The use of quantitative microbial risk assessment to estimate the health risk from viral water exposures in sub-Saharan Africa: A review

Access to microbiologically safe water is not a reality for many people throughout sub-Saharan Africa where there is widespread occurrence of viruses in water sources. Exposure to this water can lead to adverse health risks including diarrhoeal disease. To a limited extent in sub-Saharan Africa, the quantification of the human health risk associated with exposure to virally contaminated water has been done through the use of quantitative microbial risk assessment (QMRA). To understand the scope of the information available on this region, two systematic reviews were done to collect previously published literature from sub-Saharan Africa on (1) prevalence and quantification of viral contamination in water and (2) QMRAs assessing the risk from exposure to water contaminated by viruses. The results of the 2 reviews were then summarised including, for the QMRAs, exposure and dose-response assumptions, input parameters, and risk outcomes. The results found the prevalence of 10 viruses (1-100%) in drinking, ground, irrigation, surface, and waste waters from eight countries with South Africa having the most information on water contamination by viruses. Quantified viral concentration data was reported for similar to 50% of the papers, for 6 viruses (entero-, human adeno-, noro-, rota-, sapo- and Hepatitis A virus), and ranged from (10(-4)-10(11) viruses/liter). Additionally, 22 QMRAs were identified for 6 viruses (entero-, human adeno-, noro-, rota-, coxsackie B, and Hepatitis A virus) from 4 countries demonstrating that QMRA has not been used extensively in this region. The majority of these QMRAs concluded that the risk of infection, illness, or Disability Adjusted Life Year (DALY) was exceptionally high and in excess of acceptable risk limits indicating a public health concern. In conclusion, water is contaminated with viruses, risk from exposure to viruses in water is extremely high for these 4 sub-Saharan Africa countries, and QMRA is not a widely adopted methodology. Finally, some QMRA limitations were observed such as the need for more viral concentration data, collection of site- or region-specific exposure data, application of commonly used dose-response models, addressing susceptible populations such those with human immunodeficiency virus (HIV) infection in the risk characterisation, and access to free software.