Fomite-mediated transmission as a sufficient pathway: a comparative analysis across three viral pathogens

Abstract

Background: 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. Here we analyze fomite mediated transmission through a comparative analysis across multiple pathogens and venues.

Methods: We developed and analyzed a compartmental model that explicitly accounts for fomite transmission by including pathogen transfer between hands and surfaces. We consider 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). We use 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 we conducted a thorough literature search.

Results: Based on parameter estimates from the literature the reproductive number ([Formula: see text]) 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, [Formula: see text] 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.

Conclusions: 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 [Formula: see text] for fomites below 1 and interrupt transmission, rhinovirus and norovirus are so infectious ([Formula: see text]) that single environmental interventions are unlikely to interrupt fomite transmission for these pathogens.

Keywords: Environmental Infection Transmission System (EITS); Fomite mediated transmission; Mathematical model; SIR epidemic model.

Fig. 1

Model diagram Model tracks people (in compartments S, I or R) and pathogens on fomites (F) and hands (H_S, H_I, H_R). The six events (inoculation, fomite touching, excretion, pathogen inactivation recovery and cleaning) are represented by arrows in the direction of the corresponding flow

Fig. 2

a The persistence duration on hands and fomite-hand transfer efficiency of the three pathogens examined. b Examples of three different venues as characterized by their proportion of accessible surfaces and the rate of contact with those surfaces

Fig. 3

Reproduction numbers ${\mathcal{R}}_0$ as a function of fomite touching rate (ρ_T) and proportion of touchable surfaces (λ)

Fig. 4

Contours for the ratio $\frac{R_C}{R_0}$ for cleaning strategies consisting of hand washing three times a day and surface decontamination at varying frequency (Solid lines). Green regions indicate venues where R_C<1, i.e. the interventions successfully prevent an outbreak. The results for each pathogen (influenza, rhinovirus, and norovirus) are summarized by column, while different strategies are shown by row. Surface cleaning is performed every two days (top row), once a day (middle row), or two times a day (bottom row). Hand washing occurs three times per day for each row