We recently reported that a Legionnaires’ disease outbreak has been reported in New York, California, and Illinois — and authorities think that climate change could be behind the spread of the potentially deadly disease.

Legionnaires was first discovered back in 1976, and in recent years cases have been rising at a steady pace. The number of outbreaks this year are at normal levels, but the Centers for Disease Control and Prevention say that there are more cases per outbreak, which is majorly concerning and downright mystifying. One possible explanation is alarming, at least for what it means for mankind’s future: Legionnaires’ disease may be boosted by global warming, according to an NBC News report.

The disease is most prevalent in the late summer and early fall, when the Legionella bacteria can spread more easily through the air, causing people to come down with pneumonia, which can kill children, the elderly, and those with compromised immune systems.

This strain of bacteria likes warm water and thrives in air condition cooling units, hot tubs, or plumbing systems.

The numbers have been nothing short astonishing: about 1,110 cases of Legionnaires’ disease were reported in 2000, and 3,522 were reported in 2009, based on a 2011 report from the CDC.

While the CDC ventured a guess that it may be due to improved testing, some experts doubt this explanation. The NBC News report qutoed Dr. David Fishman, who is a professor at the Dalla Lana School of Public Health at the University of Toronto. Fishman said that while climate change is difficult to pin down as a factor, it’s a plausible explanation. The bacteria likes warm temperatures, and that the more wet and humid weather is, the easier the bacteria would be able to thrive.

With climate change likely to result in hotter and stormier summers, it’s not a big stretch to think that outbreaks of Legionnaires’ will become more common, he siad.