Health risks derived from consumption of lettuces irrigated with tertiary effluent containing norovirus

Wastewater is a valuable resource for water-scarce regions, and is becoming increasingly important due to the rising frequency of droughts as a result of climate change. The health risks derived from ingestion of lettuce that has been irrigated with effluent from a wastewater treatment plant (WWTP) in Catalonia (Spain) were estimated following a quantitative microbial risk assessment (QMRA) approach using site-specific data. Norovirus (NoV) was selected for this analysis, since it is the most common cause of acute gastroenteritis outbreaks in Catalonia. Two scenarios, irrigation with secondary and with tertiary effluent, were analysed. An uncertainty analysis was conducted to determine the impact of possible internalization of NoV into edible parts of the lettuce. The mean disease burden for ingestion of lettuce irrigated with secondary and tertiary effluent was 7.8 × 10− 4 Disability Adjusted Life Years (DALYs) per person per year (pppy) and 3.9 × 10− 4 DALYs pppy, respectively. A sensitivity analysis revealed that the model parameters with higher influence on the probability of disease are the concentration of NoV in the effluent and the consumption of lettuce. In order to decrease the disease burden to the guidance level of 10− 6 DALYs pppy, the tertiary treatment should be able to achieve a 4.3 log reduction of the concentration of NoV. If internalization of NoV into lettuces occurs, this would require a reduction of 7.6 log. This is the first time that site specific data and virus internalization in crops are incorporated in a QMRA of irrigation of lettuce and its impact is quantified.