Secular trends in child respiratory diseases in S. Paulo City, Brazil (1984-1996)

Objective Data from two consecutive household surveys undertaken in mid-80s and mid-90s allow to characterize and analyse secular trends irt infant an d child respiratory diseases in the city of S. Paulo, Brazil. Methods The two surveys included random population samples aged from zero t o 59 months (1,016 in the period of 1984-85 and 1,280 in 1995-96). bt both surveys the instant prevalence of high respiratory diseases (above the epig lottis) and low respiratory diseases with or without wheezing were calculat ed All sampled children were examined in their household at a random day by trained pediatricians using standardized procedures. The examinations incl uded medical history, past respiratory diseases and a complete physical exa mination. In both surveys the examinations were distributed throughout a pe riod of almost 12 months to assure a uniform coverage of the various areas of the city along the four seasons of the year. For each survey, the study of the social distribution of the diseases took into account tertiles of th e per capita family income. For the study of the determinants of secular tr ends, hierarchical causal models, multivariate regression analyses and calc ulations analogous to the ones used to assess population attributable risks were applied Results/Conclusions In the time span from the first to the second survey, t here was a substantial increase in the prevalence of both low (from 22.2% t o 38.8%) and high respiratory diseases (from 6.0% to 10.0% and from 0.8% to 2.8%, without and with wheezing, respectively). In the case of high respir atory disease and low respiratory disease without wheezing, an increase in prevalence was observed among all social strata, which did not interfere wi th the slightly less favourable situation of the lower income groups. In th e case of low respiratory disease with wheezing, the increase was only obse rved among middle and low-income groups, being particularly high among the lower income! group, yielding a significant inverse gradient between income and respiratory disease. Positive changes ill distal (family income and ma ternal schooling) and in intermediate determinants related to housing chara cteristics would have resulted in a decline, not an increase, in the preval ence of respiratory diseases in the city. The duplication in the attendance rate to day care nurseries seen in the period could have counterbalanced t he positive effect due to socioeconomic and housing variables but would nor be enough to explain an increase in the disease.