Application of a QMRA model for surface water treatment to investigate a waterborne outbreak of calicivirus

Other conference contribution, 2009

The QMRA modelling tool developed by the Swedish Water & Wastewater Association was applied to investigate a probably waterborne outbreak of calicivirus that occurred in the municipality of Lilla Edet, Sweden, after a period with heavy rain. Of the inhabitants that receive water from the municipal water works, 32% reported gastroenteritis in the period investigated. For the QMRA study, the pathogen load in the raw water source was estimated by describing specific discharge events of wastewater upstream the intake of the municipal water works, including dilution and transport time in the river. Estimates of the concentration of norovirus in wastewater, the efficiency of treatment processes in the waterworks, exposure volumes and dose-response relationships were based on literature data that are included in the modelling tool. In a scenario analysis, the probability of infection related to the three discharge events was quantified. The QMRA model estimated probabilities of infection comparable to the proportion of people reported estimated to have fallen ill in the epidemiological study. Sources of uncertainty and potential for improvement were identified for the in-data and for the modelling tool.