A fourth person died during the weekend in a growing Legionnaires’ disease outbreak in the South Bronx, and city officials said the number of cases is likely to rise because of the bacterial infection’s incubation period. 

Since July 10, 71 people have contracted the disease, including the four who have died. Of the 55 who were hospitalized, 25 have been discharged, according to the city’s Department of Health and Mental Hygiene.

Officials said the four people who died were older adults with “underlying medical problems.” The disease causes pneumonia-like symptoms including fever, cough, chills and muscle aches. It can’t be transmitted from person to person.

The disease can spread through hot-water systems or cooling towers for air-conditioning units, said Stephen S. Morse, an epidemiology professor at Columbia University’s Mailman School of Public Health.

The towers emit a mist that can carry the Legionella bacteria through the air and can infect people who breathe it on the street below, said Jay Varma, the health department’s deputy commissioner of disease control.

Older people, smokers and people with lung conditions are particularly susceptible to Legionnaires’ disease, Mr. Morse said. “In the vast majority of cases, if treated promptly, it can be managed, even in people who are elderly or infirm,” he said.

Click for more from The Wall Street Journal.