An outbreak of Legionnaire’s disease has infected at least 46 in New York City and health officials said the bacteria has already been found in cooling units on top of at least two buildings.

Two patients with Legionnaire's disease died during the outbreak, but officials stressed that the two patients, a man and woman in their 50s, had other conditions including lung and heart issues.

Caused by a bacteria called Legionella, the infection causes a type of pneumonia that can be damaging or even fatal for those with compromised immune systems or underlying health conditions. It’s contracted when a person inhales small droplets of air or water with the bacteria and can be spread from contaminated hot tubs, fountains, cooling units for air conditioners and large plumbing systems.

Dr. Mary Basset, commissioner of the New York City Health Department said the bacteria which causes the disease has been found in two cooling towers in the Bronx, one in a hospital and one in a commercial buildings.

She stressed that the units did not lead to infections inside the buildings and explained at that as the cooling towers release mist it falls onto the street and can potentially infect those passing by.

“It thrives in water and in summer we have a better atmosphere for it,” explained Basset. “We are looking into ways to keep a better eye on the maintenance of these cooling towers.”

She said the reported cases were spread out in a large area so investigators were still searching for other sources of infection.

“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,” Bassett said in an earlier statement.

Symptoms of Legionnaire’s disease include coughing, shortness of breath, high fever, muscle aches or headaches.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University School of Medicine, said that 31 infections constitute a large outbreak for Legionnaire’s disease and that health officials will likely look for a common source if people are in the same neighborhood.

“If they are clustered geographically … Where do they travel, where do they work, where do they worship?,” Schaffner said of the kinds of questions health officials will ask patients. “By localizing it geographically you can look up and see if you can find cooling towers that might be contaminated.”

While the large outbreak is worrying, Schaffner said people should not panic since the disease cannot be spread person to person and antibiotic treatment is available.

The disease was named after it infected numerous people at conference of the American Legion in 1976. The bacteria leads to the hospitalization of around 8,000 to 18,000 people in the U.S. every year according to the U.S. Center of Disease Control and Prevention and it is more commonly reported in the summer and early fall.