The study was conducted in the rural area of S˜ao Miguel in
2001. The rural population of the municipality (population,
20 124) has 1825 houses and a population of 8469 inhabitants
(see http://www.ibge.gov.br [accessed May 2008]). Agricultural
activities are the main source of income. Six among the
thirteen census zones that comprise rural S˜ao Miguel were
randomly selected as the study site. Each census zone consisted
of three to six villages. Two villages were randomly
selected for the census zone with less than and more than,
respectively, 500 people. Households were assigned a number
within selected villages. A random number generator
was used to select 10% of the households within villages for
inclusion in the study. All residents of selected households
were eligible for the study and were enrolled using written
informed consent procedures approved by the University of
Rio Grande do Norte Ethical Committee (CEPUFRN 39/01),
Oswaldo Cruz Foundation and by the Brazilian National Ethical
Committee (CONEP number 4582).