New York City is experiencing yet another outbreak of Legionnaires’ disease—the second this year alone. Previous multiple clusters of infection have been recorded in 2015, 2016, 2017 and 2018. This time it is hitting the South Bronx, while the previous one, centered in the Upper East Side of Manhattan, took place in July, only two months ago. 

That outbreak, one of the city’s worst, killed a total of 11 people, with 90 officially recorded infections. So far, this new occurrence has caused two deaths with 22 reported infections, with three people currently hospitalized. Those figures are expected to rise as testing proceeds. As of Monday, September 22, the search for infections continues to expand to additional neighborhoods beyond the initial cluster. 

Legionella is caused by bacteria typically found in infected water droplets dispersed in air. The main source is thought to be rooftop cooling towers on large buildings with central air conditioning. The towers provide heat dissipation via transfer to water which is volatilized and dispersed into the surrounding air.

The water to be used for this process is kept in rooftop tanks. If the tanks are not drained and disinfected at frequent intervals, bacteria may accumulate and contaminate the water which then is spewed into the surrounding neighborhood’s air, to be inhaled by passersby, resulting in infection. Legionella bacteria thrive in warm water (77–113°F / 25–45°C) and stagnant or low-flow water systems. 

Direct, person-to-person transmission is not thought to occur, or perhaps to be very infrequent, so some other method of dispersal must spread the bacteria from place to place in neighborhoods that experience outbreaks, such as transfer of contaminated water. 

Legionnaires’ disease is a severe form of pneumonia characterized by fever, cough and difficulty breathing. Most cases can be treated with antibiotics, if caught soon enough. The people at highest risk include adults over 50, smokers and those with chronic lung disease or weakened immune systems. The incubation period is 2-14 days following inhalation. The disease occurs nationwide, with about 5,000 to 8,500 cases of Legionnaires’ disease diagnosed in the US each year. 

This past May, the new Mamdani administration mandated a 31-day cycle of testing rooftop water tanks for Legionella bacteria. During the latest outbreak, two of the buildings with positive tests were out of compliance with reporting requirements, indicating an insufficient level of enforcement. Health experts have proposed both stricter supervision of compliance with the revised testing protocol and more rapid response to identified contamination. 

The disease, first identified in 1976 during an outbreak at a Pennsylvania American Legion convention in Philadelphia, is an ongoing problem in New York City, which has an unusually high, chronic case rate. Approximately 200 to 700 people are diagnosed with the disease annually in the city, most of whom require hospitalization, with roughly a dozen cases resulting in death. 

Last year’s outbreak occurred in the city’s Harlem neighborhood, in northern Manhattan. According to the New York City Health Department, there were 114 confirmed cases, 90 hospitalizations and seven deaths. In 2015 in the South Bronx there were 138 reported infections and 16 deaths. A total of 257 cases were diagnosed in 2024.

A total of 24 cooling towers had been tested as of a week ago. So far, 10 buildings have tested positive for Legionella bacteria, a rate of 42 percent. If anything like that rate applies to a larger area in a densely populated city of over 8.5 million people, there would be serious danger of widespread contamination.

Types of construction vary widely, and therefore the potential for favorable conditions for Legionella bacteria is as yet unknown. But there is no question that effectiveness of measures to reduce the probability of outbreaks falls far short of what is needed, given the frequency of recorded incidents. 

The latest outbreak has a novel feature. In addition to cooling towers on residential buildings that have been found to be infected, positive results have also been found in cooling towers at Yankee Stadium, Lincoln Hospital and the Boricua College Bronx Campus. 

It is also alarming that New York City’s regulations in regard to Legionnaires’ disease are by far the strongest in the US. The dangers in other large cities could well be greater, and, given that the symptoms of Legionnaires could well be misdiagnosed as pneumonia, the current figure of 5,000 to 8,500 cases annually could be a sizeable underestimate.

The danger is also increased by the acceleration of global warming, which will, among other effects, increase the use of air conditioning. The capitalist crisis which is responsible for global warming is creating conditions for the increase in the spread, not only of Legionella but many other diseases as well, such as Ebola. Meanwhile, at the same time, healthcare is under attack around the world.