New York City's worst-ever Legionnaires' disease outbreak has now sickened 124 people, the de Blasio administration said Saturday.

The previous tally had been 121, although no new diagnoses have been made since Aug. 3. Reports of Legionnaires' cases often take several days reach the health department. The latest five cases, like the others, are clustered in the South Bronx.

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The flare-up of the bacterial pneumonia has killed 12 people since July 10.

Health officials say they suspect that the source of the flare-up -- one or more cooling towers containing the bacteria -- has been successfully disinfected.

The disease is so named because it was discovered after an outbreak at an American Legion meeting in 1976 in Philadelphia. It's transmitted through air-conditioning, showers, baths, cooling towers or other water sources. It cannot be transmitted between people.