July 28 (UPI) — A sixth person has died in the Upper East Side’s Legionnaires’ disease outbreak, New York City health officials said Tuesday, even as there has been no new cases diagnosed in nearly two weeks.

The identity of the deceased patient has not been released. Dr. Alister Martin, NYC’s health commissioner, said they were “heartbroken” to announce the death.

“We extend our heartfelt condolences to their loved ones and our thoughts are with them during this difficult time,” he said in a social media statement.

NYC health officials have been battling the outbreak since at least July 2, when the cluster was first made public after two people were diagnosed with the disease.

A total of 90 people have tested positive for Legionnaires’ disease in the outbreak affecting three ZIP codes on the Upper East Side, though no new cases hve been diagnosed since July 17. The last death was reported on July 21.

Of the diagnosed cases, six remain hospitalized, health officials said.

NYC health officials believe they have eliminated the source of the disease.

Legionnaires’ disease is caused by Legionella bacteria. Amid the outbreak, 183 cooling towers within the affected area were tested for Legionella bacteria. Officials said 77 of them tested PCR-positive for the bacteria, indicating its DNA was present, followed by 59 of them testing culture-positive, confirming the presence of live Legionella bacteria.

All towers that tested PRC-positive have since been cleaned and disinfected, according to the city, which ordered the maintenance to be conducted.

“We continue to believe the source of exposure has been eliminated,” Martin said Tuesday.

“At this time, no one has reported new symptoms in over two weeks; no one has been diagnosed in over 10 days,” he said.

Legionella bacteria grow in warm water. Those who inhale water vapor that contains the bacteria can get sick with Legionnaires’ disease, which is a form of pneumonia that causes flu-like symptoms. Most people exposed to the bacteria do not develop the disease. However, among those who do contract it, complications can be fatal.

According to the U.S. Centers for Disease Control and Prevention, between 8,000 and 18,000 people are hospitalized with Legionnaires’ disease each year in the United States.