Fomite-Mediated Transmission as a Sufficient Pathway

Fomite-mediated transmission can be an important pathway causing significant disease transmission in number of settings such as schools, daycare centers and long-term care facilities. The importance of these pathways relative to other transmission pathways such as direct person-person or airborne will depend on the characteristics of the particular pathogen and the venue in which transmission occurs. In this study, Kraay, et al. (2018) analyze fomite mediated transmission through a comparative analysis across multiple pathogens and venues.

The researchers developed and analyzed a compartmental model that explicitly accounts for fomite transmission by including pathogen transfer between hands and surfaces. They considered two sub-types of fomite-mediated transmission: direct fomite (e.g., shedding onto fomites) and hand-fomite (e.g., shedding onto hands and then contacting fomites). They used this model to examine three pathogens with distinct environmental characteristics (influenza, rhinovirus, and norovirus) in four venue types. To parameterize the model for each pathogen, they conducted a thorough literature search.

Based on parameter estimates from the literature the reproductive number (R0) for the fomite route for rhinovirus and norovirus is greater than 1 in nearly all venues considered, suggesting that this route can sustain transmission. For influenza, on the other hand, R0 for the fomite route is smaller suggesting many conditions in which the pathway may not sustain transmission. Additionally, the direct fomite route is more relevant than the hand-fomite route for influenza and rhinovirus, compared to norovirus. The relative importance of the hand-fomite vs. direct fomite route for norovirus is strongly dependent on the fraction of pathogens initially shed to hands. Sensitivity analysis stresses the need for accurate measurements of environmental inactivation rates, transfer efficiencies, and pathogen shedding.

The researchers concluded that fomite-mediated transmission is an important pathway for the three pathogens examined. The effectiveness of environmental interventions differs significantly both by pathogen and venue. While fomite-based interventions may be able to lower R0 for fomites below 1 and interrupt transmission, rhinovirus and norovirus are so infectious (R0>>1) that single environmental interventions are unlikely to interrupt fomite transmission for these pathogens.

Reference: Kraay ANM, Hayashi MAL, et al. Fomite-mediated transmission as a sufficient pathway: a comparative analysis across three viral pathogens. BMC Infectious Diseases. 2018;18:540