Evaluation of nested and real-time PCR assays in the diagnosis of candidaemia

Abstract

Polymerase chain reaction (PCR) assays have a very low theoretical detection threshold and are therefore advocated for the diagnosis of fungaemia. However, their effectiveness in this respect remains to be assessed. This study compared real-time PCR (Can-G) and nested PCR assays with blood culture for the diagnosis of Candida spp. bloodstream infections. A total of 200 clinical blood samples obtained from 110 patients at risk for developing a systemic fungal infection, hospitalized in the University Hospital of Sfax (Tunisia), were submitted to testing by culture, nested PCR and real-time PCR. Blood culture was positive in 36 patients. When compared with culture, the Can-G assay (81% sensitivity, 96% specificity) performed better than the nested PCR assay (86% sensitivity, 54% specificity). The real-time PCR assay, which avoids both the contamination hazard with amplicons that may cause false-positive results and the use of time-consuming post-PCR steps, appears more suitable than the nested PCR assay for the laboratory diagnosis of Candida spp. bloodstream infections. In this study, real-time PCR did not enhance the diagnostic sensitivity for Candida spp. bloodstream infections compared with conventional blood culture; however, it may lead to earlier implementation of an adequately targeted antifungal treatment.