Estimation of norovirus and Ascaris infection risks to urban farmers in developing countries using wastewater for crop irrigation.

A quantitative microbial risk analysis-Monte Carlo method was used to estimate norovirus and Ascaris infection risks to urban farmers in developing countries watering their crops with wastewater. For a tolerable additional disease burden of <or=10(-4) DALY loss per person per year (pppy), equivalent to 1 percent of the diarrhoeal disease burden in developing countries, a norovirus reduction of 1-2 log units and an Ascaris egg reduction to 10-100 eggs per litre are required. These are easily achieved by minimal wastewater treatment-for example, a sequential batch-fed three tank/pond system. Hygiene improvement through education and regular deworming are essential complementary inputs to protect the health of urban farmers.