Mayor Bill de Blasio made a visit to the Bronx to talk to concerned residents about the rising death toll from Legionnaires' disease.

According to de Blasio, the number of reported cases is up to 86 since July 10, with seven deaths and 64 hospitalizations. However, he reassured New Yorkers not to panic, saying that those who have died had pre-existing medical conditions.

Health Commissioner Mary Basset says those underlying conditions could include chronic lung diseases such as asthma, emphysema or bronchitis. She says the number of cases is so high in the South Bronx because there is a higher underlying disease burden in the area, which is the poorest district in the continental U.S.

Health officials say they have traced the likely cause of the outbreak to cooling towers releasing mist contaminated with legionella bacteria, which causes Legionnaires' disease when inhaled. Five cooling towers tested positive for the bacteria, but all have since been decontaminated. The last tower was cleaned on Tuesday.

The mayor emphasizes the importance of seeking medical treatment immediately at the first sign of Legionnaires'. First-day symptoms include headache, fever, muscle pain and chills. Symptoms progress to cough, shortness of breath, chest pain, gastrointestinal symptoms and confusion or other mental changes. There is a 10-day incubation period for the symptoms to develop.

Legionnaires' can be treated with antibiotics. It cannot be spread from person to person.