Two words. Egg tacos. CNN is reporting more that 700 people attending a political rally in Mexico have come down with symptoms. No specific food item has been identified but one person indicated egg tacos. With the rapidity of the onset of symptoms, I am betting on Staph aureus food poisoning. Symptoms occur in as little as 30 minutes after consumption. However, if it is Salmonella, or Shigella, the infectious dose would have had to been huge in order to see symptoms in so many so quickly.
More as details emerge.