Gastroenteritis

Context

This is, in adults, mainly a problem in HIV positive individuals or the elderly, although clearly severe gastroenteritis of any cause can cause profound dehydration and electrolyte imbalance. Key features on history are:

• duration,
• number of stools per day,
• symptoms suggestive of postural hypotension (dizziness) or hypokalaemia (muscle weakness).

Community outbreaks suggest a food or water source, which may be fairly obvious, e.g. when a family all comes down with diarrhoea and vomiting after eating chicken bought at a freezer clearing sale. Ask about blood and mucus in the stool, which defines a dysenteric illness.

Management

Most episodes are self-limiting and settle with supportive therapy (anti-emetic if vomiting) and rehydration which will need to be intravenous if the patient is either vomiting or severely dehydrated (tachycardia in the absence of fever, postural drop in BP, or hypotension.)

Remember that some emaciated HIV positive individuals ‘normally’ run systolic BPs of 80 – 90, so this finding in isolation doesn’t necessarily imply profound dehydration. If in doubt, check serum electrolytes, urea and creatinine, and if these aren’t immediately available, rather err on the side of intravenous replacement with a potassium containing fluid (e.g. normal saline/5% dextrose with 20 to 40 mmol of KCl added.)

Antibiotics are not generally recommended for uncomplicated acute gastroenteritis. Consider their use in patients where you suspect the diarrhoea is part of a systemic sepsis syndrome, in acutely ill immunosuppressed patients, and in the elderly with a colitic/dysenteric illness. Treatable organisms are relatively uncommon (remember that many episodes are viral or due to pre-formed enterotoxins) but possibilities include Salmonella and Shigella species. Options to consider would be an oral quinolone (e.g. ciprofloxacin 500 mg 12 hourly) if not vomiting, or a third generation cephalosporin intravenously. Routine addition of metronidazole outside amoebiasis-endemic areas probably adds little, and may contribute to ongoing nausea.