There has been a fourth death from a Legionnaires' disease outbreak in New York City. 

The NYC Department of Health said there are 99 confirmed cases, with 17 people currently hospitalized, as of Thursday. New cases have started to decline, officials said. 

Legionnaires' disease is a potentially deadly form of pneumonia, official say. The Legionella bacteria grows in warm, stagnant water and spreads through mist in the air. There is no person-to-person transmission. 

Symptoms can resemble the flu, including cough, fever, chills, muscle aches and shortness of breath. It can take up to two weeks for symptoms to show up. People over 50 and smokers are at greater risk. 

"I'm just telling my Harlemites this situation is under control"  

The NYC Legionnaires' cases have been clustered around five Central Harlem zip codes: 10027, 10030, 10035, 10037 and 10039. The outbreak has been traced to 12 cooling towers, including four city-run buildings, like Harlem Hospital, officials said.

Eleven of the 12 towers have undergone remediation, and the final one is expected to be completed Friday.

"I want to reassure everyone the air is safe to breathe and there is no risk to our drinking water or our water supply," Mayor Eric Adams said. "I'm just telling my Harlemites this situation is under control."

Adams then drank a cup of water during the news conference.

Medical experts and Public Advocate Jumaane Williams held an information session for Harlem residents on Thursday night.

"I'm more concerned that we've seen a drop in testing before this outbreak happened. I want to know what we're going to do to try and change that," Williams said.

Karen Diggs lives right across from Harlem Hospital.

"This just helped to calm my anxiety about the thing overall," Diggs said.

Officials have been urging residents in the area with flu-like symptoms to see their health care provider and not just assume it's a cold. 

12 Harlem cooling towers under scrutiny

Officials said they traced the outbreak back to a dozen cooling towers tested positive for the Legionnella bacteria. 

The towers are located, in part, at a number of city-owned buildings:

• BRP Companies, Lafayette Development LLC, 2239 Adam Clayton Powell Jr Blvd Manhattan, NY 10037   
• BVK, 215 W 125th St Manhattan, NY 10027 
• Commonwealth Local Development, 301 West 124th St, Manhattan, NY 10035  
• CUNY – City College Marshak Science Building, 181 Convent Ave, Manhattan, NY 10031  
• Harlem Center Condo, 317 Lenox Ave, Manhattan, NY 10030  
• NYC Economic Development Corporation, 40 West 137th St, Manhattan, NY 10037  
• NYC Health Department Central Harlem Sexual Health Clinic, 2238 5th Ave, Manhattan, NY 10030  
• NYC Health + Hospitals/Harlem, 506 Lenox Ave, Manhattan, NY 10037   
• The New York Hotel Trades Council Harlem Health Center,133 Morningside Ave, Manhattan, NY 10027 
• Wharton Properties, 100 W 125th St Manhattan, NY 10027 (3 of 8 towers) 

"Our investigation, hopefully, in the next few weeks will allow us to finally identify a connection between the patients who've gotten sick and the cooling tower that caused this. Eventually, what we will be able to potentially find out is the specific DNA test that will allow us to match which building and to which patient led to this cluster of cases," Acting Health Commissioner Dr. Michelle Morse said.

The infected towers have been given antibacterial treatments to help stop the spread of the Legionella bacteria at the root of the outbreak. 

City officials have since proposed stricter rules regarding cooling towers to boost testing and reporting requirements, and have imposed penalties for those who don't comply. 

Adams did not speak to whether inspection issues caused the outbreak.