[Epidemiologic setting of the agricultural use of sewage: Valle del Mezquital, Mexico].

Wastewater from Mexico City is used to irrigate over 85,000 hectares mainly of fodder and cereal crops in the Mezquital Valley. A cross-sectional study method is being used to test the impact of exposure to raw wastewater and wastewater from storage reservoirs on diarrheal disease and parasitic infections in farmworkers and their families. The study population in the rainy season survey included 1,900 households: 680 households where the farmworker is exposed to untreated wastewater (exposed group), 520 households exposed to reservoir water (semiexposed group), and 700 households where the farmworker practices rain-fed agriculture (control group). Preliminary analysis of the data from the rainy season study (dry season study in progress) has been carried out. Current information indicates that the risk of Ascaris lumbricoides infection is much higher in the exposed group than in the control group (95% CL = 2.9-10.8). According to the procedures employed Entamoeba histolytica infection was more frequent among subjects aged 5 to 14 years from households exposed to raw wastewater, than among subjects of the same ages belonging to the control group (95% CL = 1.07-1.72). When diarrheal disease rates were analyzed, children under 5 years from exposed households had a significantly higher prevalence than controls (95% CL = 1.03-1.64). The final results of this study are expected to aid decisions within the National Wastewater Reuse Programme in Mexico.(ABSTRACT TRUNCATED AT 250 WORDS)