Efficiency, limit of detection, and intra-assay and interassay precision
of the RT-PCR assays. Verifications of assay sensitivity, specificity,
and precision were performed as proposed previously (27). Standard
curves ofmHEVgenotypes 3 and 4 ranging from 101 to 108 copies of HEV
plasmid DNA were used to determine the efficiency, limit of detection,
and intra-assay and interassay precision of the real-time PCR assays. For
assays A and B, which do not differentiate HEV genotypes, standard
curves for genotypes 3 and 4 were tested separately. For assays C and D,
which differentiate between HEV genotypes 3 and 4, the standard curves
were tested as duplex assays or separately in singleplex assays. The amplification
efficiency (E) for each assay was calculated according to the following
formula to determine the performance of quantitative PCR
(qPCR): E [101/S] 1, where S indicates the slope of the regression
line. The limit of detection of each assay and the intra-assay variation were
assessed with the standard curves tested in triplicate. The limit of detection
was specified as the smallest amount of DNA standard that could be
detected with 100% probability. The interassay variation was determined
by three independent runs of the standard curves in triplicate.