Clostridial bacteremia in cancer patients. A 12-year experience. Over 12 years, 136 episodes of bacteremia caused by clostridial species were documented. Eighty-three were monomicrobial, and 53 were polymicrobial. Gastrointestinal, genitourinary carcinomas, and acute leukemia were the most common underlying malignancies. Septic shock occurred in 29% of monomicrobial bacteremias and 45% of polymicrobial bacteremias and was associated with a high mortality rate. Acute hemolysis, gas gangrene, and diffuse spreading cellulitis occurred infrequently but were associated with a 100% fatality rate. Many infections caused by Clostridium perfringens and C. septicum were associated with abdominal disease. The most commonly isolated organism was C. perfringens, followed by C. septicum and C. sporogenes. Overall survival was 58%, but it was 66% for monomicrobial episodes and 45% for polymicrobial infections. All of the patients with bacteremia due to an aerobic gram-negative bacillus in addition to the clostridial species died of their infection. The most effective antibiotics were clindamycin, penicillin, metronidazole, and moxalactam. Surgical drainage of abscesses was an important component of therapy. 