Pont St. Esprit is a small town in southern France. In 1951 it became famous as the site of one of the most mysterious medical outbreaks of modern times.
As Dr's Gabbai, Lisbonne and Pourquier wrote to the British Medical Journal, 15 days after the "incident":
The first symptoms appeared after a latent period of 6 to 48 hours. In this first phase, the symptoms were generalized, and consisted in a depressive state with anguish and slight agitation.
After some hours the symptoms became more clearly defined, and most of the patients presented with digestive disturbances... Disturbances of the autonomic nervous system accompanied the digestive disorders-gusts of warmth, followed by the impression of "cold waves", with intense sweating crises. We also noted frequent excessive salivation.
The patients were pale and often showed a regular bradycardia (40 to 50 beats a minute), with weakness of the pulse. The heart sounds were rather muffled; the extremities were cold... Thereafter a constant symptom appeared - insomnia lasting several days... A state of giddiness persisted, accompanied by abundant sweating and a disagreeable odour. The special odour struck the patient and his attendants.In most patients, these symptoms, including the total insomnia, persisted for several days. In some of the patients, these symptoms progressed to full-blown psychosis:
Logorrhoea [speaking a lot], psychomotor agitation, and absolute insomnia always presaged the appearance of mental disorders. Towards evening visual hallucinations appeared, recalling those of alcoholism. The particular themes were visions of animals and of flames. All these visions were fleeting and variable.
In many of the patients they were followed by dreamy delirium. The delirium seemed to be systematized, with animal hallucinations and self-accusation, and it was sometimes mystical or macabre. In some cases terrifying visions were followed by fugues, and two patients even threw themselves out of windows... Every attempt at restraint increased the agitation.
In severe cases muscular spasms appeared, recalling those of tetanus, but seeming to be less sustained and less painful... The duration of these periods of delirium was very varied. They lasted several hours in some patients, in others they still persist.
In total, about 150 people suffered some symptoms. About 25 severe cases developed the "delirium". 4 people died "in muscular spasm and in a state of cardiovascular collapse"; three of these were old and in poor health, but one was a healthy 25-year-old man.
At first, the cause was assumed to be ergotism - poisoning caused by chemicals produced by a fungus which can infect grain crops. Contaminated bread was, therefore, thought to be responsible. Ergotism produces symptoms similar to those reported at Pont St. Esprit, including hallucinations, because some of the toxins are chemically related to LSD.
However, there have been other theories. Some (including Albert Hofmann, the inventor of LSD) attribute the poisoning to pesticides containing mercury, or to the flour bleaching agent nitrogen trichloride.
More recently, journalist Hank Albarelli claimed that it was in fact a CIA experiment to test out the effects of LSD as a chemical weapon, though this is disputed. What really happened is, in other words, still a mystery.
Link: The Crazies (2010) is a movie about a remarkably similar outbreak of mass insanity in a small town.
GABBAI, LISBONNE, & POURQUIER (1951). Ergot poisoning at Pont St. Esprit. British medical journal, 2 (4732), 650-1 PMID: 14869677