The purpose of this study was to adapt and evaluate the model developed by Nicas and Best ( 3) to estimate probability of infection from enteric and respiratory viruses in a workplace setting. No previous studies were found in the literature reporting estimated pathogen loading on hands from contact with fomites evaluated with real-time environmental sampling. ( 2) presented a hypothetical evaluation of the micro-activity approach to assessing risk of rotavirus infection in daycare settings, but they also did not evaluate their model with experimental data. Although they presented a hypothetical evaluation of their model by estimating the infection risk of influenza A in the workplace, they did not evaluate their model with empirical data. Nicas and Best ( 3) recently developed a model to estimate the dose of pathogens transferred to facial mucus membranes, while considering the rate of pathogen transfer to hands via contact with fomites, pathogen die-off rates on the hands, and pathogen transfer from hands to source. ( 7) These micro-activities have then been successfully used to evaluate exposure models for contaminants such as lead and pesticides.
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( 6) Techniques have been developed using videography and specialized software to transcribe micro-activities (e.g., hand-to-mouth frequency). For example, children have been shown to contact an average of more than 500 objects per hour with their hands with a median duration of 3 seconds.
Measurements of contact rates are difficult because of the high frequency and relatively short duration of these activities. ( 2– 5) The limited number of models results, in part, from the difficulty in obtaining the detailed activity data needed to generate quantified estimates of contact rates between hands and fomites, hands and mucus membranes, and fomites and mucus membranes. ( 1) Although the incidence of illnesses resulting from indirect routes could be significant, it is difficult to estimate the relative risk of indirect transmission because of the variability and uncertainty in human behavior, varying viral concentrations on fomites, and other exposure factors such as transfer between surfaces and virus survival rates on different surface types.įew models exist that facilitate quantitative correlation of viral concentration on fomites with infection risk, while considering variable individual behaviors that influence the indirect viral transmission. This is the first published study to successfully evaluate a model focused on the indirect transmission of viruses via hand contact with measured data and provide an assessment of the micro-activity approach to microbial risk evaluation.Ĭommon respiratory and enteric viruses are readily spread among populations living and working together through direct transmission (i.e., inhalation of droplets from coughing and sneezing or ingestion of contaminated foods and beverages), as well as through indirect transmission via contact with contaminated surfaces and hand-to-mucus membrane contact.
The model was then used to demonstrate that the Healthy Workplace Project™ intervention significantly reduced risk of infection by 77% for rotavirus and rhinovirus. Following the Monte Carlo simulations (n=1,000), the estimated phage loading on hands was not significantly different from the loading of phage on hands measured in the experimental trials. Parameter distributions were developed from this data, as well as for micro-activity rates, contact surface areas, phage transfer efficiencies, and inactivation rates. To evaluate the model, measurements of phage loading on fomites and hands collected before and after implementation of a Healthy Workplace Project™ intervention were used. The purpose of this study was to evaluate the micro-activity approach for assessment of microbial risk by adapting a mathematical model to estimate probability of viral infection from indirect transmission. Although the number of illnesses resulting from indirect viral pathogen transmission could be substantial, it is difficult to estimate the relative risks because of the wide variation and uncertainty in human behavior, variable viral concentrations on fomites, and other exposure factors.
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