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Legionella in 2026: two hotel outbreaks and New York's 31-day rule
Official documents this year change how a building team should read its own water system. The CDC's investigation of two hotel outbreaks found the bacteria in cold water and cisterns, not cooling towers, at temperatures a Florida or Caribbean property reaches every afternoon. New York City, after a cluster that killed 11 people, cut the legal interval between cooling tower Legionella tests from 90 days to 31. Then a second cluster, in the South Bronx in September, showed what the new interval does and does not do: eight of the ten towers the Health Department ordered cleaned had met the 31-day testing requirement.
The two hotels: what the samples showed
| Hotel A | Hotel B | |
|---|---|---|
| Positive samples | 3 of 21 (14%) | 22 of 40 (55%), 19 of them serogroup 1 |
| Where | All three in cold, unheated water: a shower, the cistern and the supply pipe; no hot-water sample was positive | Hot and cold water, plus swab samples |
| Temperature of positive samples | 80°F to 87°F | 82°F to 118°F |
| Chlorine | Free chlorine undetectable in 8 samples | Undetectable in 1 sample |
Four guests were diagnosed, two were hospitalized, none died. Both hotels drew on mixed supplies that included cisterns, which the report says can harbor pathogens and are hard to clean, monitor and disinfect. In tropical climates, cold water reaches the range where the organism grows, which the report gives as 77°F to 113°F. At hotel B the hot water system may not have reached a suppressing temperature, leaving disinfectant as the only control. An air conditioning unit sampled at hotel B was negative; cooling towers are not mentioned as a source.
The recommendations put numbers on the water management program: hot water stored above 140°F and circulated above 120°F, effective disinfection, cistern maintenance guidance, and notifying guests of a possible exposure.
New York: from 90 days to 31
The Upper East Side cluster of summer 2026 reached 94 cases and 11 deaths. The Health Department had 183 cooling towers in three ZIP codes tested over the July 4 weekend; 83 came back preliminary PCR-positive and every one was ordered drained, cleaned and disinfected. Compliance with the monthly testing requirement in the affected ZIP codes went from 74% on July 10 to 97% two weeks later; citywide, from 77% before the cluster to 81% by late August, across more than 5,000 towers. The central change of the local law that took effect May 8, 2026 was to move the required Legionella test "from once every 90 days to once every 31 days."
New York record and the NYC overlayASHRAE 188 in the Citation Decoder
The second cluster: South Bronx, September 2026
Four months after the 31-day rule took effect, the Health Department identified a second community cluster on September 10, 2026, in Melrose and Morrisania. Its three press releases give the sequence an owner should expect when a tower in the area tests positive.
| Date (2026) | What the Health Department reported |
|---|---|
| September 10 | Cluster identified; 24 cooling towers in the area sampled within 12 hours. |
| September 12 | Preliminary PCR results: 10 of the 24 towers positive. All 10 ordered drained, cleaned and disinfected by September 14. Of the 10, 8 had met the 31-day testing requirement in force since May 8; 2 had not provided the required testing information. |
| September 13 | 9 cases, 1 death. Citywide, 82% of cooling tower systems compliant with monthly testing; more than 900 inspections since May 8; more than $111,000 in fines paid as of September 5. |
| September 23 | Culture results: 7 of the 10 towers had live Legionella; all 7 had already been cleaned. 22 cases, 2 deaths. |
| September 30 | 23 cases, 2 deaths, 21 hospitalized, as of September 29. Source declared eliminated: no new symptomatic case in more than two weeks, every positive tower cleaned more than two weeks earlier. Whole-genome sequencing of patient and tower samples continuing, results expected by late fall. |
One sentence from the September 23 release states the department's practice: "When a cooling tower receives a positive test result of any kind, the Health Department orders the building owner to clean and disinfect the tower." The same release explains the test: the PCR screen detects Legionella DNA but cannot tell whether the bacteria are alive; culture takes up to two weeks, so towers are cleaned before a positive culture is confirmed. Three of the ten towers ordered cleaned in September turned out to have no live bacteria.
The previous edition of this page carried the Upper East Side cluster alone (94 cases and 11 deaths, as of August 31). The South Bronx cluster adds 23 cases and 2 deaths, as of September 29.
What this means for a hotel or a condominium
| Your building | What the documents add |
|---|---|
| Florida, Caribbean or Gulf coast, any size | Cold water is not safe by being cold. Log cold-water temperatures at distal outlets in summer; a reading in the 80s is the CDC's finding, not an anomaly. If there is a cistern or storage tank, it is part of the water management program. |
| Hot water system | The storage and return temperatures in your program should meet or exceed 140°F stored and 120°F circulating, with scald protection at the fixtures; if the system cannot, disinfectant residual is the only control and must be measured. |
| Cooling towers anywhere | New York's 31-day cadence is now the strictest in the country and is what other large cities will be asked about. A tower on a 90-day schedule should have a reason written down. |
| Cooling towers with a current test on file | In the South Bronx, 8 of the 10 towers ordered cleaned had met the 31-day requirement. A compliant testing record did not keep a tower off the order list, and it will not in another city that follows New York's practice of ordering a cleaning on any positive result. The September order gave owners two days (issued September 12, due September 14). The maintenance plan should say who drains, cleans and disinfects on that notice and who documents it; the health department's order sets the deadline and confirms compliance, and a qualified water-treatment contractor does the work. |
| Guest or resident cases | Both documents assume the building will notify people who may have been exposed; the plan should say who decides and how. |
A water management program under ASHRAE 188 is the framework both documents point to; confirm what your state or local health department requires, and have the program reviewed by a qualified water-treatment professional.
What is not on this page, and why
The CDC report names neither hotel. The Health Department published the addresses of the ten South Bronx towers it ordered cleaned; this page does not restate them. The New York local law's number is not stated in the testimony and is not repeated here until read on the Council's site. National case counts for 2026 are not yet published by CDC; its surveillance page, updated July 8, 2026, carries provisional 2024 and 2025 incidence in a figure without a printed total. Florida has no statewide cooling tower registration or testing law; county rules may apply and are in the county overlays of the Florida record.
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