New York City’s Upper East Side is facing a growing outbreak of Legionnaire’s disease, with health officials reporting 18 cases as of Monday—potentially impacting major tourist areas in the city, as officials warn visitors to Central Park are among those who should now be monitoring for symptoms.

People sunbathe during a heat advisory in Central Park on May 19.

New York health officials are investigating a suspected outbreak of Legionnaire’s disease covering the zip codes of 10028, 10128, and 10075—which spans roughly from 76th street to 96th street on the East Side of Manhattan—with 18 cases reported and no fatalities.

Legionnaire’s is a type of pneumonia that spreads when people inhale tiny water droplets infected with legionella, a type of bacteria, which the city notes is likely caused by cooling towers on the top of buildings.

Anyone who lives, works or has recently visited the impacted area should monitor for symptoms, city health officials said, including visitors to the East Side of Central Park between 76th Street and 97th Street.