Contamination of shellfish waters with human noroviruses
: environmental risk factors and management options

  • Carlos Jose Alexandre De Campos

Student thesis: Doctoral ThesisDoctor of Philosophy


This thesis reports research undertaken to better understand the factors that influence norovirus (NoV) contamination in shellfish production areas (SPAs). This knowledge is necessary to develop control measures for mitigating risk from NoV contamination in SPAs. Predictive models were developed for concentrations of NoV (as measured by the reverse transcription polymerase chain reaction method) and Escherichia coli (as measured by the culture method) in shellfish from 31 harvesting sites and climatic, hydrometric, demographic and pollution source-related characteristics of upstream river catchments. Concentrations of NoV in shellfish increased as water temperature decreased and volume of sewage discharges and river flows increased. Concentrations of E. coli increased as rainfall also increased. Field studies were conducted in an estuary and in a coastal embayment to inform risk management measures for these sites. Concentrations of NoV and E. coli and their removal efficiencies were quantified in effluents from primary, secondary and tertiary treatments at four sewage treatment works. Shellfish were placed at different distances downstream of sewage discharges and tested for NoV and E. coli. Dye tracing and drogue tracking studies were conducted to quantify the dispersion and dilution of sewage effluents. Significant NoV reductions were found as sewage treatment levels increased. Activated sludge was more effective in reducing NoV than trickling filters. Norovirus was frequently detected in sewage effluents and in shellfish. It was found that a NoV limit for shellfish established at 100 copies/g would have a high compliance impact on SPAs. The dispersive characteristics of the dye-tagged effluents were consistent with the variation of NoV contamination in the study sites. A buffer zone established at 1,000:1 dilution of estuarine water to treated effluent would afford a high level of public health protection while a buffer zone established at much lower dilution ratios (e.g. 300:1) would represent a much higher health risk.
Date of Award2016
Original languageEnglish
Awarding Institution
  • Aberystwyth University
SponsorsAnimal and Plant Health Agency & Food Standards Agency
SupervisorDavid Kay (Supervisor) & Joe Ironside (Supervisor)

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