Process improvement and operational efficiency through test result autoverification.

Ϫ2 through 10 Ϫ7). The IC was consistently detected in dilutions 10 Ϫ6 through 10 Ϫ9. To determine interassay variation, we assayed 7 clinical samples positive for B. pertussis DNA within the linearity range of the assay 5 times on 5 different days (including reextraction each day). The SD calculated from the crossing points obtained was 0.08 –1.09. We determined in-traassay variation by assaying 3 B. pertussis-positive clinical samples within the linearity range of the assay 5 times within a single assay (including different extractions). Mean crossing points were calculated, and the SD was 0.14 –1.04. The mean melting peak was at 62 °C (range, 61.5– 62.5 °C). When clinical samples were tested, 46 of 219 nasopha-ryngeal swabs were found to be positive for B. pertussis DNA, with melting points at the expected temperature. Sera were obtained 4 weeks later from all patients with positive results and tested with the Serion ELISA classic for B. pertussis IgA (Institut Virion\Serion GmbH). A positive IgA result was obtained for all sera from patients with a positive PCR result. The new homologous IC was consistently detected in all negative and in 10 (22%) of 46 positive clinical samples. Extraction of samples was completed within 2 h. After the centrifugation step, real-time PCR took another 55 min. No contamination was observed during the entire study. PCR amplification may fail because of interference from PCR inhibitors; therefore, ICs have been incorporated in molecular assays for detection of B. pertussis (10, 13). The homologous IC used in this study was coextracted with the clinical samples and coamplified with the same primers used for the target DNA. This procedure ensures accurate control of the entire molecular assay and represents the state of the art for ICs. The B. pertussis–specific IC gave positive results for all negative samples throughout the whole study, indicating successful removal of potential inhibitors by the extraction method. Contrary to a recent study using an identical amplification protocol (13), the sensitivity of the assay in this study was not affected by introduction of the homologous IC. Sensitivity to strains other than B. pertussis may also not be affected by introduction of this IC. In 78% of positive samples, competitive inhibition prevented detection of the IC. In conclusion, the newly established assay includes all of the features required for molecular detection of B. pertussis in the routine diagnostic laboratory. This molecular assay is suitable for …