Profuse Diarrhoea and Fever in an 80-Year-Old After Antibiotic Therapy

An 80-year-old woman is admitted to the acute medical unit with a 4-day history of profuse watery diarrhoea and fever. She reports passing 10 to 15 loose stools per day, with associated abdominal cramps and fatigue. She has no vomiting. On questioning, she completed a 7-day course of co-amoxiclav 625 mg three times daily five days ago for a lower respiratory tract infection. The diarrhoea started on day 5 of the antibiotic course, while she was still taking it, and has continued to worsen despite finishing the course. Her medical history includes hypertension, heart failure with preserved ejection fraction, and gastro-oesophageal reflux disease. Her regular medications are furosemide 40 mg once daily, ramipril 5 mg once daily, and omeprazole 20 mg once daily. She has been taking these medications for several months without recent changes. She lives alone and has not travelled recently. On examination, she is pyrexial at 38.9°C, tachycardic at 108 beats per minute, and hypotensive with a blood pressure of 96/58 mmHg. She is clinically dehydrated, with dry mucous membranes and reduced skin turgor. Abdominal examination reveals diffuse tenderness but no guarding or rebound. Initial investigations show a white cell count of 24.0 × 10^9/L with a neutrophil predominance, a C-reactive protein of 210 mg/L, and a creatinine of 168 µmol/L (baseline 80 µmol/L). Stool microscopy shows no ova, cysts or parasites, and nucleic acid amplification testing for Clostridium difficile toxin is positive. A diagnosis of Clostridium difficile-associated diarrhoea is made. She is started on oral vancomycin 125 mg four times daily, intravenous fluids, and electrolyte replacement. She is also started on intravenous metronidazole given the severe picture. Her diarrhoea begins to settle after 48 hours of therapy, and her fever resolves. She remains in hospital for intravenous fluids and monitoring.