large coorporation fast food chains, IMO, has pretty controlled personel and routines and i highly doubt that McD or Burger King would serve you something bad regarding their meat. and from what i've gathered meat is the usual culprit if you get poisoning from food.
and i believe it onsets a couple of hours later at least, not directly after consumption.
i had food poisoning two times in two months this year. it was hell, especially the second time where i dehydrated to a degree where very many muscles started cramping up.
if you get this shit, try to drink all the time. water water water.