COMPARISON OF 5 DAYS VERSUS 7 DAYS OF INCUBATION FOR DETECTION OF POSITIVE BLOOD CULTURES BY THE BACTEC-9240 SYSTEM

The specimen capacity of blood culture systems is determined by the le ngth of time that blood cultures are incubated. Since the patient popu lations served by hospitals vary, individual laboratories should evalu ate the relative cost and benefits of different testing regimens for t heir particular setting. To be cost-effective, the use of a 5-day rath er than a 7-day protocol for the Bactec 9240 system (Becton Dickinson Diagnostic Instrument Systems, USA) has been recommended. To evaluate whether the shorter schedule would be appropriate at the Microbiology Laboratory at the National Cheng Kung University Medical Center in Tai nan, Taiwan, the yield from 5 days versus 7 days of incubation was com pared using a total of 9653 blood specimens collected from 1 April to 30 September 1997. Of the 1848 positive vials, 1822 (98.6%) were posit ive in the first 5 testing days; only 26 (1.4%) were positive on day 6 or 7. Only five of the latter vials were judged to contain clinically significant organisms: one Cryptococcus neoformans, one Candida albic ans, one Enterobacter cloacae, one Klebsiella pneumoniae, and one Prot eus mirabilis. Two vials contained organisms whose clinical significan ce was categorized as unknown, while 19 contained organisms that were considered contaminants. These data suggest that, for the laboratory s tudied, the 5-day protocol for the Bactec 9240 system is more cost-eff ective than the 7-day protocol and is adequate for detection of positi ve blood cultures.