Gastroenteritis is a general term which refers to an acute diarrhoeal illness characterised by loose or watery frequent motions, abdominal cramps and perhaps nausea or vomiting. It is usually food and water borne and thus often referred to as 'food poisoning'. It is often contracted during travel to countries where public hygiene and water quality are not as good as that in the home of the traveller and this is commonly known as 'travellers' diarrhoea'. The illness is usually self limiting, but may be debilitating during its course.
Causes of Gastroenteritis
Organisms that cause diarrhoea can be classified into two broad groups, those which invade the intestinal epithelium (e.g. Typhoid or Amoeba) and those which produce toxins that disrupt the intestinal lining (e.g. E. coli, a severe example being the recent outbreak of bloody diarrhoea and fatal Haemolytic Uraemic Syndrome in Germany caused by Enterohaemorrhagic E.coli or EHEC). This difference between invasive and non-invasive organisms provides an investigative clue because the presence of white blood cells in stool indicates colonic mucosal invasion.
Approach to Diagnosis
A diagnosis of gastroenteritis is usually made from a combination of typical clinical features such as diarrhoea which is usually non bloody (more likely bloody if it is an invasive organism), cramps, nausea or vomiting, in the context of an appropriate history of food intake often outside the patient's normal eating habits, or a history of overseas travel in recent days. The highest incidence of Travellers’ Diarrhoea is found in Latin America, Africa, the Middle East and Asia (up to 40% of travellers). In high risk areas, consumption of untreated tap water, raw fruits and leafy vegetables, undercooked meat or fish are all associated with diarrhoea. Often fellow diners are also affected. Sometimes no context can be determined. The illness is usually self limiting over a few days.
Other diarrhoeal diseases need to be excluded, such as inflammatory bowel disease (which can initially present like gastroenteritis), drug adverse effects (including pseudomembranous colitis from antibiotic usage) or even laxative abuse. Evidence of co-existing medical conditions is important, for example diarrhoea may be caused by opportunistic infections in immunosuppressed individuals. The history and physical examination should aim firstly to establish an accurate diagnosis of gastroenteritis, excluding more serious illnesses, and to determine the severity of the illness in terms of degree of dehydration and any suspicion of more serious conditions like peritonitis or toxic megacolon. The severity will determine the course of the disease and whether a patient can be managed as an outpatient, or should be admitted to hospital.
Physical examination should begin with the general status of the patient, particularly the state of hydration. Loss of more than 10% of body weight, associated with decreased skin tone or sunken eyes, or change of sensorium, is indicative of severe dehydration and requires intravenous therapy in hospital. There are often few other clinical signs. The abdomen may be generally slightly tender and peritonitis must be excluded. Per rectal examination may be useful to see the nature of stool and whether there is any blood.
Investigations are not generally necessary if a confident clinical diagnosis of gastroenteritis is made in a relatively well patient. Alarm features that should prompt further investigations include prolonged, profuse or bloody diarrhoea, pus in the stools, severe systemic illness, suspicion of Haemolytic Uraemic Syndrome or diarrhoea in an immunocompromised patient who is at high risk.
Investigations would include a blood count, urea and electrolytes, stool examination, stool cultures (often unhelpful), possibly serology and sometimes endoscopy.
Treatment usually involves oral or intravenous rehydration, rest and gradual re-introduction of a normal diet. Proprietary preparations of oral rehydration fluids are available, containing dextrose and electrolytes such as sodium, potassium, chloride, and citrate.
Milk containing food should be avoided initially because of secondary lactase deficiency. Hospitalisation is only necessary if the patient is unable to eat or drink and requires intravenous fluids, or if dehydration is severe or there is systemic toxicity.
Symtomatic relief can be provided by antidiarrhoeal agents such as Imodium or Lomotil, but unless the patient is in considerable distress, they are not recommended. Anti-emetics may be given. Antibiotics are not usually necessary even if a pathogen is identified and may even be harmful by prolonging carriage of the organism and increasing drug resistance. Antibiotics should only be given if there is prolonged diarrhoea, evidence of systemic illness, the patient is immunocompromised or specific agents such as giardia or amoeba are identified which mandate treatment. Probiotics may be helpful in shortening the course of diarrhoea particular viral diarrhoea in children.
Severe cases must be treated in hospital and in extremely ill cases, the patient may require intensive care.
Prophylactic antibiotics have been advocated for the prevention of Travellers’ Diarrhoea. There is evidence that this is effective in 80-90% of the time. There is an obvious concern that widespread use of antibiotics in this way will increase community bacterial resistance. It is more important for travellers to take sensible precautions to prevent getting gastroenteritis, such as drinking only boiled or bottled water, eating only freshly and thoroughly cooked food, avoiding salads and eating only fruit that can be peeled or personally cut. However, if it is a short but important business trip where adherence to dietary precautions is difficult, or if a patient is immunocompromised, antibiotic prophylaxis can be justified.
However in general, it should be regarded that the risk of antibiotics may outweigh the benefits of prophylaxis. Vaccines against Typhoid (effective) or Cholera (less effective) can also be taken in advance of travel.
Finally, sensible precautions should be taken by the patient who has gastroenteritis. These include keeping scrupulous standards of hygiene, as faecal matter is highly contagious, avoiding the workplace or school so as to minimise the risk of contagion to others, this being especially important for food handlers. Staff of health care facilities or community homes should take particular care as their charges may be especially vulnerable to gastroenteritis and its consequences.