Methods for SARS-CoV-2 hospital disinfection, in vitro observations

Abstract

Introduction: Escalation of chemical disinfection during the COVID-19 pandemic has raised occupational hazard concerns. Alternative and potentially safer methods such as ultraviolet-C (UVC) irradiation and ozone have been proposed, notwithstanding the lack of standardized criteria for their use in the healthcare environment.

Aim: Compare the virucidal activity of 70% ethanol, sodium dichloroisocyanurate (NaDCC), chlorhexidine, ozonated water, UVC-222 nm, UVC-254 nm against three SARS-CoV-2 variants of concern cultured in vitro.

Methods: Inactivation of three SARS-CoV-2 variants (alpha, beta, gamma) by the following chemical methods was tested: ethanol 70%, NaDCC (100 ppm, 500 ppm, 1000 ppm), chlorhexidine (2%, 1% and 0.5%), ozonated water 7 ppm. For irradiation, a je2Care 222nm UVC Lamp was compared to a Sylvania G15 UV254 nm lamp.

Results: Viral inactivation by >3 log was achieved with ethanol, NaDCC and chlorhexidine. The minor virucidal effect of ozonated water was <1 log. Virus treatment with UVC-254 nm reduced viral activity by 1-5 logs with higher inactivation after exposure for 3 minutes compared to 6 seconds. For all three variants, under equivalent conditions, exposure to UVC-222 nm did not achieve time-dependent inactivation as was observed with treatment with UVC-254 nm.

Conclusion: The virucidal activity on replication-competent SARS-CoV-2 by conventional chemical methods, including chlorhexidine at concentrations as low as 0.5%, was not matched by UVC irradiation, and to an even lesser extent by ozonated water treatment.

Keywords: Chlorhexidine; Ozonated water; SARS-CoV-2; Sodium dichloroisocyanurate; Ultraviolet-C; Virucidal.

Figure 1

Activity of SARS-CoV-2 exposed to conventional chemical methods, ozonated water and ultraviolet irradiation. Viral activity of three variants of concern exposed to chlorhexidine at 0.5–2% (A), sodium dichloroisocyanurate (NaDCC) at 100–1000 ppm (B), ethanol 70% (C), ozonated water at 7 ppm (D), UVC-254 nm (E) and UVC-222 nm (F) in relation to non-treated virus (control) represented as TCID₅₀/ml. Reduction of viral activity below the detection limit (>3 log relative to the control) is indicated by the horizontal dashed line. Time of exposure was 3 minutes unless otherwise specified. One representative experiment of two replicates is shown.