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Infectious diarrhoea is common and a very important cause of
morbidity and mortality in children under 5 years worldwide. The
gut is protected by gastric acid, bile salts, the mucosal immune
system and inhibitory substances that are produced by the normal
Organisms are transmitted by hands and fomites (faecal-oral
route), by food or water. The infective dose can be as few as 10
). Some foods (e.g. milk) or drugs (e.g. H2
antagonists and proton pump inhibitors) may reduce the protective
effects of gastric acid.
Bacteria enter the food chain from infected animals, from poor
hygiene during slaughter, and during butchering. Hens that are
chronically colonized with Salmonella
may produce eggs that are
contaminated. Improper cooking and storage may allow the multiplication
of bacteria (see below). Transmission is favoured by poor
sanitation; infection can spread rapidly causing significant mortality.
Cholera is capable of spreading worldwide (a pandemic).
Travellers' diarrhoea usually develops within 72 h of arrival in
a new country; Latin America, Africa and Asia are the regions
with the highest risks.
Patients pass two to four watery bowel
motions daily; blood and mucus are typically absent. The major
organisms implicated are enterotoxigenic Escherichia coli
and enteroadherent E. coli
(EAEC; see Pathogenicity of enteric Gram-negative bacteria
). Treatment is
with fluid replacement and antibiotics, including co-trimoxazole
- Toxin-mediated dysregulation of intestinal cells causing fluid
- Invasion of the intestinal wall occurs with destruction of the cells
- Secretory diarrhoea produces infrequent large-volume stools as
the absorptive capacity of the colon is overwhelmed.
- In dysenteric illness (e.g. Shigella), colonic inflammation
causes a loss in bowel capacity and frequent, often blood-stained
- Enterohaemorrhagic E. coli (EHEC) produce Shiga toxin (Stx),
which causes bloody diarrhoea and the haemolytic uraemic syndrome
(HUS), which is commonest with serotype O157:H7.
- There may be many small stools (typical of large-bowel infection)
or infrequent large stools (small-intestinal infection). Stools
may be blood stained when there is destruction of the intestinal
mucosa, or have a fatty consistency and offensive smell if malabsorption
- Dehydration and electrolyte imbalance may develop rapidly
with potentially fatal results, especially in cholera. Crampy
abdominal pain may accompany diarrhoea (e.g. Campylobacter
and Shigella infections); this may mimic acute abdominal conditions,
such as appendicitis.
- Fever is not always present.
- Septicaemia can occur in salmonellosis, but is rare in other diarrhoeal
- Secondary lactose intolerance, which is caused by loss of intestinal
lactase, may persist for a few weeks.
- Patients with IgA deficiency may have difficulty eradicating
Giardia; those with T-cell deficiency are prone to Salmonella and
Cryptosporidium (see Infections in immunocompromised patients
- Diagnosis is by culture using a range of media specific to different
groups of pathogens.
- Multiplex nucleic acid amplification tests (NAATs) are being
introduced into routine practice.
- Organisms should be typed using molecular methods for epidemiological
purposes (see Structure and classification of bacteria).
- Toxin may be detected in stool samples (e.g. Clostridium difficile
The management of diarrhoeal disease is based on adequate fluid
replacement and correction of electrolyte imbalances. Despite the
high outflow found in secretory diarrhoea, fluid absorption still
occurs. Oral rehydration solutions that consist of 150-155 mmol/L
sodium and 200-220 mmol/L glucose can be life-saving. Intravenous
fluid replacement is rarely necessary. Antimotility drugs are
of no benefit and may be dangerous, especially in small children.
Oral antibiotics, such as tetracycline or ciprofloxacin, which
shorten the duration of symptoms, may be of benefit in cholera
and other cases of severe fluid diarrhoea. Patients with severe
dysentery and salmonellosis should be treated with ciprofloxacin
or co-trimoxazole. Renal failure due to HUS following E. coli
O157 requires specialist management.
- Good sanitation is essential in preventing diarrhoeal disease.
- Animal husbandry and slaughter methods should be designed to
prevent the introduction of animal intestinal pathogens into the
human food chain.
- Food must be cooked to a sufficiently high temperature to kill
pathogens and, if not eaten immediately, refrigerated at a low
enough temperature to prevent any bacteria multiplying.
- Cooked food should be physically separated from uncooked
food to prevent cross-contamination. This is especially true in
institutional cooking (e.g. hospitals and restaurants), where many
individuals might become infected following a single failure of
- Travellers' diarrhoea can be reduced by careful choice of food
- Oral, heat-killed and live attenuated cholera vaccines are licensed
for use but the protection they provide is short-lived.
- Whole-cell vaccines, purified Vi polysaccharide vaccine and oral
Ty21a vaccine are available against typhoid. New Vi conjugate
vaccines are being developed.