July 5 (UPI) — An outbreak of Legionnaires’ disease on the Upper East Side of Manhattan in New York City has jumped to 14 confirmed cases, health officials said Sunday.

What began as a report of just two cases on Thursday has now increased sevenfold to cover three ZIP codes in the area, NYC Health Commissioner Dr. Alister Martin said in an update.

“As of July 4, there are 14 confirmed cases related to the Legionnaires’ disease community cluster on the Upper East Side,” he said. “At least one of those cases is a person who lives, works, or has visited the ZIP code 10075.

“As a result, The NYC Health Department is adding this ZIP code to the investigation area with 10028 and 10128.”

Martin advised people in the Carnegie Hill and Yorkville neighborhoods to be on the look-out for flu-like symptoms and to contact a healthcare provider immediately if they occur.

The warning also covers anyone who visited the east side of Central Park from East 76th to East 97th Street, he added.

“We identified the cluster early when there were just two confirmed cases, and we’ve acted swiftly and decisively, setting holiday plans aside to step up for our fellow New Yorkers,” the health official said.

“There is more work to do in the days ahead as we learn more about the source of exposure and confirmed cases.”

To date, there are no deaths associated with the cluster.

Legionnaires’ disease is a severe form of pneumonia that occurs from inhaling water droplets from manmade water systems contaminated with Legionella bacteria, usually traced to cooling towers.

In 1976, an outbreak of pneumonia caused 34 deaths at a 1976 American Legion Convention in Philadelphia, leading to the infection for this type of pneumonia to be named Legionnaire’s disease.

The latest cases come a year after seven people died and 90 were hospitalized due to a Legionnaire’s outbreak in central Harlem.

Investigators in that incident matched the Legionella strain found in victims to cooling towers at two locations, including Harlem Hospital and a nearby construction site.