Time to positivity of blood cultures of different Candida species causing fungaemia

This study investigated the time to positivity (TTP) for different species of Candida causing bloodstream infection and whether TTP can help differentiate fluconazole-resistant Candida glabrata and Candida krusei from other Candida species. We conducted this study at the National Taiwan University Hospital, a 2500-bed tertiary care medical centre in northern Taiwan. Patients with candidaemia were identified by central laboratory personnel from July 2010 to March 2011. TTP in each patient was determined using an automated blood culture instrument. Each patient was included only once at the time of detection of the first bloodstream infection. During the study period, a total of 329 sets of blood cultures positive for Candida were isolated from 176 patients. The mean TTP for all isolates causing candidaemia was 25.9±24.9 h. The TTP for C. glabrata was significantly longer than the TTP of the other species. In contrast, the TTP of C. tropicalis was significantly shorter than that of the other three species. The diagnostic sensitivity of TTP for C. glabrata isolates in patients with candidaemia was 93.9% (95% CI 0.798-0.993), the specificity was 66.4% (95% CI 0.581-0.741), the positive predictive value was 39.2% (95% CI 0.286-0.509), and the negative predictive value was 97.9% (95% CI 0.92-0.996) with a TTP cut-off value of >27.7 h. In conclusion, the different TTP values of different Candida species causing bloodstream infection may be helpful in differentiating C. glabrata from other Candida species.