Outbreaks of the deadly Legionnaires’ disease are on the rise throughout the country, and deaths in Illinois, California, and New York have drawn a growing amount of attention from the media. According to a report from ABC News, the disease is caused by the Legionella bacteria and can spread though the air up to seven miles.

The disease was first discovered in Philadelphia at a convention for the American Legionnaires in 1976. The CDC reports that the number of outbreaks this year are not much higher than normal, but the concern arises from the fact that each outbreak is resulting in more infections.

The bacteria can lead to pneumonia, which wreaks havoc on the body’s respiratory system. They grow in warm water and spread throughout air conditioners, water fountains, hot tubs, and large plumbing systems. The bacteria cause infection when they are inhaled, but the disease is not contagious between people.

The CDC thinks that the increase could be caused by an actual rise in the frequency of the disease, which would be caused by an aging population and environmental factors. They also think that improved detection methods could explain the statistical rise in the disease.

So far, outbreaks of the disease have left 12 dead in New York City and at least 100 infected. 9 people in Illinois died from an outbreak of the disease, and six inmates in a California prison were confirmed to have the disease. New York City officials will be rushing to test city buildings over the next two weeks in an effort to identify the source of the bacteria.