Panic In the Streets (1950) by Elia Kazan with Richard Widmark

and starring Paul Douglas, Barbara Bel Geddes. Jack Palance, Zero Mostel
Shot exclusively on location in New Orleans, Louisiana and featuring numerous New Orleans citizens in speaking and non-speaking roles.
The film tells the story of Clinton Reed, an officer of the U.S. Public Health Service (played by Richard Widmark) and a police captain (Paul Douglas) who have only a day or two in which to prevent an epidemic of bubonic plague after Reed determines a waterfront homicide victim is an index case. Co-stars include Barbara Bel Geddes (as Reed's wife Nancy), Walter Jack Palance (in his film debut) and Zero Mostel — the latter two play associates of the victim who had prompted the investigation.