New York City health officials are investigating an outbreak of Legionnaires' disease centered in parts of the Upper East Side after the number of confirmed cases rose to 23 as of July 6.Seventeen patients have been hospitalized, and several are reported to be in critical condition, although no deaths have been confirmed.

Most of the affected individuals either live, work, or recently visited neighborhoods including Yorkville and Carnegie Hill, as well as portions of Central Park between East 76th and East 97th streets.

Authorities are urging anyone who was in the area since late June and develops symptoms such as fever, chills, cough, muscle aches, or other flu-like illness to seek prompt medical care.

Legionnaires' disease is a severe form of pneumonia caused by Legionella bacteria, which grow in warm water systems and can spread through contaminated water droplets or mist from sources such as cooling towers, decorative fountains, hot tubs, and large plumbing systems.

Officials emphasized that the illness is not transmitted from person to person and that residents can safely drink tap water, shower, bathe, cook, and use home air conditioning.

Investigators are working to identify the environmental source of the outbreak, which they say has not yet been linked to a building's plumbing or air conditioning system.People over age 50, smokers, and those with chronic lung disease or weakened immune systems face the greatest risk of severe illness.

The outbreak follows previous Legionnaires' disease incidents in New York City, including a significant Harlem outbreak last year that resulted in multiple deaths and more than 100 reported infections.