Application of Quantitative Microbial Risk Assessment to Domestic Hygiene

Abstract

Enteric pathogens have long been a global health burden. The advancement of domestic hygiene has advanced societies for millennia as the ability to manage waste greatly reduces the public health risk of pathogen spread. The domestic restroom, more specifically the modern-day toilet is both a source and a sink for much of our residual wastewaters. With the onset and resurgence of the COVID-19 pandemic, domestic hygiene has recently become the subject of critical study to aid and inform public health intervention measures. Access to hygiene resources has shown to be impactful in the reduction of pathogen spread. The highest loads of enteric pathogens are shed in the toilet and have been utilized through wastewater epidemiology to trace, track, and inform public health prevention decisions throughout the COVID-19 pandemic. A literature review revealed that the understanding of the complexities of spread, deposition, and pathogen infection risk within the restroom is largely under-studied. Various human excreta (i.e., spit, mucous, feces urine) are exposed within the restroom and can vary with disease status (i.e., vomit, diarrhea). Understanding the transfer associations between different representative loading matrices (Model Excreta Matrices “MEM”) and human behavior within the restroom is critical to achieve more realistic Quantitative Microbial Risk Assessments (QMRA) that model risks and inform public health intervention initiatives. To our knowledge this is the first study evaluating the transfer potential of a suite of previously used indicator pathogen inoculum matrices with finger to lip contact and an important but unstudied restroom behavior, adjusting the toilet seat. For single toilet restrooms (i.e., home, small workplace, family public restrooms, hospitals), adjusting the toilet seat is more likely to be a necessity. Hand-to-toilet transfer of MS-2 coliphage was highest with the MEM of highest protein content (American Society of Standard Methods (ASTM) Tripartite soil load). Yet finger-to-lip transfer was significantly higher with the lowest protein content MEM and phosphate buffered saline. This study indicated that pathogen transfer and thereby risk of infection can vary based on the matrix in which the pathogen is shed. Further investigation through a fomite-mediated transfer multiple-scenario QMRA of SARS-CoV-2, adenovirus, and norovirus infection risk of high-touch surfaces using a Monte-Carlo simulation (10,000 events) revealed a possible domestic hygiene intervention of a post-restroom automated hand sanitizer dispenser (99.75% reduction). This research informs possible areas of improvement for QMRA studies. In order to increase the specificity of modeled simulations, more specificity is needed in the data related to exposure routes and micro activities (i.e., lifting the toilet seat) within them. We aim to provide reasoning to the benefits of a multicomponent study researching the methodological improvements and modeling needs to inform quality QMRA studies and further public health interventions.