Virus isolation (VI) vs qRT-PCR. Nonparametric regression comparing the two methods of virus detection (virus isolation and qRT-PCR) in both the OPF (A) and Blood (B). qRT-PCR is shown in pink and virus isolation method is shown in blue. The predicted line and 95% confidence intervals were done using PROC LOESS (SAS version 9.3). Smoothing parameter was 1.0 for OPF both VI and qRT-PCR and Blood qRT-PCR smoothing parameter for Blood VI was 0.67.