37 Gastro-intestinal infections
Gastro-intestinal infections represent a major public health and clinical problem worldwide. Many species of bacteria, viruses and protozoa cause gastro-intestinal infection, resulting in two main clinical syndromes. Gastroenteritis is a non-invasive infection of the small or large bowel that manifests clinically as diarrhoea and vomiting. Other infections are invasive, causing systemic illness, often with few gastro-intestinal symptoms. Helicobacter pylori, and its association with gastritis, peptic ulceration and gastric carcinoma, is discussed in Chapter 12.
Epidemiology and aetiology
Gastro-intestinal infections can be transmitted by consumption of contaminated food or water or by direct faecal–oral spread. Air-borne spread of viruses that cause gastroenteritis also occurs. The most important causes of gastro-intestinal infection, and their usual modes of spread, are shown in Table 37.1. In developed countries, the majority of gastro-intestinal infections are food borne. Farm animals are often colonised by gastro-intestinal pathogens, especially Salmonella and Campylobacter. Therefore, raw foods such as poultry, meat, eggs and unpasteurised dairy products are commonly contaminated and must be thoroughly cooked to kill such organisms. Raw foods also represent a potential source of cross-contamination of other foods, through hands, surfaces or utensils that have been inadequately cleaned. Food handlers who are excreting pathogens in their faeces can also contaminate food. This is most likely when diarrhoea is present, but continued excretion of pathogens during convalescence also represents a risk. Food handlers are the usual source of Staphylococcus aureus food poisoning, where toxin-producing strains of S. aureus carried in the nose or on skin are transferred to foods. Bacterial food poisoning is often associated with inadequate cooking and/or prolonged storage of food at ambient temperature before consumption. Water-borne gastro-intestinal infection is primarily a problem in countries without a sanitary water supply or sewerage system, although outbreaks of water-borne cryptosporidiosis occur from time to time in the UK. Spread of pathogens such as Shigella or enteropathogenic Escherichia coli by the faecal–oral route is favoured by over-crowding and poor standards of personal hygiene. Such infections in developed countries are most common in children and can cause troublesome outbreaks in paediatric wards, nurseries and residential children’s homes.
Causative agent | Chief mode(s) of spread | Pathogenic mechanisms |
---|---|---|
Bacteria | ||
Campylobacter | Food, especially poultry, milk | Mucosal invasion |
Enterotoxin | ||
Salmonella enterica, non-typhoidal serovars | Food, especially poultry, eggs, meat | Mucosal invasion |
Enterotoxin | ||
Salmonella enterica serovars Typhi and Paratyphi | Food, water | Systemic invasion |
Shigella | Faecal–oral | Mucosal invasion |
Enterotoxin | ||
Escherichia coli | ||
Enteropathogenic | Faecal–oral | Mucosal adhesion |
Enterotoxigenic | Faecal–oral, water | Enterotoxin |
Enteroinvasive | Faecal–oral, food | Mucosal invasion |
Verotoxin-producing | Food, especially beef | Verotoxin |
Staphylococcus aureus | Food, especially meat, dairy produce | Emetic toxin |
Clostridium perfringens | Food, especially meat | Enterotoxin |
Bacillus cereus | ||
Short incubation period | Food, especially rice | Emetic toxin |
Long incubation period | Food, especially meat and vegetable dishes | Enterotoxin |
Vibrio cholerae O1, O139 | Water | Enterotoxin |
Vibrio parahaemolyticus | Seafoods | Mucosal invasion |
Enterotoxin | ||
Clostridium difficile | Faecal–oral (nosocomial) | Cytotoxin |
Enterotoxin | ||
Clostridium botulinum | Inadequately heat-treated canned/ preserved foods | Neurotoxin |
Protozoa | ||
Giardia lamblia | Water | Mucosal invasion |
Cryptosporidium | Water, animal contact | Mucosal invasion |
Entamoeba histolytica | Food, water | Mucosal invasion |
Viruses | Food, faecal–oral, respiratory secretions | Small intestinal mucosal damage |
Pathophysiology
Clinical manifestations
Many cases of gastro-intestinal infection are asymptomatic or cause subclinical illness. Gastroenteritis is the most common syndrome of gastro-intestinal infection, presenting with symptoms such as vomiting, diarrhoea and abdominal pain. The term ‘dysentery’ is sometimes applied to infections with Shigella (bacillary dysentery) and Entamoeba histolytica (amoebic dysentery), where severe colonic mucosal inflammation causes frequent diarrhoea with blood and pus. Table 37.2 shows the most important causative agents of gastroenteritis together with a brief description of the typical illness that each causes. However, the symptoms experienced by individuals infected with the same organism can differ considerably. This is important because it means that it is rarely possible to diagnose the cause of gastroenteritis on clinical grounds alone.
Causative agent | Incubation period | Symptoms (syndrome) |
---|---|---|
Campylobacter | 2–5 days | Bloody diarrhoea |
Abdominal pain | ||
Systemic upset | ||
Salmonella | 6–72 h | Diarrhoea and vomiting |
Fever; may be associated bacteraemia | ||
Shigella | 1–4 days | Diarrhoea, fever (bacillary dysentery) |
Escherichia coli | ||
Enteropathogenic | 12–72 h | Infantile diarrhoea |
Enterotoxigenic | 1–3 days | Traveller’s diarrhoea |
Enteroinvasive | 1–3 days | Similar to Shigella |
Verotoxin-producing | 1–3 days | Bloody diarrhoea (haemorrhagic colitis) |
Haemolytic uraemic syndrome | ||
Staphylococcus aureus | 4–8 h | Severe nausea and vomiting |
Clostridium perfringens | 6–24 h | Diarrhoea |
Bacillus cereus | ||
Short incubation period | 1–6 h | Vomiting |
Long incubation period | 6–18 h | Diarrhoea |
Vibrio cholerae O1, O139 | 1–5 days | Profuse diarrhoea (cholera) |
Vibrio parahaemolyticus | 12–48 h | Diarrhoea, abdominal pain |
Clostridium difficile | Usually occurs during/just after antibiotic therapy | Diarrhoea, abdominal pain, pseudomembranous enterocolitis |
Giardia lamblia | 1–2 weeks | Watery diarrhoea |
Cryptosporidium | 2 days–2 weeks | Watery diarrhoea |
Entamoeba histolytica | 2–4 weeks | Diarrhoea with blood and mucus (amoebic dysentery), liver abscess |
Viruses | 1–2 days | Vomiting, diarrhoea |
Systemic upset |
Enteric fever, resulting from infection with S. enterica