NYC Experiencing Cluster of Legionnaires’ Disease

The New York City Health Department released a preliminary list of 31 buildings with cooling towers that tested positive for the presence of Legionella bacteria. The city identified the buildings during an initial polymerase chain reaction (PCR) screening test as part of the ongoing investigation into an Upper East Side Legionnaires’ disease community cluster that has sickened at least 46 people as of July 9.

Every building identified has been ordered to clean and disinfect its cooling tower immediately out of an abundance of caution, and remediation was completed for all buildings on the list by July 11. Additional PCR testing results were available over the weekend, and more buildings may be added to the list.

A positive PCR test result does not confirm that a building is the source of the outbreak. PCR testing detects the presence of Legionella bacteria but cannot determine whether the bacteria are alive or dead. Only live Legionella bacteria can cause illness, NYC health officials said.

To determine whether live Legionella bacteria were present when the samples were collected, the NYC Health Department is conducting culture testing on every cooling tower sampled. Those results take up to two weeks and will help investigators determine whether any of the cooling towers had live Legionella growing at the time the sample was taken. Cooling towers, which release water mist in the outside air, have been identified as the source of previous Legionnaires’ disease community clusters.

Following new emergency measures announced in response to this community cluster, the NYC Mayor Zohran Kwame Mamdani administration is requiring owners of buildings whose cooling towers have received a positive PCR screening result to clean and disinfect those cooling towers immediately, rather than waiting for confirmatory culture test results. The Mamdani administration is requiring building owners to perform a full cleaning and disinfection immediately after a positive PCR screening test, a more aggressive strategy than requiring a boost of chemical disinfectant levels while awaiting for a culture testing to confirm the presence of live Legionella bacteria before conducing t a full cleaning.

The NYC Health Department also has expanded capacity to respond to Legionnaires’ disease clusters by increasing community outreach, inspections, disease surveillance, and laboratory testing.

On July 2, the NYC Health Department identified two confirmed Legionnaires’ disease cases in close proximity  and immediately launched an investigation in the Upper East Side neighborhoods of Carnegie Hill and Yorkville, including ZIP codes 10028 and 10128.

On July 5, the Department expanded the investigation to include ZIP code 10075 after confirming an additional case involving a person who lives, works, or has visited that area.

As of July 9, 46 people have been diagnosed with Legionnaires’ disease in connection with this cluster. Twenty-two remain hospitalized, 19 have been discharged and are now recovering at home, and five were not hospitalized. There have been no deaths associated with this cluster.

Because symptoms can develop up to 14 days after exposure, the NYC Health Department expects additional cases may be identified for two weeks after the source of exposure has been eliminated.

As part of its investigation, the NYC Health Department has collected water samples from more than 180 cooling towers and found 31 buildings with positive results for the presence of the type of Legionella bacteria that causes Legionnaires’ disease.