A Legionnaires’ disease outbreak in New York City has already left at least 70 people sick and three dead. All of these cases have occured in Central Harlem, which made the New York City Department of Health and Mental Hygiene suspect that something was amiss about the mist being emitted by the cooling towers in the area. Testing of 11 cooling towers there subsequently revealed the presence of Legionella pneumophila bacteria, which the NYC DOHMH believes caused the outbreak.

Cooling towers are large rooftop structures that are part of building cooling systems. These towers help disperse heat from the buildings into the air in the form of a vapor or mist.

Although such cooling towers are not sterile envioronments, the mist that they emit shouldn’t normally contain dangerous microbes. But when any water source remains too stagnant for too long with too little cleaning and too little disinfection, too many different nasty things can grow in it. Legionella pneumophila is one of the more dangerous microbes that can enter and grow in such water.

Such contamination turn a cooling tower into a distribution system for Legionella. Therefore, if you inhale the resulting vapor or mist, you could end inhaling a whole lot of Legionella. From there the Legionella can get into your lungs.

Inhaling contaminated water droplets is the primary route of Legionella infection—not person-to-person transmission. When someone has legionellosis, you........

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