C difficile infection recurs in about 20% of previously treated hospitalized patients. The elderly and patients with underlying colonic disease who have recently used antibiotics are at high risk. Signs and symptoms include diarrhea, abdominal pain, and leukocytosis. Diagnosis is dependent on a high degree of clinical suspicion and ELISA testing of a stool sample for toxins. Recurrence is thought to be due to the persistence of C difficile spores. Treatment can be difficult. Oral vancomycin or metronidazole for 10 to 14 days may be helpful as first-line therapy. Tapering the dose over 1 month helps destroy the spores while enabling the normal colonic flora to regrow. Probiotics, such as lactobacillus GG and S boulardii, are being developed to help restore normal colonic flora. Immunization may help prevent C difficile infection in the first place.