Anaerobic bacteremia: decreasing rate over a 15-year period.

At the Mayo Clinic, the number of cases of anaerobic bacteremia decreased 45% between 1974 and 1988. In addition, the percentage of blood cultures positive for anaerobes decreased significantly even though the total number of blood cultures performed increased. The number of anaerobic bacteremias per 100,000 patient-days also declined over the 15-year period. Organisms of the Bacteroides fragilis group ranked third in frequency with respect to other organisms that caused aerobic and anaerobic bacteremia in 1974 but ranked only seventh in 1988 and caused slightly less than one-half of the anaerobic bacteremias. The mechanisms responsible for these changes are unclear but might relate to earlier recognition and treatment of localized anaerobic infection, widespread preoperative use of agents prior to bowel surgery, and use of broad-spectrum antimicrobial regimens that include agents with activity against anaerobes.