The prevalence of infection by intestinal parasites in an urban slum in São Paulo, Brazil.

Sedimentation parasitological examinations were performed in stool specimens from a random household-based sample of 407 dwellers, all age groups being represented, in a slum of São Paulo, south-eastern Brazil. Intestinal parasites were detected in 45.7% of the specimens. The most prevalent parasites in this population were Ascaris lumbricoides (23.8%) and Trichuris trichiura (17.2%); only 17 individuals (4.2%) harboured Giardia duodenalis and 6 (1.5%) harboured Entamoeba histolytica. Taenia and hookworm eggs were not found. Simultaneous infection by A. lumbricoides and T. trichiura was diagnosed in 34 subjects (8.4%). The prevalence rates of infection by A. lumbricoides and T. trichiura (including those of mixed infections by both species) were highest among children aged 2-12 years. In samples positive for A. lumbricoides and/or T. trichiura, egg counts were done on Kato's thick smears and the results expressed as eggs per gram faeces (e.p.g.). The mean intensity of infection (measured as e.p.g.) in A. lumbricoides-infected subjects was highest among children aged 6-12 years and young adults under 25 years, while in T. trichiura-infected subjects the highest egg counts were observed in children aged 2-12 years. The frequency distributions of eggs of both nematodes passed by the host population were overdispersed. Moreover, a strong positive correlation (P < 0.0001) was observed between counts of eggs of both species passed by the same hosts.