Effect of 405 nm Violet–Blue Light on the Culturable Bacterial Load of Worn FFP2 Respirators

Filtering facepiece respirators accumulate a microbial load during use, and light-based decontamination methods either penetrate layered material poorly or require an added photosensitizer. Violet–blue light at 405 nm acts on photosensitizers already present in the target organisms and has been investigated in occupied healthcare environments, but not on respirators. FFP2 respirators worn for eight hours by volunteers were cut into four sections; two were irradiated at 405 nm for 90 min (4380 µW/cm2, 23.7 J/cm2) and two served as unexposed controls. The culturable load was measured on the inner surface with contact plates and within the material by immersion, and the five constituent sheets were analyzed separately. Isolates were identified by MALDI-TOF. Exposure reduced the culturable load by a median of 1.59 log10 on the inner surface and 1.79 log10 through the thickness (adjusted p = 0.016 for both). Before treatment, 60.4% of the load lay on the innermost sheet and 37.5% on the outermost; afterwards, the outermost carried 92.1% of the residue. Twenty-eight taxa were identified, dominated by coagulase-negative staphylococci. A measurable reduction was obtained in material from the full thickness of the device after irradiation of a single face, and the exposure geometry determined where the load persisted.