Eligible for inclusion in the review were prospective or retrospective cohort and case-control studies that assessed the diagnostic accuracy of PCR-based methods for detecting Candida species. Studies had to report true positives, false positives, true negatives and false negatives.
The index tests included any PCR based method used for the identification of Candida species to generic or species level, including standard, nested, real time, or reverse transcriptase PCR, using single or multiple assays. All target genes and primers were accepted. The reference standard was based on established criteria for the definition of invasive candidiasis in neutropenic patients (EORTC criteria) and definitions used in recent clinical trials for non-neutropenic patients.
True positives were categorised into three groups. True positive I corresponded to candidaemia. True positive II corresponded to proven or probable invasive candidiasis defined for neutropenic patients by host, clinical and microbiological criteria, and for non-neutropenic patients by the isolation of Candida species from blood or other normally sterile sites in the presence of at least one indication of infection (such as inflammation at site of infection; elevated or subnormal temperature on two occasions at least four hours apart; and systolic blood pressure of ≤100 or ≥ 30mmHg below baseline) within four days prior to treatment initiation. True positive III corresponded to proven, probable or possible invasive candidiasis as indicated by host and clinical criteria without microbiological documentation for neutropenic patients, and for non-neutropenic patients by sepsis responsive to antifungal treatment with one or more risk factors for invasive candidiasis without microbiological documentation. True negative individuals were categorised into two groups: "True negative healthy" (healthy individuals) and "True negative at risk" (patients at risk of invasive candidiasis who did not fulfil the criteria for True positive III patients). Studies of PCR testing of blood cultures after incubation or after the identification of growth were excluded.
Included studies were published from 1993 to 2009. Approximately 33% of studies assessed adults alone, 15% children alone, and 15% assessed both adults and children; the remaining studies did not specify the age of the patient population. Nearly 50% the studies used standard PCR, 25% used nested PCR and 25% used real time PCR. Approximately 25% of studies used serum, whilst the remaining studies used whole blood samples (fresh or frozen stored blood samples). Most studies used rRNA genes (mostly 18S rRNA) as targets for PCR. In approximately 50% of studies, the PCR sample-processing time ranged from four to twelve hours, which allowed for the reporting of results within one working day. PCR sampling was performed prospectively in all studies.
Two reviewers independently performed study selection and disagreements were resolved by discussion and consultation with a third reviewer.