Gastroenteritis - Clinical Tree

Essentials

1
Gastroenteritis is usually a benign, self-limiting disease that can be diagnosed clinically, warrants no specific investigation and settles spontaneously with symptomatic treatment and oral fluid therapy.
2
The cardinal clinical feature of gastroenteritis is diarrhoea, which may be accompanied by varying degrees of nausea and vomiting, abdominal cramping and pain, lethargy and fever.
3
The clinical examination is directed at confirming the diagnosis of gastroenteritis, excluding alternative diagnoses and determining the degree of dehydration.
4
A wide variety of viruses, bacteria and protozoa may cause gastroenteritis. In developed countries, common viral agents include rotavirus and norovirus. Common bacteria include Campylobacter jejuni, Staphylococcus aureus, Escherichia coli, Shigella dysenteriae and Salmonella enteriditis. Common protozoa include Giardia lamblia.
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The principles of treatment of gastroenteritis are to replace the fluid losses orally or intravenously, minimize the patient’s symptoms by the use of antiemetic therapy and, in some circumstances, administer specific antimicrobial agents.
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Introduction of rotavirus vaccine in Australia in 2007 has led to the reduction of both rotavirus and non-rotavirus gastroenteritis.

Introduction

Gastroenteritis is a common clinical syndrome. It poses one of the world’s major clinical and public health problems and, in developing countries with poor-quality drinking water and low levels of sanitation, it is a major cause of morbidity and mortality, especially among children and the elderly.

Gastroenteritis is caused by infection of the gastrointestinal tract by various viruses, bacteria and protozoa. Transmission is most commonly by the faecal-oral route. The syndrome consists of diarrhoea, abdominal cramping or pain, nausea and vomiting, lethargy, malaise and fever. Each of these features may be present to a varying degree and may last from 1 day to more than 3 weeks.

In developed countries, even though serious morbidity and mortality are low, gastroenteritis may be an extremely painful and unpleasant event, causing disruption to daily life and significant loss of work and school days. Patients often seek emergency medical care because of the acuteness of onset of symptoms, the frequency of the diarrhoea, the severity of abdominal pain and cramps or because of concerns regarding dehydration.

Pathogenesis and pathology

Microorganisms of all descriptions are constantly entering the gastrointestinal tract through the mouth. Extremely few of these progress to cause clinical illness. The natural defences of the gastrointestinal tract against infection include gastric acid secretion, normal bowel flora, bile salt production, bowel motility, mucosal lymphoid tissue and secreted immunoglobulin A. People with disturbances in any of these defences are more prone to develop a clinical infection. For example, patients with achlorhydria, bowel stasis or blind loops, immunodeficiency states or recent antibiotic therapy that has disturbed bowel flora are prone to develop gastroenteritis. Some organisms, such as rotavirus, occur principally in children, as previous infection confers immunity.

Microbiology

A wide variety of viruses, bacteria and protozoa may cause gastroenteritis, and the list is continually growing. Viral agents include rotavirus, enteric adenovirus, astrovirus, calicivirus, norovirus, coronavirus and cytomegalovirus. Bacteria include C. jejuni , S. aureus , Bacillus cereus , E. coli , Vibrio cholerae , S. dysenteriae , S. enteriditis , Yersinia enterocolitica , Clostridium perfringens and C. difficile . Protozoa include G. lamblia , Cryptosporidium parvum and Entamoeba histolytica .

Micro-organisms cause gastroenteritis by a number of mechanisms. They may release preformed toxins prior to ingestion, multiply and produce toxins within the gastrointestinal lumen, directly invade the bowel wall or use a combination of toxins and invasion.

S. aureus and B. cereus produce a variety of toxins in stored food that are subsequently ingested. These toxins are absorbed and, within hours, act on the central nervous system to produce an illness characterized predominantly by vomiting and mild diarrhoea.

Invasive bacteria are characterized by Salmonella , which invades the mucosa (primarily of the distal ileum) producing cell damage and excessive secretion. Shigella likewise invades the mucosa but also produces toxins that have cytotoxic, neurotoxic and enterotoxic effects.

The many strains of E. coli have been divided into five groups, depending on the pathology of the diseases they cause. These are enteropathogenic, enterotoxigenic, enteroinvasive, enteroaggregative and enterohaemorrhagic. Enterohaemorrhagic E. coli is associated with haemorrhagic colitis and the haemolytic-uraemic syndrome, whereas enterotoxigenic E. coli is associated with traveller’s diarrhoea. The protozoan G. lamblia adheres to the jejunum and upper ileum, causing mucosal inflammation, inhibition of disaccharidase activity and overgrowth of luminal bacteria.

Rotavirus is estimated to be the cause of 50% of gastroenteritis admissions in Australia prior to the introduction of rotavirus vaccine. Rotavirus vaccine was introduced into the funded Australian National Immunization Programme in July 2007. A comparison study of gastroenteritis prior to the vaccine’s introduction against the 30 months following it showed a marked reduction in emergency department (ED) encounters as well as hospitalization for rotavirus and non-rotavirus gastroenteritis. There also appears to be an indirect population-protective effect of the vaccine as older children who were ineligible for the rotavirus vaccine have also demonstrated reduced hospitalization and positive rotavirus tests.

Epidemiology

In Australia the estimated incidence of gastroenteritis is 17.2 million cases per year. Thirty-two percent of these cases are food-borne, which is equivalent to 0.3 episodes per person per year. Altogether, food-borne gastroenteritis causes 15,000 hospitalizations and 80 deaths annually. The economic impact on the health care system is estimated at $30 million per year.

Norovirus, enteropathogenic E. coli , Campylobacter and Salmonella are the leading causes of gastroenteritis in Australia, with norovirus considered to be the leading cause worldwide. Norovirus outbreaks are commonly reported in aged-care facilitates, health care facilities and child care centres, causing immense disruption to the systems meant to be looking after this vulnerable populations.

Gastroenteritis may occur in many settings. It may be a sporadic isolated event; a small outbreak either within a family or other close living group, such as in a geriatric residential facility; or part of a larger community epidemic. It may occur in travellers, either while still overseas or on their return home. It is important to be aware of the circumstances and context in which the illness occurs, as these will often dictate the course of investigation or management.

Clinical features

History

The clinical history and examination are directed at confirming the diagnosis of gastroenteritis, excluding other diagnoses and determining the degree of dehydration.

The principal clinical manifestation of gastroenteritis is diarrhoea. There is a lack of standardized definition of gastroenteritis. The World Health Organization syndromic definition of gastroenteritis is ‘three or more abnormally loose or fluid stools over 24 hours’. The diarrhoea of gastroenteritis is often watery and profuse in the early stages of the illness and may last for up to 3 weeks. It is important to determine the frequency, volume and characteristics of the stool. Some organisms—such as enterohaemorrhagic E. coli , Shigella , Salmonella , Campylobacter and Entamoeba histolytica —may cause acute and bloody diarrhoea, whereas others, such as Giardia , may cause loose, pale, greasy stools.

Abdominal pain is common and is most often described as a diffuse intermittent colicky pain situated centrally in the abdomen. It may occur just prior to a bowel action and be relieved by that. Severe pain is often caused by Campylobacter , Yersinia and E. coli . Abdominal pain is also the hallmark of many other forms of intra- and extra-abdominal pathology. Diagnoses other than gastroenteritis should be seriously considered if the pain is well localized, constant and severe or if it radiates to the back or shoulder.

Vomiting may be present, particularly early in the illness, and can be variable in severity and persistence. The amount of vomiting and the ability to keep down clear fluids should be determined, as this will dictate the management of dehydration. Severe vomiting often occurs with organisms that produce preformed toxin, although it does not usually persist for longer than 24 hours. Anorexia, nausea and lethargy are common. Fever and systemic symptoms, such as headache, are prominent with organisms such as Yersinia , that invade the bowel wall and enter the systemic circulation. Lethargy may be related to the dehydration or merely the strain of constant and persistent diarrhoea from any aetiology.

Specific inquiry regarding fluid status is essential. The aim should be to determine the amount of fluids that have been taken orally and kept down over the course of the illness, along with the estimated urine output. It is also important to ascertain pre-existing or intercurrent illness, such as diabetes or immunosuppression, which may alter management.

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