A Legionnaires’ disease outbreak on Manhattan’s Upper East Side has grown to 23 confirmed cases, with several patients hospitalized in critical condition, New York City health officials announced Monday.

The number of confirmed infections has risen sharply from just two cases reported on July 2 and 14 cases reported Sunday.

Health Commissioner Dr. Alister Martin said many of the infected patients remain hospitalized, with several receiving treatment in intensive care units.

“We’ve had our first discharge,” Martin said, adding that officials are still in the early stages of the outbreak.

The Department of Health is investigating approximately 160 cooling towers in the affected area—including Yorkville and Carnegie Hill—to identify the source of the bacteria. About one-third of the towers have already been tested, and officials say any tower testing positive will be immediately remediated.

Residents who live or work in ZIP codes 10028, 10128, and 10075 are being urged to seek medical attention if they develop flu-like symptoms, particularly fever, cough, or difficulty breathing.

Health officials stressed that the outbreak is believed to be linked to contaminated cooling towers—not drinking water, residential plumbing, or home air conditioning systems.

Legionnaires’ disease is a severe form of pneumonia caused by Legionella bacteria spread through contaminated water vapor. The disease is not contagious and can usually be treated successfully with antibiotics, but it can become life-threatening if treatment is delayed. Adults over 50, smokers, and people with chronic lung disease or weakened immune systems are at greatest risk.

The investigation comes as city officials work to determine whether building owners complied with recently strengthened regulations requiring regular testing of cooling towers for Legionella bacteria.

(YWN World Headquarters – NYC)