New York City health officials said Thursday that initial testing has identified multiple “buildings of interest” in an investigation into a Legionnaires’ disease outbreak on the Upper East Side.

"While more extensive testing is underway to identify the specific source of exposure, The NYC Health Department is ordering all buildings to clean and disinfect their cooling towers based on the initial screening test results, which helps guide our investigation," a Health Department spokesperson said. 

The department said it will issue a list of “buildings of interest” “in the coming days.”

Officials say it is safe to be inside buildings that are under investigation, and to use those buildings’ water and air conditioning systems. They added that cooling towers spread Legionella bacteria through outdoor air, not inside the buildings.

As of Wednesday, the Health Department had confirmed 36 cases of Legionnaires' disease, including 22 hospitalizations. No deaths have been reported.

The outbreak is centered in the Carnegie Hill and Yorkville neighborhoods, covering ZIP codes 10028, 10128 and 10075.

Legionnaires’ disease is a type of pneumonia that’s caused by Legionella bacteria, which thrive in warm water. Among the possible symptoms are a cough, fever, muscle aches and difficulty breathing. It is not contagious and cannot be spread from person to person.

Adults age 50 and older, people who smoke or vape, people with chronic lung disease, people with weakened immune systems or people taking medications that suppress the immune system are most at risk, according to the DOH.

A Legionnaires' disease outbreak in Central Harlem last summer sickened more than 100 people and killed seven.