Clinical impact of reducing routine blood culture incubation time from 7 to 5 days

The aim of this study was to determine the clinical impact of reducing the blood culture incubation protocol from 7 to 5 days. A laboratory data extraction identified positive blood cultures occurring after 5 or more days of incubation at Canberra Hospital, Australia between 1 January 2001 and 31 August 2011. Isolates were identified as clinically significant using a pre-existing prospective bacteraemia database. Medical records review determined whether the positive result affected clinical management. Positive blood cultures after 5 or more days of incubation accounted for 2.65% (423/15979) of all positive blood cultures, although the majority were false positives or contaminants. Eighty-five were significant/indeterminate, representing an average of eight cases per year or 0.47% (85/15979) of all positive blood cultures sets. Forty-three were isolated for the first time, representing 1.1% of all significant/indeterminate blood culture episodes. Fungi and anaerobic bacteria compromised over 50% of isolates. In 26 cases (2.4 cases per year), the culture result led to a change in patient management. A 7 day incubation protocol is preferable due to late isolation of organisms; however, if space is required to accommodate increasing blood culture numbers, reducing to a 5 or 6 day protocol would miss only a small percentage of clinically significant isolates.