Browsing by Author "Owusu-Ansah, Emmanuel De-Graft Johnson"

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    Quantitative microbial risk assessment: an integrated probabilistic modeling of human exposure to norovirusin wastewater
    (2015-11-04) Owusu-Ansah, Emmanuel De-Graft Johnson
    The call for models applying quantitative data of pathogens that are of interest to replace the otherwise commonly applied models usingfecal indicator conversion ratio has gained prominence, challenges of analytical studies on virus enumeration (genome copies or particles) have contributed further to the low availability of data in Quantitative Microbial Risk Assessment (QMRA) modelling. In this thesis, a probabilistic stochastic model was developed to respond to the call for virus of interest based models. Quantitative data on genome copies of Norovirusand oocyste of Cryptosporidium spp. were applied in a QMRA model. The model was extended to include an induced immunity for Dose Response Incidence (DRI) of illness reduction in individual and population exposures, five different scenarios were modelled for Norovirusbased on the epidemiological understanding of immunity within an individual and Norovirustransmission dynamics. A third model was developed to measure the uncertainty of compliance and reliability of wastewater effluent with integrated policy standards. The probabilistic QMRA model revealed fecal indicator ratio conversion method underestimated the Disability Adjusted Life Years (DALYs) with more than two (2) orders of magnitude and were confirmed using theCryptosporidium spp. data. For immunity extended DRI models, results shows, illness incidence is much reduced when both dose-dependent and immunity are integrated into risk assessment models. Integrationof immunity only into DRI model also performed better than dose-DRI model only. It was also revealed that, irrespective of the epidemiology transmission dynamics within the population, DRI models predictions were similar and dose-immunity DRI model was better predictor. Finally, the analyses of compliance and reliabilityof wastewater effluent measurements revealed that results from wastewater effluents which met the policy standard values, in some cases could not meet the compliance level needed for effluent discharge. A chart was developed for the various wastewater treatment effluent discharge parameters for easy comparison with effluent discharges