Traveller's diarrhoea (sometimes called 'Dehli belly') is diarrhoea that develops during, or shortly after, travel abroad. Diarrhoea is defined as 'loose or watery stools (faeces), usually at least three times in 24 hours'. Traveller's diarrhoea is caused by eating food, or drinking water, containing certain germs (microbes) or their poisons (toxins). The types of germs which may be the cause include:

1. Bacteria: are the most common microbes that cause traveller's diarrhoea. Common types of bacteria involved are:
2. Escherichia coli
3. Campylobacter Salmonella Shigella

Viruses: are the next most common, particularly norovirus and rotavirus.
Parasites: are less common causes. Giardia, cryptosporidium and Entamoeba histolytica are examples of parasites that may cause traveller's diarrhoea.

Often the exact cause of traveller's diarrhoea is not found and studies have shown that in many people, no specific microbe is identified despite testing (for example, of a stool (faeces) specimen).