Quantitative microbial risk assessment to estimate the health risk from exposure to noroviruses in polluted surface water in South Africa

This study assessed the risks posed by noroviruses (NoVs) in surface water used for drinking, domestic, and recreational purposes in South Africa (SA), using a quantitative microbial risk assessment (QMRA) methodology that took a probabilistic approach coupling an exposure assessment with four dose-response models to account for uncertainty. Water samples from three rivers were found to be contaminated with NoV GI (80–1,900 gc/L) and GII (420–9,760 gc/L) leading to risk estimates that were lower for GI than GII. The volume of water consumed and the probabilities of infection were lower for domestic (2.91 × 10−8 to 5.19 × 10−1) than drinking water exposures (1.04 × 10−5 to 7.24 × 10−1). The annual probabilities of illness varied depending on the type of recreational water exposure with boating (3.91 × 10−6 to 5.43 × 10−1) and swimming (6.20 × 10−6 to 6.42 × 10−1) being slightly greater than playing next to/in the river (5.30 × 10−7 to 5.48 × 10−1). The QMRA was sensitive to the choice of dose-response model. The risk of NoV infection or illness from contaminated surface water is extremely high in SA, especially for lower socioeconomic individuals, but is similar to reported risks from limited international studies.