Figure 5
From: Mapping of UV-C dose and SARS-CoV-2 viral inactivation across N95 respirators during decontamination
Paired on-N95 measurements of UV-C dose and SARS-CoV-2 inactivation show correlated, several-fold variation in dose and inactivation across one decontamination chamber. (A) Average normalized UV-C dose (quarter-circles on-N95) and SARS-CoV-2 inactivation (circles on-N95) at measured locations on front and corner N95, colored by the normalized value. UV-C doses at two corners of the chamber floor were measured by a radiometer (large circle) and PCI (quarter-circle). Values are normalized to measurements at the apex of the front N95. Surrounding heatmap shows simulated UV-C dose. (B) SARS-CoV-2 inactivation on N95 facepieces is proportional to UV-C dose received. Selected locations on two N95 facepieces in the Spectronics XL-1000 UV-C chamber receive a 17.4 ± 5.0-fold difference in UV-C dose, which yields an 8.2 ± 1.4-fold difference in SARS-CoV-2 log reduction. Vertical dashed lines indicate the normalized UV-C dose measured by either a PCI or radiometer at monitoring sites in the chamber corners and are colored according to the heatmap in (A). Black dashed line indicates linear least squares regression on data (y = mx + b; m = 3.114 (2.038, 4.19), b = 0.3342 (− 0.3062, 0.9766); numbers in parentheses represent a 95% confidence interval on the fit parameters). Pearson correlation coefficient r = 0.8376; p-value = 1.4428 × 10–5. (C) Normalized on-N95 SARS-CoV-2 dose–response curve for 2 N95 facepieces. Datapoints represent log10(normalized SARS-CoV-2 survival), where normalized SARS-CoV-2 survival is calculated as TCID50/mL divided by the time-matched negative control TCID50/mL. Black dashed line indicates linear regression on data (y = mx + b; m = − 0.0531 (− 0.06653, − 0.03961), b = − 0.2045 (− 0.6663, 0.2574). Pearson correlation coefficient r = − 0.8842; p-value = 1.0526 × 10–7. Based on linear regression, the estimated D90 dose is between 18.83 and 19.03 mJ/cm2, depending on whether the y-intercept value is ignored or considered, respectively. In both (B) and (C), blue dashed lines denote simultaneous functional 95% prediction interval for the linear least squares regression, which indicates where the true linear regression line lies, with 95% confidence.
