Environmental risk assessment by using disability adjusted life year via constructing of a generalized linear model for morbidity estimation of waterborne pathogens.

The Environmental burden of disease (EBD) quantitatively evaluates the health impacts of pathogens by using the disability-adjusted life year (DALY) method. The life loss due to morbidity is a general expression for the EBD outcome and, thus, morbidity analysis is indispensable. Considering the deficiency of previous morbidity analysis methods, the objective of this study was to construct a linear morbidity model by using a generalized linear model (GLM) as a template and introducing exposure dose, pathogen toxicity and human immunity as impact variables. Human experimental data were collected for model fitting, and the results indicated a good fit of the majority of the pathogen data. Consequently, two practical cases of water reuse in Xi'an Siyuan University (Case 1) and Lake Cui, Kunming (Case 2) were selected for model validation. Results for case 1 indicated the major EBD to be attributed to rotaviruses (5.57 × 10-7 DALYs, 95% confidence interval (CI): 4.46 × 10-7-1.72 × 10-4 DALYs) and sprinkling irrigation (5.12 × 10-7 DALYs, 95% CI: 1.95 × 10-7-1.47 × 101 DALYs). Conversely, that for case 2 is mainly attributed to noroviruses (1.42 × 10-7 DALYs, 95% CI: 7.51 × 10-11-2.67 × 10-4 DALYs) and road flushing (1.62 × 10-7 DALYs, 95% CI: 1.16 × 10-7-2.67 × 10-4 DALYs). However, comparison with the suggested threshold of 10-6 DALYs indicated the EBDs for both cases are acceptable and, thus, water reuse is confirmed to be safe. The methodology for morbidity modelling proposed in this research can effectively compensate for missing data in DALY calculation and, thereby, help to optimize the process for EBD evaluation.