28th July 2023

Gastrointestinal Infections

The most common manifestation of bacterial gastrointestinal infections is gastroenteritis, which typically presents with vomiting and diarrhoea (often bloody), associated with abdominal pain and variable systemic upset. The incubation period varies depending on the pathogen, but generally, symptoms present within 24-48 hours of exposure. Many infections are due to contaminated food, and these then spread rapidly person-to-person through faeco-oral spread.

More detail on this topic can be found in Bowel Infection and Inflammation.

Aetiology

The most common cause of gastroenteritis in the UK is Campylobacter species. They generally contaminate chicken, with poor food hygiene increasing the risk of infection. Barbecues are a common ‘exposure’ event, often seen in MRCP questions.

Salmonella food poisoning is another important cause of gastroenteritis. Cases have decreased after a successful vaccination campaign, but it may still cause outbreaks which are often related to specific venues with catered food, such as weddings. Salmonella species are an important cause of septic arthritis in sickle cell patients.

Typhoid, or enteric fever, is an important Salmonella complication, most associated with the typhi and paratyphi species. High fever, relative bradycardia and rose spots are classical findings.

Bacillus cereus is said to have a short incubation period of only a few hours and classically comes from reheating rice, with vomiting a key feature.

There are four species of Shigella – two endemic in the UK in S. sonnei and S flexneri, and two imported in S. bodyi and S. dysenteriae. The endemic forms may be spread by sexual contact, with prevalence high in men who have sex with men. Shigellosis outbreaks have also been described in nursery settings.

Escherichia coli O157:H7, sometimes called STEC (Shiga toxin-producing Escherichia coli), is associated with animal contact. A common case scenario is farms or petting zoos. Hemolytic uraemic syndrome (HUS) is an important complication. Generally seen in children, it causes nephrotic syndrome and is associated with anaemia and thrombocytopenia. Characteristic features are vomiting, bloody diarrhoea, fever, confusion, and purpura/petechiae.

Listeria monocytogenes can affect any individual, usually causing non-specific diarrhoea and vomiting. Soft cheese, unpasteurised milk, smoked meats, and unwashed produce have all been linked to the acquisition of Listeria. Risk factors for the disease include pregnancy, extremes of age, alcohol excess and immunodeficiency. Listeria also affects sheep, where it can cause spontaneous abortion, and farmers are hence at increased risk of the disease. It is important to be aware of especially in the context of pregnancy, as Listeria can cause meningitis in neonates. For this reason, pregnant women are advised to avoid high risk foods.

Management

Most cases of acute bacterial gastroenteritis are self-limiting and do not require antibiotics. Those at the extremes of age, with prolonged symptoms, or the immunocompromised may require treatment. Ciprofloxacin is a reasonable choice of antibiotic in most cases, although there are increasing reports of resistance in imported diseases such as Shigella. Azithromycin is another option.

Whilst gastroenteritis is usually caused by an exogenous microorganism, other gastrointestinal infections are often caused by displaced bacteria from the usual GI tract flora. This is seen in biliary tract infections, such as cholecystitis, cholangitis and liver abscesses, peritonitis, and bowel perforation. As such, these infections are usually polymicrobial, and organisms such as Escherichia coli Klebsiella pneumoniae, Enterococcus and anaerobes are often found on specimen cultures. An empirical combination of cefuroxime and metronidazole is used to treat suspected intra abdominal infection until sensitivities are available.

More information about other abdominal infections, such as those of the liver, gallbladder and pancreas, can be found in the Hepatic Pathology and Pancreatico-biliary Pathology sections.