Enviromental Infection Transmission: Routes of Transmission for Influenza and Other Agents

Abstract

Most infections that are assumed to be $directly$ transmitted have some environmental component between excretion and exposure, in which pathogens exists in the environment before exposure, potentially initiating infection in a susceptible. Modeling a potentially infection transmitting contact involves implicit pathogen transfer from a contagious person, animal, or other entity, to a susceptible person. Traditional transmission models use an abstract and usually poorly defined concept of $contact$ to transmit infection. This dissertation models detailed processes leading to transmission that more closely resemble processes that do so in reality by modeling the ex-homo intermediate environmental stage of pathogen existence. This allows us to investigate unique issues that conventional transmission models are unable to address, such as examining factors that alter transmission mode strength, as well as assessing the effect of environment-based interventions such as hand hygiene or surface decontamination. We use both an individual based as well as a deterministic compartmental modeling framework to model transmission through the environment, either via aerosol, direct droplet-spray, or contact-mediated transmission whereby pathogens are excreted to the fomite environment, later picked up by susceptibles, and eventually self-inoculated to potentially cause infection. We found that either aerosol, direct droplet-spray, or contact mediated transmission routes may cause high transmission either each on their own or in combination with one another, given realistic parameter values. We also found that increasingly non-random touching may either increase or decrease contact transmission, depending on the degree of shedding to one's own hands; hand hygiene became more effective as touching became more specified to specific objects in the environment, while when touching is quite random, broad surface decontamination is most effective. Finally, we found that norovirus and S. aureus were much more transmissible via the contact mediated route compared to influenza and rhinovirus, but that they were also much more amenable to hand hygiene or surface decontamination intervention.Ph.D.Epidemiological ScienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/84440/1/ispickna_1.pd