Towers for 76 buildings on New York's Upper East Side tested positive for Legionella bacteria, and their owners were ordered to drain, clean and disinfect them. (Photo Credit: BSIP/Universal Images Group Editorial/Getty Images via CNN Newsource)

(CNN) — A fourth person has died in connection with a cluster of Legionnaires’ disease cases in New York City, city health officials said.

As of Monday, 76 cases have been reported, and seven people are still hospitalized, the city’s health department said. Fifty-three people who were previously hospitalized have been discharged.

Officials believe that the cases are connected with bacteria found in building cooling towers on the Upper East Side. Towers for 76 buildings tested positive for Legionella bacteria, and their owners were ordered to drain, clean and disinfect them.

City officials said Monday they believe the source of exposure has been eliminated, with New York City Mayor Zohran Mamdani saying it was “due to the aggressive strategy of early testing, enforcement, and remediation.”

“We have not seen anyone with new symptoms in over a week. We are focused on inspecting every cooling tower that tested positive and enforcing our laws to their fullest extent,” Health Commissioner Dr. Alister Martin said in a post on X Monday.

The city said earlier that all 76 buildings confirmed they had completed the required remediation. There has been a sharp decline in illnesses beginning after July 8, the city health department said.

Last year, a community cluster of cases in Harlem sent 92 people to the hospital and killed seven. Those cases were connected to cooling towers, prompting the city to enact a law in May that requires more frequent inspections of the equipment and increased fines for property owners that failed to comply.

Cooling towers, used for refrigeration and general building cooling, expel building heat into the atmosphere by pulling outside air through warm water from a central chiller that gets sprayed over a fill material. As fans pull air through the water, a small amount evaporates, cooling the remaining water, which recirculates to take up more heat. People can get sick when they are exposed to vapor from those systems if there’s bacteria in it.

Studies show that cooling towers and other warm, wet environments like hot tubs, spas, fountains and some plumbing systems are particularly vulnerable to Legionella bacteria.

Public health officials noted that this particular cluster of cases is not connected to drinking water, showers or air conditioners.

New York sees hundreds of Legionnaires’ cases every year, but officials have noticed a spike in cases clustered in three particular ZIP codes: 10128, 10028 and 10075. Anyone who has been in that area in the past couple of weeks is advised to watch for symptoms such as fever, chills, fatigue, headaches, low appetite, confusion and diarrhea.

Legionnaires’ disease is not contagious, and it can be managed if people are given antibiotics early in the course of the disease.

Most people who are exposed to Legionella bacteria don’t get sick at all, but people can get sick after high or repeated exposure, especially in vulnerable groups that can include people who are over 50, who vape or smoke, or who have weakened immune systems or underlying health conditions like diabetes or heart, kidney, liver or lung disease.

There is no vaccine or medicine to prevent it, and masks don’t seem to offer protection, the New York health department said.

This story has been updated with additional information.

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