Routine use of anaerobic blood cultures: Are they still indicated?

PURPOSE: To determine the number of patients with bacteremia and fungemia a nd to evaluate the utility of routine anaerobic blood cultures as part of t he work-up for suspected bacteremia. SUBJECTS AND METHODS: Retrospective review of microbiology data followed by selective chart review at a university-affiliated Veterans Affairs Medical Center. We determined the number of bacterial blood cultures drawn from Ja nuary 1, 1994, to December 31, 1996, and the number of anaerobic, aerobic, and fungal isolates. Chart reviews were then performed on all patients with a positive anaerobic result. RESULTS: There were 6,891 sets of blood cultures processed through the labo ratory, yielding 1,626 patients with positive results. Anaerobic isolates w ere recovered from 36 patients (2.2%) in 48 bottles. Aerobic isolates were recovered from 1550 patients (95.3%), and fungal isolates were recovered fr om 40 patients (2.5%). Seven patients (0.4%) had true anaerobic bacteremia. All seven patients had an obvious source of anaerobic infection that was k nown or suspected before the cultures were drawn. Antibiotic changes were m ade in four of these patients after the positive anaerobic results were kno wn. Antibiotic changes led to clinical improvement in one patient. CONCLUSIONS: Routine use of anaerobic blood cultures rarely results in clin ically important diagnostic or therapeutic benefits, based on the low incid ence of anaerobic bacteremia in patients who are not at increased risk. Ana erobic blood cultures should be selectively ordered in patients at risk for anaerobic infections. (C) 2000 by Excerpta Medica, Inc.