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RT-PCR for the diagnosis of Clostridium difficile infection: the final answer has yet to come
  1. Valeria Visconti,
  2. Grazia Brunetti,
  3. Alessandra Giordano,
  4. Giammarco Raponi
  1. Department of Public Health and Infectious Diseases, Sapienza University of Rome, Roma, Italy
  1. Correspondence to Professor Giammarco Raponi, Department of Public Health and Infectious Diseases, Sapienza University of Rome, 00185 Rome, Italy; giammarco.raponi{at}

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Real time polymerase chain reaction (RT-PCR) is a powerful tool for quick diagnosis of toxigenic Clostridium difficile determination in diarrhoeic stool specimens. A two-step diagnostic algorithm (membrane enzyme immunoassay for glutamate dehydrogenase (GDH) and RT-PCR for C. difficile toxins) has been recommended by different guidelines,1 with cumulative sensitivity of 90% (80%–100%) and specificity of 88.5% (82%–95%) as compared with cell cytotoxicity assay. However, as previously reported in a subset of samples, the analysis of toxin DNA in the stool specimens is not conclusive, and indeterminate results are recorded, that is, in the case of samples with cycle threshold (CT) for toxin B with values ranging between 37.1 and 39.9.2 Until now, the rationale of the indeterminate results was undiscovered, and no interpretative criteria have been provided for these samples. In this study, we recorded indeterminate results for tcdB gene and cdt gene (binary toxin) and collected the medical history of the patients. Furthermore, indeterminate results were experimentally induced on the positive samples. The retrospective analysis of the RT-PCR curves (Xpert C. difficile, Cepheid, Sunnyvale, California, USA) …

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