Detection of candidaemia in high risk patients: can yield of blood cultures be improved by blind subculture?

Rapid detection of candidaemia is crucial for timely antifungal chemotherapy. However, the sensitivity of automated blood culture (BC) systems has been questioned. Blind subculture might increase detection rate and possibly also reduce time to detection of candidaemia. This retrospective study aimed to evaluate the efficacy of blind subcultures in patients deemed at high risk of candidaemia. BCs were processed by the BacT/Alert BC system, and during a 5-y period (1998-2003) subculture on the third d of incubation was performed for patients selected by clinical and microbiological assessment. A total of 79,165 BCs were drawn during the study period. 2154 BCs from 285 patients were selected for subculture. 103 (4.8%) BCs from 52 patients were yeast positive; 71 were detected positive prior to the planned subculture, 25 were positive on subculture, and 7 were negative on subculture, but became positive during further incubation. The 25 BCs positive on subculture originated from 14 patients, 11 of whom had already been diagnosed with candidaemia during the previous 14 d. Thus, a primary diagnosis of candidaemia was obtained by subculture in only 3 (1.1%) of the 285 patients selected. In conclusion, in our clinical setting blind subculture did not materially increase the detection of candidaemia, but helped to document persistent infection in a subset of cases.