Risk analysis and epidemiology: the 2006 WHO guidelines for the safe use of wastewater in agriculture

This chapter reviews the required pathogen reductions recommended in the 2006 WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater in agriculture, which are based on a tolerable additional burden of disease of ≤10–6 Disability-Adjusted Life Year (DALY) loss per person per year. The quantitative microbial risk-analysis technique, combined with 10,000-trial Monte Carlo risk simulations, is detailed here and the resulting estimates of median risk for various levels of pathogen reduction for exposure via restricted and unrestricted irrigation are also presented. This enables the selection of suitable combinations of pathogen reduction measures (wastewater treatment and post-treatment health-protection measures) to be selected, so that the resulting additional burden of disease does not exceed 10–6 DALY loss per person per year.