Time to positivity of blood culture and its prognostic value in bloodstream infection

The purpose of this study was to investigate the relationship between the time to positivity (TTP) of blood cultures and outcome in patients with bloodstream infections (BSIs). Between January 1st, 2011 and December 31st, 2013, the blood cultures of inpatients with BSI or catheter-related BSI were collected at Peking University Third Hospital. The TTP of different isolates was analyzed, and the relationship between the TTP of isolates and outcome of patients with Enterobacter BSI was retrospectively analyzed. We analyzed the TTP of 886 isolates. Escherichia coli has the shortest (11.97 ± 10.06 h) and Candida has the longest first TTP (61.62 ± 42.77 h). 68.01 % of isolates reached positivity within 24 h and 88.33 % within 48 h. Over 90 % of E. coli isolates reached positivity within 24 h. Over 50 % of Candida isolates reached positivity within 48 h. The TTP differed significantly between cultures that were single or double positive for coagulase-negative staphylococci isolates, Enterobacteriaceae, and Pseudomonas aeruginosa, and between aerobic and anaerobic cultures of E. coli (p < 0.05). However, the TTP did not differ significantly between coagulase-negative staphylococci (double positivity) and Staphylococcus aureus. The best TTP threshold for prediction of mortality from Enterobacter species BSI was 16.3 h [area under the curve (AUC) 0.730, 95 % confidence interval (CI) 0.557, 0.864, sensitivity 100 %, specificity 44.4 %]. The TTP of clinical isolates may represent a valuable marker of the clinical significance of BSIs. Laboratories and clinics should consider using the TTP to predict the prognosis of patients with BSI by bacteria, including Enterobacter and other species.