Flies can spread disease from excrement to uncovered food. Viruses or toxins can be present in shellfish, which filter pollutants coming from sewerage outlets. Risk of transmission depends on local public health systems, how food and drink is prepared, and environmental hygiene. Factors affecting incidence Local incidence rates range from 20 to 80 per cent and are determined by the prevalence of endemic disease, climate, and public health infrastructure. In addition, the number of flies increases at warmer times of the year, resulting in increased transmission and more episodes of diarrhoea.
Young travellers tend to be less cautious and are more likely to get travellers' diarrhoea.
Clinical features Travellers' diarrhoea is defined as the passing of three or more loose stools in 24 hours, associated with nausea, cramp and bloody or mucous stools. It usually lasts for three to five days and subsides without treatment. About 20 per cent of travellers will be confined to bed, and 10-20 per cent will develop more serious symptoms of fever or blood in the stools, which suggests invasive disease. Up to 10 per cent will have symptoms for over a week. It can have serious consequences for vulnerable travellers such as the elderly or young children.