Understanding virus transfer between liquid and skin is necessary to estimate transmission during water-related activities. Here, we modeled virus transfer from liquid-to-skin and skin-to-liquid. We performed human subject studies using three bacteriophages as pathogenic virus surrogates: nonenveloped MS2 and Qβ and enveloped Φ6. Our study shows that transfer from liquid-to-skin is describable by a single model based on (1) virus concentration and (2) volume of liquid remaining on skin. Contact times (0.1–30 min), and virus species had little-to-no influence on virus transfer. Likewise, liquid conditions (pH 6–9, ionic strength 10–550 mM) had no influence on transfer as shown for MS2. The model accounts for both, virus adsorbed onto the skin, and virus in the liquid retained on skin. In comparison, virus transfer from skin-to-liquid was influenced by the wetness of the skin and by liquid type (water, saliva). 90 ± 19% of the virus inoculated on the skin are transferred to the water when the skin remains wet compared to 30 ± 17% when the skin is dry. The transfer from skin-to-liquid was 41% higher when the recipient liquid was water as compared with saliva. This study quantifies virus transfer between liquid and skin and guides risk assessments of water-related activities.

Introduction. The importance of human saliva in aerosol-based transmission of SARS-CoV-2 is now widely recognized. However, little is known about the efficacy of virucidal mouthwash formulations against emergent SARS-CoV-2 variants of concern and in the presence of saliva. Hypothesis. Mouthwashes containing virucidal actives will have similar inactivation effects against multiple SARS-CoV-2 variants of concern and will retain efficacy in the presence of human saliva. Aim. To examine in vitro efficacy of mouthwash formulations to inactivate SARS-CoV-2 variants. Methodology. Inactivation of SARS-CoV-2 variants by mouthwash formulations in the presence or absence of human saliva was assayed using ASTM International Standard E1052-20 methodology. Results. Appropriately formulated mouthwashes containing 0.07 % cetylpyridinium chloride but not 0.2 % chlorhexidine completely inactivated SARS-CoV-2 (USA-WA1/2020, Alpha, Beta, Gamma, Delta) up to the limit of detection in suspension assays. Tests using USA-WA1/2020 indicates that efficacy is maintained in the presence of human saliva. Conclusions. Together these data suggest cetylpyridinium chloride-based mouthwashes are effective at inactivating SARS-CoV-2 variants. This indicates potential to reduce viral load in the oral cavity and mitigate transmission via salivary aerosols.

Infectious disease transmission is frequently mediated by the environment, where people's movements through and interactions with the environment dictate risks of infection and/or illness. Capturing these interactions, and quantifying their importance, offers important insights into effective interventions. In this study, we capture high time-resolution activity data for twenty-five Vietnamese farmers during collection and land application of human excreta for agriculture. Although human excreta use improves productivity, the use increases risks of enteric infections for both farmers and end users. In our study, the activity data are integrated with environmental microbial sampling data into a stochastic-mechanistic simulation of E. coli contamination on hands and E. coli ingested. Results from the study include frequent and variable contact rates for farmers' hands (from 34 to 1344 objects contacted per hour per hand), including highly variable hand-to-mouth contact rates (from 0 to 9 contacts per hour per hand). The frequency of hand-to-mouth contacts was substantially lower than the widely-used frequency previously reported for U.S. Office Workers. Environmental microbial contamination data highlighted ubiquitous E. coli contamination in the environment, including excreta, hands, toilet pit, handheld tools, soils, surfaces, and water. Results from the simulation suggest dynamic changes in E. coli contamination on hands, and wide variation in hand contamination and E. coli ingested amongst the farmers studied. Sensitivity analysis suggests that E. coli contamination on hands and ingested doses are most influenced by contamination of handheld tools, excreta, and the toilet pit as well as by frequency of hand-to-mouth contacts. The study findings are especially relevant given the context: no farmers reported adequate storage time of human excreta, and personal protective mask availability did not prevent hand-to-mouth contacts. Integrating high time-resolution activity data into exposure assessments highlights variation in exposures amongst farmers, and offers greater insight into effective interventions and their potential impacts.