Hot chocolate: pre-warming chocolate agar improves correct organism identification from choc drop by 16.1

Introduction. Blood cultures are an important test for the diagnosis of sepsis, and the time to an accurate result can allow for optimized antibiotic therapy. The 'choc drop' is a commonly performed, reliable and cheap rapid identification method, using a drop of positive blood culture broth incubated for a short period (2-4 h) before performing matrix-assisted laser desorption/ionization time-of-flight MS on any early growth/microbiological veil present.Hypothesis. Due to the short incubation time (~2 h), agar plates may not reach the target temperature for optimal bacterial growth, leading to reduced accuracy of identification. Pre-warmed agar plates may allow for target temperature attainment more rapidly and therefore lead to more accurate identification in short-term incubation.Aim. To investigate if pre-warmed chocolate agar used for choc drop identification resulted in increased rates of correct identification.Methodology. In this study, baseline performance of choc drop identification using room temperature chocolate agar plates (n=542) was compared with an interventional period of pre-warmed chocolate agar plates (n=426).Results. Pre-warmed plates showed an increase in correct identification rate of 16.1% [95 % confidence interval (CI) 9.8%-22.4%, P=0.0013], largely due to a 17.1% (95% CI 11.1%-23.1%, P<0.0001) decrease in Gram-positive bacteria returning 'no identification'. There were slightly more errors in the interventional (n=11, 2.8%) compared with the baseline period (n=2, 0.2%).Conclusions. Pre-warming plates appears to be a cheap, effective and easy to implement method for improving the diagnostic yield of short-term incubation for rapid blood culture identification.