Effect of delayed vial entry on the recovery and time to positivity of microorganisms from automated blood culture vials in a tertiary care hospital, South India

Recommendations by manufacturers depict that blood culture bottles are to be loaded into the automated machines as soon as possible after the blood collection. But it has been noticed that in peripheral set-ups where round the clock laboratory facility is not available or which are located far from the reference labs, or even in the tertiary care centres, delay occurs prior to the bottle loading into the instruments. In our study, we have compared the effect of pre-incubating the blood culture bottles at various temperatures like 4°C, room temperature and 37°C for various holding times, such as 2, 6, 12 and 24 hours simulating the delay in transport time in BACTEC plus Aerobic and BACTALERT FA plus systems in a tertiary care set up. We included five recent clinical isolates of different microorganisms in our study, such as Staphylococcus aurous, Streptococcus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans. Standard inoculum was prepared for each organism and 3 ml of it was added with 10 ml of citrated human blood and then inoculated into blood culture vial (BACTALERT FA plus and BACTEC Plus). Organism recovery rate, time to detection and rates of false-negativity from both the instruments were evaluated by using seeded blood culture vial and controls with delayed entry. Performance wise analysis showed that the overall isolation rate of the organisms from BACTEC bottles was higher compared to BACTALERT. Also BACTEC showed less average TTD compared to BACTALERT for Pseudomonas aeruginosa, Streptococcus and candida albicans but for E. coli and S. aureus BACTALERT showed earlier detection. To conclude, storage of the inoculated bottles at room temperature gave optimal recovery of the organisms for both BACTEC and BACTALERT systems, if delayed entry is inevitable.