Legionnaires' bacteria can lurk in unlikely places, and numbers are up in AZ. What to know

Arizona has reported an increase in legionellosis cases this year, surpassing the five-year average, but it has avoided a deadly outbreak like the one in New York City. In NYC, a cluster linked to a cooling tower has resulted in three deaths and over 60 illnesses. Legionellosis encompasses both Legionnaires' disease, a severe form of pneumonia, and Pontiac fever, a milder illness. The Arizona Department of Health Services has not disclosed how many cases are specifically Legionnaires' disease. According to federal health officials, most healthy individuals exposed to Legionella bacteria do not get sick, but risks rise in warm water environments.

Cooling towers, showerheads, and complex plumbing systems are common breeding grounds for the bacteria. The CDC notes that Legionella can thrive when conditions are warm and stagnant. In 2015, a Phoenix VA hospital relocated patients after finding elevated Legionella levels in its water system, although no illnesses were reported.