What the Newest Culture Results Show
The list of Upper East Side cooling towers confirmed to have contained live Legionella bacteria has nearly doubled in less than a week, according to the New York City Health Department's outbreak page.
The department now reports that 57 cooling towers at 56 buildings have tested culture positive, with 65 towers testing culture negative, based on the confirmatory culture results list dated July 25. On July 21, the department had reported 34 culture-positive towers at 33 buildings, with nine negatives and 140 results still pending.
In total, 183 cooling towers at 160 buildings have been tested in the investigation area covering Carnegie Hill and Yorkville, ZIP codes 10028, 10075 and 10128. Of those, 77 towers at 75 buildings were positive in the initial PCR screening.
The case count has also moved. The department's outbreak page listed 84 confirmed cases as of its July 22 update, up from the 82 announced in the July 21 press release. Five people have died, seven remained hospitalized, 59 had been discharged, and 13 were never hospitalized. Officials said on July 21 that no new cases had been diagnosed in six days and no one had reported new symptoms in more than 10 days.
What Culture Positive Does and Does Not Prove
This is the point where the science matters more than the number, and where the city's own language has been careful.
The Health Department runs two different tests. A PCR screening test detects Legionella DNA and cannot distinguish between live and dead bacteria. A confirmatory culture test determines whether live bacteria were present in the tower at the moment the sample was taken. Only live bacteria can cause illness.
A culture-positive result therefore confirms one narrow fact: this tower held living Legionella when it was sampled. It does not establish that the tower released bacteria into the air, that anyone was exposed to it, or that it is the source of the cluster. The department states this directly, noting that a culture-positive cooling tower may or may not be the source of exposure in the current cluster.
That is why the list can grow without the outbreak growing. Four towers on the July 21 list had actually screened PCR negative and then turned up culture positive, which is one reason the city ordered remediation based on screening results rather than waiting two weeks for cultures.
"Seventy-six buildings we know is a significant number, but we knew that that list would be long. There's a high concentration of cooling towers in the Upper East Side, and our initial screening tests cast a wide net," Health Commissioner Dr. Alister F. Martin said at a news conference reported by CNN. "These results are also indicative of just how common Legionella is in our built environment, and that's why we stay vigilant."
What Has Changed Since MedicalDaily's Last Report
MedicalDaily previously reported that a fifth person had died as the case count reached 82, with 34 towers confirmed culture positive and officials saying the source had "likely been eliminated."
Three things have changed since. The confirmed culture-positive count has risen to 57 towers at 56 buildings. The number of towers cleared as culture negative has risen from nine to 65, meaning most pending results have now returned. And the department's public language has firmed, with the outbreak page now stating that officials are confident the source of the bacteria has been eliminated.
What has not changed is the central gap. No single building has been publicly identified as the confirmed source of the cluster, and the department has not announced a genetic match between a patient isolate and a tower sample.
Who Still Needs to Watch for Symptoms
The clinical guidance has not been relaxed. Anyone who lives or works in the affected ZIP codes, or who has visited the area since late June, and who develops flu-like symptoms such as cough, fever or difficulty breathing should contact a health care provider immediately, according to the Health Department.
Legionnaires' disease is a form of pneumonia. Symptoms can include fever, chills, muscle aches, cough, headache, fatigue, loss of appetite, confusion and diarrhea, and can appear up to 14 days after exposure. It is treatable with antibiotics and most people recover with early treatment, which is why timing matters more than anything else in this cluster.
Risk is concentrated in people aged 50 and older, people who smoke or vape, people with chronic heart, lung, kidney or liver disease or diabetes, and people with weakened immune systems. Living or working in a building with a positive tower does not itself raise risk, because exposure in a community cluster comes from mist that travels outdoors.
The department has repeatedly emphasized that this cluster is not a plumbing problem. Residents in the affected ZIP codes can drink tap water, bathe, shower, cook, and use home air conditioners normally, and the disease does not spread person to person.
New Yorkers who need help finding a provider regardless of immigration or insurance status can use NYC Health + Hospitals or call 311 or 844-NYC-4NYC.
Developing Story Timeline
July 25, 2026: Health Department culture results list shows 57 cooling towers at 56 buildings culture positive and 65 towers culture negative.
July 22, 2026, 7:15 p.m.: Outbreak page posts 84 confirmed cases, five deaths, seven hospitalized.
July 21, 2026: Department announces a fifth death, 82 cases and 34 culture-positive towers at 33 buildings, with 140 results pending.
July 10, 2026: Department releases its first preliminary list of 31 buildings with PCR-positive towers and orders immediate cleaning.
July 2, 2026: Investigation opens after two confirmed cases are identified in Carnegie Hill and Yorkville.
What Remains Unknown and What Comes Next
The source building has not been confirmed. The department has not said whether laboratory matching between patient and environmental isolates is underway or complete. A small number of culture results remain outstanding, and the addresses list is updated as they return.
Case counts remain preliminary. Because symptoms can appear up to two weeks after exposure, additional cases diagnosed in the coming days would not necessarily indicate new exposure. MedicalDaily will monitor the department's daily updates, the confirmatory culture results list, and any announcement identifying a confirmed source.
Frequently Asked Questions
What is new in this update? The number of cooling towers confirmed to have held live Legionella has risen from 34 to 57, the number cleared as culture negative has risen from nine to 65, and the case count stands at 84 with five deaths.
Does a culture-positive tower mean that building caused the outbreak? No. The Health Department says a culture-positive tower may or may not be the source. The result only confirms live bacteria were present when the sample was taken.
Is it still safe to use tap water and air conditioning in the area? Yes. The department says this cluster is not related to building plumbing, and residents can drink tap water, shower, cook and use home air conditioners.
Who is most at risk? People aged 50 and older, smokers and vapers, people with chronic heart, lung, kidney or liver disease or diabetes, and people with weakened immune systems.
What symptoms should I watch for? Cough, fever, chills, muscle aches, headache, fatigue, confusion or diarrhea, appearing up to 14 days after exposure. Contact a provider promptly and mention possible Upper East Side exposure.
Is Legionnaires' disease contagious? No. It does not spread from person to person.
Where can I see the building list? The Health Department publishes an address list of culture-positive cooling towers on it Legionnaires' disease page and updates it as results return.
