New York City health officials are tracking an outbreak of Legionnaires’ disease that has killed two people and sickened dozens of others in the South Bronx, Mayor Bill de Blasio’s administration said Wednesday.

The Department of Health and Mental Hygiene said 31 cases have been reported since July 10.

Most of the cases have been reported from the South Bronx neighborhoods of Highbridge, Morrisania, Hunts Point and Mott Haven, officials said.

“We are conducting a swift investigation to determine the source of the outbreak and prevent future cases,” said Mary Bassett, the health commissioner.

Dr. Bassett said officials are “concerned about this unusual increase” in cases in the South Bronx. She described the outbreak as an “evolving situation in which the numbers may change.”