Many different viruses cause gastroenteritis ( inflammation of stomach and intestines ), including rotaviruses - for which there IS a vaccine - and noroviruses - no vaccine but usually not serious, unless there are other health problems especially in the elderly, or infants. Viral gastroenteritis is often called " stomach flu " although it's not caused by the flu virus, and norovirus the " winter vomiting virus " because in this country there are more infections in winter.
The " 90 % " quoted by Wikipedia is misleading and guesswork - in most cases the diagnosis is clinical with no laboratory testing - indeed most people rapidly get better ( in a few days ) without seeing a doctor. However, the general rules for avoiding " norovirus " apply also to the many other types of gastoenteritis.
It's important to remember there are many causes of gastroenteritis apart from viruses. Traveller's diarrhoea may simply reflect change of diet and type of bugs living in the gut. More severe forms are usually associated with bacteria ( E.coli, Salmonella, Campylobacter, and Shigella ), a protozoan ( Giardia ) or Rotavirus. Mild, transient symptoms can be controlled with antimotility agents such as loperamide ; more severe, prolonged symptoms may require an antibiotic ( ciprofloxacin or metronidazole ). Antibiotics should NOT be taken prophylactically ( for " prevention " ) - they are prescription-only in the UK and readily available to buy in the Philippines.
Medical assistance is needed, wherever the symptoms occur, if the bowel motions are blood-stained, there is a fever, other symptoms like confusion, or the diarrhoea persists longer than 72 hours.
