] and by the end of the month the toll reached seven, matching Harlem's.^[5] In September five people were diagnosed and one died in a likely cluster in the South Bronx, where Yankee Stadium was among the buildings investigated.^[6][14]