Epidemiology

Gastrointestinal tract infections are among the most commonly reported diseases worldwide, causing considerable morbidity and mortality. Although most prevalent in countries where sanitation and drinking water quality are poor, intestinal infections are common in the UK (Fig. 3.21.1). All parts of the gastrointestinal tract are susceptible to infection by a variety of microorganisms and, with the exception of certain nematodes that penetrate the skin, infection arises from ingestion:

directly from an infected human or animal by hand to mouth (faecal–oral)

indirectly from contaminated food or water

by consumption of food in which microbes have multiplied (food poisoning).

Fig. 3.21.1 Causes of diarrhoea in the UK in 2005. ETEC, enterotoxic Escherichia coli; VTEC, verotoxin-producing E. coli.

Although the gastrointestinal tract is vulnerable to infection, it is also well defended. The acidity of the stomach fluids (pH 2.0) is a barrier to most microbes and stops entry of pathogens into the intestinal tract. The small and large intestines are rich in commensal bacterial flora, which prevent pathogen colonization (the colon may contain 10¹² bacteria/g faeces). Secretory IgA and lymphoid tissue (Peyer’s patches) in the small intestine also provide immune protection.

Clinical features and management

Intestinal infections are diagnosed by the detection of organisms in faecal specimens using electron microscopy, immunoassay or gene detection for viruses, culture and biochemical identification of bacteria, and microscopy and immunoassays for protozoa and helminths.