 Well trained field health agents will first make a sketch map of the village depicting the location of houses, main water courses, snail habitats and water-contact sites and apply a household questionnaire to obtain personal data from residents to identify the individuals in the 10-19 years age range, as well as to record sanitary standards of the houses and water-contact reported behaviour as described by Pieri et al. 1998, Mem. Inst. Oswaldo Cruz, 93, Suppl 1: 259-264. 