A fourth person has died in what the New York City Health Department is describing as an "unusual" spike in Legionnaires' disease in the Bronx, officials said Saturday. The news comes as two more Bronx buildings tested positive for the legionella bacteria.

A Verizon office building at 117 E. 167th St. is the fourth location to test positive, according to Verizon spokesman John Bonomo. Streamline Plastic Co. at 2590 Park Ave. is the fifth location to test positive. Remediation, removal of the contaminants, is complete at the Verizon location and has begun at the plastic company, officials said. Verizon said that it is performing checks on all cooling systems at all its facilities in the Bronx.

Seventy-one 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. That's 14 new cases since Friday, when 57 cases were announced. The four patients who died had underlying health conditions, authorities said.

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.

Twenty-two buildings have been visited as "disease detectives" hunt for the source of the outbreak, the city said Friday. Seventeen of those buildings have cooling towers -- three of those tested positive for Legionella, including one at Lincoln Hospital; one at Concourse Plaza, a shopping plaza; and one at the Opera House Hotel.

"Whatever's in the atmosphere gets pulled into the cooling tower, so there's a lot more dirt and debris and areas that organisms can grow in," Pete Stempkowski, of Clarity Water Technologies, said.

Lincoln Hospital was decontaminated this week; decontamination efforts at Concourse Plaza are ongoing; and the city said disinfection efforts began at the Opera House Hotel Friday. None of the 57 reported Legionnaires' patients stayed at the Opera House Hotel as guests.

"We're taking all the necessary steps to make sure the hotel is safe, that the hotel is still a safe place to stay and make sure that no one gets sick from this bacteria," the hotel's manager, Julio Vargas, said.

Mayor de Blasio and Health Commissioner Mary Bassett said at a briefing Thursday there was no evidence of contamination within Lincoln Hospital, and though the hospital confirmed it is treating patients with the disease, Bassett said no one -- neither patients nor employees -- contracted it at the facility.

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.

"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."

Authorities are awaiting the results for six of the 17 cooling towers tested.

Both de Blasio and Bassett 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 Thursday. "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."

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.

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.

Officials will hold a town hall discussion with health experts Monday at the Bronx Museum of the Arts at 6 p.m.