A growing cluster of Legionnaires' disease cases on Manhattan's Upper East Side has reached 14 confirmed infections, according to city health officials.

The New York City Health Department announced Sunday that ZIP code 10075 has been added to the investigation, joining ZIP codes 10028 and 10128.

Officials said people who live, work or have visited those neighborhoods since late June should monitor for symptoms and seek medical care if they become ill.

Legionnaires’ disease is a type of pneumonia caused by Legionella bacteria that thrive in warm water. Symptoms include cough, fever, muscle aches and difficulty breathing.

New York City Health Commissioner Dr. Alister Martin said officials expect the number of confirmed cases to increase as more people are tested.

"It's my expectation that we'll see more cases. Now why is that? It's because we just spent the weekend telling the city's doctors to test for this, the hospitals to test for this, the nurses to test for this disease," Martin said. "And so, my expectation is we're going to see more cases, and that is an example of the system working right — catching these people early and making sure to treat this."

No deaths have been linked to the current outbreak.

Health officials believe the source of the bacteria is likely a cooling tower in the affected area.

The department said the cases are not related to any building's plumbing system, and residents can continue using tap water, showering, bathing, cooking and running home air conditioning systems as usual.

The current cluster follows a Legionnaires' disease outbreak in Harlem last summer that sickened more than 100 people and killed seven.

The Health Department said anyone who needs help finding a health care provider can call 311 or 844-NYC-4NYC, regardless of immigration or insurance status.