I go HCMC often for 15 years. Only 1 time get diahorrea eating seafood in D4. That time my vietnamese friend didnt get diahorrea. Until today I dont know whether food is not clean or I ate too much proteins in a short time leading to diahorrea.Dining at restaurants present tremendous value as compared to sg. But there are those that chop carrot head also. I normally avoid roadside stalls unless it is michelin guide/recommended, lest I run the risk of diarrhea, to ensure my trip is not affected.
But overall just 1 time diahorrea in 15 years.