To quote from a book about climbing Mount Everest, the author stated that the hardest challenge with mountaineering in Nepal is not getting sick in Kathmandu!But that doesn't mean that every trip to Nepal, India or the like will see you with the runs or throwing up; a normal healthy experience is quite possible with a bit of common sense and a fair size chunk of luck. So are all the cold salads, ice cubes in drinks, fruit juices, hand-made ice creams, raw food and buffet warnings.It goes without saying that the longer you are away the higher your chances of picking something up becomes although equally you will build up resistance over time. Bacteria and injected water can be inside melons, so many say it's best to avoid melons. Paranoia, for example about ice on hot days in popular tourist hot-spots really is unnecessary.
Chances are you will probably get some form of diarrhoea at some time during a long trip.
A distinction should be drawn between general travellers' diarrhoea, and severe diarrhoea.
The former which is more of an annoyance than a major problem, can normally be clocked up to changes in diet, time-zone, irregular eating and general stress.
Montezuma's revenge, the Delhi belly, worship to the porcelain god...
call it what you like, food poisoning and similar [vomiting] viral infections are an unfortunate caveat of travel and can strike at any time and in any place.