Viricidal efficacy of a 405-nm environmental decontamination system for inactivation of bacteriophage Phi6: surrogate for SARS-CoV-2

The highly transmittable nature of SARS-CoV-2 has increased the necessity for novel strategies to safely decontaminate public areas. This study investigates the efficacy of a low irradiance 405-nm light environmental decontamination system for the inactivation of bacteriophage phi6 as a surrogate for SARS-CoV-2. Bacteriophage phi6 was exposed to increasing doses of low irradiance (~0.5 mW cm ⁻²) 405-nm light while suspended in SM buffer and artificial human saliva at low (~10 ^3–4 PFU mL ⁻¹) and high (~10 ^7–8 PFU mL ⁻¹) seeding densities, to determine system efficacy for SARS-CoV-2 inactivation and establish the influence of biologically relevant suspension media on viral susceptibility. Complete/near-complete (≥99.4%) inactivation was demonstrated in all cases, with significantly enhanced reductions observed in biologically relevant media (P < 0.05). Doses of 43.2 and 172.8 J cm ⁻² were required to achieve ~3 log ₁₀ reductions at low density, and 97.2 and 259.2 J cm ⁻² achieved ~6 log ₁₀ reductions at high density, in saliva and SM buffer, respectively: 2.6–4 times less dose was required when suspended in saliva compared to SM buffer. Comparative exposure to higher irradiance (~50 mW cm ⁻²) 405-nm light indicated that, on a per unit dose basis, 0.5 mW cm ⁻² treatments were capable of achieving up to 5.8 greater log ₁₀ reductions with up to 28-fold greater germicidal efficiency than that of 50 mW cm ⁻² treatments. These findings establish the efficacy of low irradiance 405-nm light systems for inactivation of a SARS-CoV-2 surrogate and demonstrate the significant enhancement in susceptibility when suspended in saliva, which is a major vector in COVID-19 transmission.