FIG. 2.

Serial 10-fold dilutions of the viral culture supernatant prepared in HAV RNA-negative human plasma were spotted and kept at room temperature for 24 h. Difference plots are shown. To assess a possible loss of HAV RNA induced by the blotting process, the viral loads of spotted and nonspotted dilutions were determined by quantitative RT-PCR. (a) After applying the 4.5 correction factor that accounts for the dilution of a blotted specimen, a nonsignificant bias toward lower viral loads obtained after blotting was shown by the Bland and Altman model, indicating a mean difference of 0.34 log copies/ml (bias 95% CI = −0.48 to −0.19). (b) HAV viral loads were determined in 26 HAV RNA-positive sera and in matched DSS samples kept at room temperature for 24 h. Four DSS samples could not be quantified after blotting: two matched sera had viral loads of <100 copies/ml, and two had 2.11 and 2.22 log copies/ml. Among the 22 quantifiable DSS, no significant bias toward lower viral loads obtained after blotting, as shown by the Bland and Altman model, indicating a mean difference of 0.1 log copies/ml (bias 95% CI = −0.48 to −0.19).