Discussion

The results of this study indicate that 45/45 seconds of both side irradiation is an effective and efficient reprocessing concept for the viral decontamination of FFP2 masks. An irradiation time of 30/30 seconds did not lead to a sufficient decontamination for both mask models. As this result does not seem to be model dependent, only “Bluebec BB 203” were used for the following irradiations with 45/45 seconds and 60/60 seconds. Irradiation for 45/45 seconds or more was sufficient to successfully decontaminate each sample.

In comparison to other studies on the UV-C doses required for viral decontamination of respiratory masks, the doses indicated in the present study are higher.Reference McKinney and Pruden ^{5 –}Reference Masjoudi, Mohseni and Bolton ⁷ While the method developed in the present study requires 45 seconds of irradiation per side (translating into 427.5 $ \frac{mJ}{cm^2} $ per side), a similar study by Fisher and ShafferReference Fisher and Shaffer ⁶ found a dose of 100 $ \frac{mJ}{cm^2} $ to be sufficient for successful disinfection of MS2 bacteriophage in FFP2 masks. One reason for these differences may be the more realistic use of whole masks for irradiation in the present study instead of the circular excisions used by Fisher and Shaffer.Reference Fisher and Shaffer ⁶ As discussed in Vaupel et al.,Reference Vaupel, Fengler and Mutters ¹ the positioning of the masks and possible shaded zones could increase the UV-C dose required for decontamination.Reference Baluja, Arines and Vilanova ⁸ The decontamination method developed in this study is intended for the efficient and rapid, high throughput reprocessing of whole masks in real life settings and not intended for the investigation of the lowest possible irradiation doses. Therefore, higher doses are plausible and necessary to ensure the effectiveness of the presented method.

Another method-specific reason for the comparatively high UV-C dose reported in the present study could be that the dried virus suspension with cell culture medium on the masks may have a shielding effect that leads to a higher required UV-C dosage.Reference Ratnesar-Shumate, Williams and Green ^{9 ,} Reference Biasin, Bianco and Pareschi ¹⁰ This was already shown by Ratnesar-Shumate et al.,Reference Ratnesar-Shumate, Williams and Green ⁹ who also demonstrated that the required UV-C dose for viral inactivation is significantly lower with simulated saliva than with culture medium. In a real-life setting, where the presented method is used to decontaminate worn FFP2-masks, that may contain saliva but no cell culture medium, the presented method would be even more effective.

In conclusion, the 30/30 seconds irradiation concept presented by Vaupel et al.Reference Vaupel, Fengler and Mutters ¹ is not applicable for the decontamination of viable viruses. However, 45/45 seconds of irradiation proved to be effective to inactivate viable enveloped respiratory viruses like Influenza H1N1 on FFP2 masks. The combination of both studies indicates that a both side irradiation of 45 seconds per side (corresponding to a total of 21.38 $ \frac{J}{25\;{cm}^2} $ ) is an efficient method to inactivate both bacteria and viruses on both sides of a mask. Further investigations, especially investigations on the same mask model (Bluebec BB 203) with parallel contamination of bacteria and viruses with larger sample sizes, are expedient to detect possible environmental influences, errors in handling, and other factors influencing the irradiation result.