Gastroenteritis is caused by a wide range of pathogens including viruses, bacteria and parasites (as shown in Table 7.12.1). In developed countries, the majority of episodes are due to viruses, with rotavirus being by far the most common pathogen. The most common bacterial causes are Salmonella and Campylobacter. Shigella, Yersinia and Escherichia coli are less common, while Vibrio cholerae is seen in developing countries. Parasites such as Giardia and Cryptosporidium are sometimes the infective agent.

Viruses Bacteria Parasites Rotavirus Salmonella Cryptosporidium Norwalk virus Campylobacter jejuni Giardia lamblia Enteric adenovirus Shigella Entamoeba histolytica Escherichia coli Yersinia enterocolitica Vibrio cholerae

In general a bacterium is more likely to be the causative agent if:

There is blood or mucus in the stool.

There is significant abdominal pain.

There is a high-grade fever.

These infective agents cause gastroenteritis by one, or more mechanisms. Some directly invade the bowel wall, e.g. Salmonella or Shigella, some produce toxins prior to ingestion, e.g. Staphylococcus aureus, and some multiply and produce toxins within the gastrointestinal tract, e.g. Shigella.

In an uncomplicated acute bout of gastroenteritis, determining the causative pathogen is usually unnecessary, as this usually does not alter the management.

History

Most children with acute gastroenteritis present with a history of diarrhoea and vomiting. Abdominal pain and fever are sometimes accompanying symptoms. It is important to ask for specific details about these symptoms, to increase the certainty of the diagnosis of gastroenteritis and also to help assess the risk of dehydration in the child.

Diarrhoea refers to loose or liquid stools. The frequency, volume (small to voluminous) and consistency (semisolid to watery) and the presence of blood or mucus are all important. Similarly, the frequency and nature (bilious or non-bilious) of the vomiting are also important. The words ‘my child is vomiting everything he tries to drink’ can be used by parents to describe a child who has had either two or 20 vomits in the last 24 hours. It is important, therefore, to be specific in questioning.

The abdominal pain that can be associated with gastroenteritis is crampy in nature and commonly more pronounced in bacterial gastroenteritis. It is not accompanied by focal or significant findings on abdominal examination. If fever is a symptom, the height of the fever can be helpful. Although children with rotaviral gastroenteritis are often febrile, it is not usually high-grade. Such fevers are more likely in bacterial gastroenteritis or in other diagnoses altogether.

Specific details about the amount of fluid tolerated by the child are vital in assessing the risk of dehydration. Parents are usually able to estimate whether, over a 24-hour period, the child has taken one-quarter, one-half or three-quarters of normal intake. Intake that is consistently less than half of normal is of concern.

Specific questions about urine output (i.e. heaviness and frequency of wet nappies) are also important. Fewer than four wet nappies in 24 hours is of concern when assessing hydration status.

Questions about the level of alertness and activity of the child are also important. Lethargy may simply be an indication of significant dehydration in a child. However, more severe lethargy and drowsiness (particularly if out of proportion to that expected for the dehydration) may indicate another more serious diagnosis as the cause of the child’s symptoms, such as enteroviral meningitis.

Examination

The aim of the clinical examination is to exclude signs of an alternative cause of the symptoms, other than gastroenteritis (see Chapter 7.8) and to assess the degree of dehydration.

Occasionally pathogens causing gastroenteritis can cause extraintestinal disease. This can occur particularly with Shigella and Salmonella. Shigella can cause central nervous system irritation, which can manifest as encephalopathy or seizures. This may occur prior to the onset of diarrhoea. Salmonella can cause a bacteraemia, which can lead to focal infections including osteomyelitis and meningitis. The infant under 6 months of age is particularly at risk.

Assessment of dehydration

The accurate assessment of dehydration is difficult. Studies have shown that medical personnel tend to overestimate the degree of dehydration.² The gold standard in assessment of dehydration is a loss of weight compared with a recent pre-illness weight. For example, a 1-year-old weighing 10 kg a week ago who presents with gastroenteritis for 3 days and now weighs 9.5 kg, is approximately 5% dehydrated. However, a recent weight is rarely available in the ED. Therefore, tables such as Table 7.12.2 use a combination of clinical symptoms and signs to estimate the degree of dehydration.

It is important to remember that some of the signs and symptoms of dehydration can be affected by other factors. Mouth breathers have dry mucous membranes. Watery diarrhoea can make it difficult to assess if the child has a wet nappy from urine output. Crying can cause a sunken fontanelle to appear full. Tachycardia may be caused by a crying, anxious or febrile child; therefore it is the context and trend of the pulse that is important.

Various studies have attempted to validate combinations of these signs and symptoms with varying degrees of standardisation and scientific validity.²^–⁵ Difficulties arise as some of the signs are subjective and gold standards differ.

Gorelick et al ⁵ performed a good study in Philadelphia in 1997, which looked at the 10 clinical signs shown in Table 7.12.3. Using a gold standard of serial weight gain, they found that <3 signs correlated with <5% dehydration, 3–6 signs correlated with 5–9% dehydration and >7 signs correlated with >10% dehydration.