ASSESSMENT OF THE YIELD OF ANAEROBIC BLOOD CULTURES

Because of the declining incidence of anaerobic bacteremia, the predic table sites of anaerobic infection and the increasing importance of ae robic isolates (eg; yeasts), the practice of routinely culturing half the volume of blood collected anaerobically has been questioned. We ha ve assessed the yield of routine anaerobic blood cultures in our clini cal setting. Blood culture isolates from November 1994 through October 1995 at Auckland (AKH) and Green Lane/National Women's Hospitals (GL/ NWH) were recorded. The medical records of patients with anaerobic bac teremia were examined. For the three month period April to June 1996, all positive blood cultures were analysed with respect to which bottle (aerobic or anaerobic or both) was positive. For the period November 1994 to October 1995, 5.6% and 5.3% of blood cultures at AKH and GLH r espectively were positive. At AKH and GLH anaerobes constituted 0.16% and 0.19% of all blood cultures and 3.1% and 3.5% of all positive bloo d cultures respectively. Twentyone of 25 (84%) significant anaerobes w ere from patients in whom anaerobic infection was predictable. More is olates were recovered from aerobic than anaerobic bottles, 178 versus 71, p<0.001. Aerobic culture also recovered more pathogens (76 versus 38, p<0.001 more yeasts (10 versus 0) and more Pseudomonas spp. (10 ve rsus I) than did anaerobic culture. Only obligate anaerobes were isola ted more frequently in anaerobic bottles (5 versus 0, p=0.03). Most in stances of anaerobic bacteremia occurred in patients where anaerobes c ould be expected. We conclude that routine use of two aerobic bottles with clinically directed use of anaerobic blood culture bottle is an a ppropriate and effective approach in our setting.