A person has died in the Upper East Side Legionnaires' disease outbreak, the first death reported in a cluster that has now sickened dozens of people, city health officials said Friday.

At least 67 people have been diagnosed with Legionnaires' disease in connection with the outbreak, and 12 were hospitalized as of Thursday night, according to the city Health Department. Officials said they would not release any information about the person who died, citing the individual's privacy.

“My deepest condolences are with their loved ones,” Health Commissioner Dr. Alister F. Martin said.

Legionnaires' disease is a severe form of pneumonia caused by Legionella bacteria, which can grow in building water systems and spread through the mist released by cooling towers. It can be fatal but is treatable with antibiotics when caught early, health officials said.

The Health Department has ordered 76 buildings in the affected area to clean and disinfect their cooling towers, and all have confirmed they completed the work, the agency said. The Guggheinheim Museum and Metropolitan Museum of Art were among the buildings with cooling systems that tested positive for the bacteria.

Investigators are still working to identify the source of the outbreak.

Martin urged anyone who lives in or recently visited the neighborhood and has flu-like symptoms such as fever, chills, muscle aches or a cough to seek medical care immediately.

City Council Speaker Julie Menin, who represents the Upper East Side, called the death "heartbreaking" and said the person's loved ones were in her thoughts.

"As this outbreak continues to impact our community, we must remain focused on the health and safety of our neighbors," she said.