Nearly four dozen people have gotten sick amid what the Health Department has described as an "unusual" spike in Legionnaires' disease in the Bronx, officials said Thursday, adding 15 cases to the total authorities gave a day earlier in announcing the deadly outbreak.

Forty-six cases of the disease, a severe, often lethal, form of pneumonia spread through the air, have been reported in the south Bronx since July 10, city officials said Thursday. Two of the 46 patients, a man and a woman in their 50s, have died from the illness; authorities say they had other lung problems as well as Legionnaires'. Their identities have not been released.

The cases have been reported primarily in High Bridge, Morrisania, Hunts Point and Mott Haven, since July 10, the Health Department said.

Legionnaires' disease is caused by exposure to the bacteria Legionella; in most cases, people are exposed to the bacteria by inhaling contaminated aerosols from cooling towers, hot tubs, showers and faucets or drinking water.

Since the cases are widely dispersed — as in they're not clustered in one or two buildings —authorities do not believe the outbreak is connected to any contaminated drinking water, Health Commissioner Mary Bassett said at a news briefing Thursday.

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"The water supply in the south Bronx remains entirely safe. We don't know the source of this outbreak, but in recent months we have seen outbreaks associated with cooling towers and that's why we're focusing on them," Bassett said. "We're testing every cooling tower we can find in the area."

Twenty rooftop cooling towers, which are primarily on commercial buildings, have been tested so far; another 10 were tested Thursday, authorities said, and results were expected within a day.

Mayor de Blasio said that thus far, two rooftop cooling towers in the area had been found to be contaminated, including one at Lincoln Hospital and one at a private housing facility. Both are now being disinfected; the decontamination will be completed by Friday afternoon, authorities said.

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De Blasio and Bassett said there has been no evidence of contamination within Lincoln Hospital, and though the hospital has confirmed it is treating patients with the disease, Bassett said no one -- neither patients nor employees -- contracted it at the facility.

Both officials stressed there was no concern for alarm.

"People have to understand that this is a disease that can be treated -- and can be treated well if caught early," de Blasio said. "The exception can be with folks who are already unfortunately suffering from health challenges, particularly immune system challenges. But for the vast majority of New Yorkers, if they were even exposed, this can be addressed very well and very quickly so long as they seek medical treatment."

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Legionnaires' disease usually sets in two to 10 days after exposure to the bacteria and has symptoms similar to pneumonia, including shortness of breath, high fever, chills and chest pains. People with Legionnaires' also experience appetite loss, confusion, fatigue and muscle aches.

It cannot be spread person-to-person and those at highest risk for contracting the illness include the elderly, cigarette smokers, people with chronic lung or immune system disease and those receiving immunosuppressive drugs. Most cases can be treated successfully with antibiotics.

The Health Department urges anyone with symptoms to seek immediate medical attention.

"We are concerned about this unusual increase in Legionnaires' disease cases in the south Bronx," Bassett said Wednesday. "We are conducting a swift investigation to determine the source of the outbreak and prevent future cases."

Health Commissioner Mary Bassett and Mayor de Blasio address concerns about the Legionnaires’ outbreak in the Bronx that has sickened at least 31 people so far this month. Two people have died.

James Rouse, 42, died of Legionnaires' three months ago; he's not one of the two deaths linked to the more recent Bronx outbreak, but his family wonders if it's connected. He lived in Manhattan but taught music to children in the South Bronx. On April 30, he went to the hospital with a 104-degree fever, was diagnosed with Legionnaires' and then died 10 days later.

"If it turns out those two people died and it's related to my brother's death, and something could have been done about it — that kind of tragedy, I couldn't put into words," said brother John Rouse of Coram.

An outbreak last hit the Bronx in December. Between then and January, 12 people in Co-op City contracted the potentially deadly disease. Officials said a contaminated cooling tower was likely linked to at least 75 percent of those cases. No one died in that outbreak.

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