A patient on antibiotics for treatment for peritonitis presents with mucus diarrhoea. Most probable cause could be: September 2009

Ans. C: Antibiotic associated diarrhoea Nearly 25% of antibiotic associated diarrhoeas (AAD) is caused by Clostridium difficile, making it the commonest pathogen. Other pathogens implicated infrequently include Clostridium perfringens, Staphylococcus aureus, Klebsiella oxytoca, Candida spp. and Salmonella spp. Most mild cases of AAD are due to non-infectious causes which include reduced break down of primary bile acids and decrease metabolism of carbohydrates, allergic or toxic effects of antibiotic on intestinal mucosa and pharmacological effect on gut motility. The antibiotics most frequently associated with C. difficile associated diarrhoea are clindamycin, cephalosporin, ampicillin and amoxicillin. Clinical presentation may vary from mild diarrhoea to severe colitis and pseudomembranous colitis associated with high morbidity and moality. The most sensitive and specific diagnostic test for C. difficile infection is tissue culture assay for cytotoxicity of toxin B. Commercial ELISA kits are available. Though less sensitive, they are easy to perform and are rapid. Withdrawal of precipitating antibiotic is all that is needed for control of mild to moderate cases. For severe cases of AAD, oral metronidazole is the first line of treatment, and oral vancomycin is the second choice.