In New York City, people usually got Legionnaires’ disease by breathing in tiny droplets of water contaminated with Legionella bacteria, most often from cooling towers on large buildings. The disease is not spread person-to-person, and it is not caught by drinking water or by using air conditioning in the usual sense.
How the infection happens
Legionella grows in warm water and can become a problem when water is turned into mist or vapor. In New York City, that mist has often come from rooftop cooling towers, hot tubs, decorative fountains, shower systems, or other building water systems that were not properly maintained.
When a contaminated cooling tower sprays water into the air, people nearby can inhale the droplets and get sick. That is why outbreaks in the city often affect people in a specific neighborhood or cluster of buildings rather than spreading widely from person to person.
Why New York City has had outbreaks
New York City has many large buildings with cooling towers, and those systems can create the right conditions for Legionella if water sits warm and stagnant. Public health officials have said that when cases appear in the same area, the likely source is often a cooling tower, while cases in the same building are more often linked to the building’s hot water plumbing system.
That does not mean every NYC case came from the same source. Some outbreaks have been traced to cooling towers, while others were linked to plumbing or remained under investigation for a time.
What it is not
Legionnaires’ disease is not caught from another person coughing or sneezing. It also does not come from simply being near a building with air conditioning; the risk comes from inhaling contaminated water mist created by certain water systems.
In plain terms
The short answer is that people in New York City got Legionnaires’ disease by inhaling contaminated water mist, usually from building cooling towers or, in some cases, plumbing systems. The bacteria were in the water, the water became airborne, and people breathed it in.