I am the last person to defend McDonald's but if you were ill with food poisoning only minutes after eating there, I can assure you it wasn't the french fries that made you sick.Although… on this trip I had no problems in Isaan where I eat food from local vendors but as soon as I went with Lisa to Nana Soi 4 Mc Donald’s few minutes after I got food poisoning from some outdated French fries.
I was told years ago that the way to determine what meal was the one that caused the illness, count back 8 hours from the first time you vomit. I have done it everytime since then whenever I got sick & I have found you can almost set your clock by it.
However if the french fries were contaminated with something, e.g. cleaning chemical, insecticide, etc, then they could have made you sick immediately. Could you taste anything odd? Or was there too much ketchup & mayo to tell?