Fig. 4.

Evaluation of the extraction efficiency of infective HCoV-OC43 particles from 10 cm (panel A) glass-fiber filters when using a combined shaking and vortexing procedure. In both panels, the titers of filter-recovered HCoV-OC43 are expressed as a percentage of the titer of the inoculated virus (% of recovery = (FFU recovered × 100)/FFU inoculated), and error bars represent the SEM of independent experiments. In panel B, the dispersion of the different percentages of recovery obtained with the shaking-vortexing and using DMEM + 40%FBS (10 cm glass-fiber filters) are depicted; the horizontal line represents the mean value of 16 independent experiments, while the error bars represent the SEM of independent experiments. In panel C, a linear regression analysis correlates for each eluate obtained with the combined shaking and vortexing procedure (10 cm glass-fiber filter; eluent: DMEM + 40%FBS), the FFU recovered with the respective threshold cycles (Ct) measured with the RT-PCR. 95% CI: 95% confidence interval; R² = square of the correlation coefficient.