In Vitro and In Vivo Efficacies of Hand Sanitizers against Human Norovirus

Introduction: Human norovirus is the leading cause of acute non-bacterial gastroenteritis and foodborn disease. Contaminated hands play a significant role in the spread of the virus, particularly during food handling. Hand sanitizers are purported to interrupt norovirus transmission, but their antiviral efficacy is poorly characterized.

Purpose: This study investigates the efficacy of representative commercial hand sanitizers against human norovirus using in vitro and in vivo assays.

Methods: The current outbreak strain (GII.4 Sydney), obtained as a de-identifed stool specimen was suspended 20% in PBS and used as inoculum. Virucidal suspension assays for in vitro studies (ASTM International standard E1052) and in vivo fingerpad studies using human volunteers (n=10) (ASTM E1838) were done with exposure times of 30 and 60 sec. Virus concentrations, before and after exposure to the sanitizers, including controls, were evaluated by RT-qPCR preceded by RNase treatment.

Results: The benchmark treatment (60% ethanol) produced 0.9±0.09 log₁₀ and 1.7±0.46 log₁₀ reduction in norovirus genome equivalent copies (GEC) after 60 sec by in vitro and in vivo methods, respectively. Comparatively, a commonly used hand sanitizer containing 70% ethanol produced 2.5±0.2 log₁₀ GEC reduction after 60 sec by suspension test, and 2.0±0.4 log₁₀ reduction using the fingerpad method. With a benzalkonium chloride (BAC)-based product, 0.8 ±0.2 and 1.3±0.1. log₁₀GEC reductions were observed after 60 sec for in vitro and in vivo assays, respectively. There were no statistically significant differences (p≥0.05) between benchmark and the two commercial products by in vivo assay, although the ethanol-based product outperformed that containing BAC. Screening of additional hand sanitizers continues.

Significance: The ethanol-based product provided an additional 1.0-1.5 log₁₀ reduction in GII.4 Sydney GEC compared to water alone (0.7±0.2 log₁₀ GEC reduction after 60 sec). The results support the long held belief that hand sanitizers have some antinoroviral efficacy but cannot completely inactivate the virus.