The Health Department reported today that at least two people have died and dozens have been sickened in the Bronx by Legionnaire's disease, an airborne bacterial infection that's similar to pneumonia.

According to authorities, 31 cases have been reported in the South Bronx since July 10th of this year, with High Bridge, Morrisania, Hunts Point and Mott Haven getting hit particularly hard. The Health Department has been unable to pinpoint the cause of the outbreak, but cautioned that the disease is often traced to water systems like hot tubs, humidifiers, hot water tanks, and large air-conditioning systems.

Two people have died of the illness so far. Authorities warn that middle-aged and elderly people are most at-risk for Legionnaire's disease, particularly if they are cigarette smokers—other high-prone groups include those with chronic lung disease or anyone who is immunocompromised.

“We are concerned about this unusual increase in Legionnaires’ disease cases in the South Bronx,” Health Commissioner Dr. Mary Bassett said in a statement. “We are conducting a swift investigation to determine the source of the outbreak and prevent future cases. I urge anyone with symptoms to seek medical attention right away.”

According to the Centers for Disease Control & Prevention, early symptoms include high fever, chills and a cough—muscle aches and headaches are also common. Symptoms begin about 2 to 10 days after a person is exposed the the bacteria, and mimic those of pneumonia.