Impact of delays to incubation and storage temperature on blood culture results in tropical countries: A multi-centre study

Background: Blood cultures are one of the most important specimens processed by microbiology laboratories. Currently, there is insufficient guidance on how to transport blood cultures in low- and middle- income countries with tropical climates where delays maybe unavoidable. To fill this knowledge gap, this study investigated the effects of storage for different times and temperatures on the isolation of important bacterial pathogens. Methods and materials: In three laboratories located in Cambodia, Laos and Thailand, paediatric blood culture bottles were spiked with approximately 3 CFU/ml of Escherichia coli, Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus agalactiae, or Haemophilus influenzae. The spiked bottles were stored at 25 °C, in a cool box at ambient temperature or at 40 °C; for 0 h, 6 h, 12 h or 24 h before testing by one of four blood culture systems (two manual and two automated). All bottles were incubated until positive or for at least five days, with all growth identified. Results: No significant differences in positive bottle yields were detected when bottles were stored for 6 h (240/270, 88.9%), 12 h (233/269, 86.6%), at 25 °C (243/270, 90.0%); or in a cool box (232/269, 86.2%), when compared to no storage (80/90, 88.9%; p values > 0.05). However, significantly lower yields compared to no storage were detected when stored for 24 h (212/270, 78.5%; p = 0.030) or at 40 °C (210/270, 77.8%; p = 0.021); with the lowest yield obtained for bottles stored for 24 h at 40 °C (59/90, 65.6%; p < 0.001). The median time to positivity from inoculation increased with increased storage time; rising from 13.0 h (IQR 12.3–16.4) with no storage to 28.1 h (IQR 26.8-30.9) following 24 h of storage (p for trend < 0.001). Conclusion: Blood culture bottles should be incubated with minimal delay to maximise pathogen recovery and timely result reporting, however, this study provides some reassurance that unavoidable delays in incubating blood cultures in tropical climates can be managed to minimise negative impacts. If delays to incubation are unavoidable and are ≥12 h, transportation at a temperature not exceeding 25 °C and blind sub-cultures prior to incubation should be considered.