A fifth person has died in New York City’s Legionnaires’ disease outbreak, health officials said Tuesday, as investigators continue searching for the source of an infection that has sickened at least 72 people over the past month.

The city’s Health Department has found Legionella bacteria in 34 cooling towers across 33 buildings, all of which have been cleaned. But officials still have not identified the source of the outbreak.

There is one encouraging sign: No new patients have reported symptoms in the past 10 days, according to the department.

Eight people remain hospitalized, while 56 have been discharged after treatment in the outbreak centered on Manhattan’s Upper East Side.

Legionnaires’ disease is a severe form of pneumonia caused by Legionella bacteria, which thrive in warm water and spread through contaminated water droplets from sources such as cooling towers and hot tubs. It does not spread from person to person and is treatable, but kills about 1 in 10 patients, according to the U.S. Centers for Disease Control and Prevention.

Health officials are cleaning and disinfecting 82 cooling towers at 80 buildings after inspections detected Legionella in systems at luxury apartment buildings, private schools and major museums in the affluent neighborhood. The findings come despite tougher testing rules introduced this spring and increased funding to expand inspections.

Some property owners whose cooling towers tested positive said they had acted quickly to address any risk. The Guggenheim Museum said an outside contractor tests and treats its cooling tower every month.

Jory Lange, a Texas attorney representing at least three patients in the current outbreak, said he also represents more than 50 people affected by last year’s Harlem outbreak, which killed seven people and sickened more than 100.

“There’s no excuse for this to keep happening,” Lange said. “New York already has the best and strongest regulations … and yet this still keeps happening.”

Health Commissioner Dr. Alister F. Martin said the department’s rapid response after the first confirmed cases “saved lives” and said investigators will use what they learn from the outbreak to strengthen future prevention efforts.

After last year’s Harlem outbreak, city leaders approved the hiring of 23 additional Legionella specialists. The department currently has 35 on staff, with 14 more in training and seven positions still to be filled.

The Health Department said it carried out nearly 1,600 cooling tower inspections during the first six months of the year, a 35% increase from the same period a year earlier.