Blood Culture Anaerobic

Many publications in the past few years have indicated that anaerobic bacteremias are not as prevalent today. In most hospital studies, the incidence of clinically significant anaerobic bacteremia is less than 1%. Consequently, many experts recommend that anaerobic blood cultures be limited to those patients with gynecologic or other intraabdominal infections that are associated with anaerobes. Routine adult blood cultures are inoculated to both an aerobic and anaerobic blood culture bottle. In light of the literature recommendations, a review of blood cultures was done to determine the utility of anaerobic blood cultures at our hospital.Inpatient blood culture results were monitored for the first six months of 1997. During that time period, 70 routine anaerobic blood cultures were positive for 78 organisms. Twenty-one (27%) of these isolates were clinically significant aerobes that grew in the anaerobe bottle only. These included 6 Staphylococcus aureus, 5 Escherichia coli, 3 Methicillin-resistant Staphylococcus aureus, and one each of Serratia species, Rahnella aquatilis, Listeria monocytogenes, Vitamin B6 deficient Streptococcus, Proteus mirabilis, Group A Streptococcus, and Enterococcus faecalis. Eleven (14%) clinically significant organisms grew in the anaerobe bottle first, followed by growth in the aerobe bottle, including 4 Enterococcus faecalis, 3 E. coli, and one each Pseudomonas aeruginosa, MRSA, Torulopsis glabrata, and Group A Streptococcus. Eight (10%) clinically significant true anaerobes were isolated including one each Bacteroides distasonis, Bacteroides uniformis, Bacteroides fragilis group, Clostridium perfringens, Clostridium clostridoforme, Streptococcus intermedius, Fusobacterium species, and Prevotella bivia. The remaining thirty-eight (49%) organisms were possible or probable contaminants, and consisted primarily of coagulase-negative Staphylococcus. These findings demonstrate that despite an overall low incidence of anaerobic bacteremia, the anaerobic bottles are necessary for the recovery of fastidious and some facultative organisms. This is consistent with observations by other Bactec blood culture system users, and demonstrates the importance of using a variety of media to optimize recovery of as many types of organisms as possible.

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