Of masks and methylene blue—The use of methylene blue photochemical treatment to decontaminate surgical masks contaminated with a tenacious small nonenveloped norovirus

Here Comes the Sun—Methylene Blue in Combination with Sunlight Sanitises Surgical Masks Contaminated with a Coronavirus and a Tenacious Small Non-Enveloped Virus

“…Meanwhile, methylene blue treatment prior to exposure resulted in consistent and superior decontamination, achieving a titre reduction of 4.36 (±0.11) log 10 TCID 50 /mL for the former, and 4.53 (±0.14) log 10 TCID 50 /mL for the latter condition. These infectious MNV titre reductions mirrored norovirus decontamination efficacies previously achieved by our team leveraging an artificial LED light source (30 min of red light exposure) [25]. While the dependence of the 30 min exposure protocol on high-illuminance sunlight is a clear constraint in the mid-latitudes (circa 45 • C latitude), as well as the Arctic and Antarctic circles, it is likely to be a lesser concern in equatorial and tropical zones of the globe (0 to 23.5 • latitude) where sunlight intensity is roughly greater by 20-30% [36].…”

“…The workflow followed previously described protocols for SM inoculation with PRCV and MNV [15][16][17][18]25]. Per SM, 100 µL of undiluted viral suspension was injected under the first outer layer at the centre of each of the three square coupons (34 mm × 34 mm).…”

“…Virus-inoculated SMs were placed horizontally and were sprayed with a total volume of 7-8 mL of either a 10 µM (for assays involving PRCV) or 100 µM (for assays involving MNV) methylene blue solution (Sigma-Aldrich (M9140); solution prepared in deionised water; final volume determined based on six repetitive sprays into a graduated cylinder). The choice of a ten-fold higher methylene blue concentration for the treatment of noroviruscontaminated SMs was based on previously published experimental protocols describing the adaptation of the original DeMaND protocol (implementing 10 µM methylene blue for coronavirus inactivation) to the decontamination of small non-enveloped viruses [25]. In total, each SM was sprayed four times on the outer side and twice on the inner side (facing the wearer).…”

“…For its application to PPE decontamination, contaminated materials were spray-coated with methylene blue and were subsequently exposed to a visible bright light source (custom-built LED light boxes with an output of either 12,500 lux of red light or 50,000 lux of white light) for 30 min. We subsequently adapted this protocol to the decontamination of a highly resistant, small, non-enveloped norovirus, utilising the murine norovirus (MNV) surrogate to model the inactivation of notoriously tenacious [23,24] human noroviruses [25].…”