What of other countries?
I don't know how blame could be placed on antibiotics as the "cause" for obesity in this continent (NAm). Looking for example at China, where antibiotics are given out or virtually every illness, everything from sniffles to the flu (I've spent a lot of time there, speak the language, have much experience with both in-country and ex-pat communities); if they were the key factor in obesity, than it would be at least as huge (no pun intended) an issue there as it is here. The main reason to cut back on over prescription of antibiotics is not weight gain, it's that we are creating super-bugs resistant to any medicine. I think China poses the biggest threat for this with its current medical system and the shear numbers of crowded cities.