Evaluation of five days protocol of aerobic incubation in automated blood culture system for optimal recovery of organisms

Background: Blood culture is the gold standard for blood pathogen detection.Automated blood culture systems such as BacT/AlertVIRTUO have revolutionized the diagnosis of Blood stream infections (BSI) enabling faster detection and improved patient care.However, the standard protocols rely on a 5day incubation period before deeming culture negative.This study investigates the potential for recovering organisms from BacT/AlertVIRTUO blood cultures flagged as negative after 5 days. Materials and Methods:The study was conducted over 6months in a tertiary care teaching hospital.The negatively flagged bottles were sub cultured onto blood agar and Sabouraud dextrose agar at the end of 5 days, 5-7 days and 7 completed days.Results: A total of 10,003 negatively flagged blood culture bottles were included in the study.On subculture of all those bottles on day 5, a total of 22 organisms were grown out of which 9 were pathogens and 13 were contaminants.On re-incubating the bottles again for 2 days (total incubation period-7 completed days), some bottles flagged positive which on further subculturing on blood agar yielded total of 44 isolates out of which all were contaminants.Unflagged bottles on final blind subculturing on day 7 yielded a single pathogen and five contaminants.All the pathogens isolated were found to be insignificant after bedside discussion with the treating clinical team.Conclusion: Prolonged incubation offers minimal clinical benefit and extending the incubation places unnecessary burden on laboratory resources increasing the cost, man power and potentially delaying the processing of other critical samples.