I also had an upset tum on holiday, but used immodium( Superdrugs own version as cheeper) and felt much better. I think its prob due to drinking more (usually tea total at home) and eating foods your tummy is not used too rater than any food poison
Having said that, im always careful on holiday, checking food is hot and cooked through and if I chose salad at the hotel, I always took from underneath the dish, as its kept cooler and no flies have been on it.
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and I avoided street food etc. Thats all you can do, have a great holiday.