What was the cause of Pont-Saint-Esprit mass poisoning in 1951, during which "the city went mad"?

The 1951 Pont-Saint-Esprit mass poisoning occurred in the small town of Pont-Saint-Esprit in southern France. More than 250 people suffered hallucinations and other nervous system disturbances, leading to 50 persons being interned in asylums and 7 deaths. A foodborne illness was suspected, and among these it was originally believed to be a case of "cursed bread". Most academic sources accept ergot poisoning as the cause of the epidemic.