Long-term effects of a nationwide control program on the seropositivity for Trypanosoma cruzi infection in young men from Argentina

Unselected nationwide cohorts of Argentine men 18 years of age summoned for military service were tested for antibodies to Trypanosoma cruzi each year from 1981 to 1993. After an initial screening using indirect hemagglutinat ion test, the positive sera were retested by titrated indirect hemagglutina tion and immunofluorescence antibody tests at 39 laboratories or at the nat ional reference center in Buenos Aires. Nearly 1.8 million men were examine d for T. cruzi antibodies using the same standardized procedures under a qu ality assurance program. The prevalence of seropositivity for T. cruzi decr eased significantly from 5.8% in 1981 to 1.9% in 1993, but the decrease was not homogeneous among provinces within each region or constant over time. Prior to the nationwide control campaign initiated in 1961-1962, 15 provinc es had high (> 20%) percentages of houses with domiciliary infestation by T riatoma infestans bugs, which decreased to nine provinces in 1982, and four provinces in 1992. The observed decrease in the prevalence of seropositivi ty far T. cruzi may be mostly attributed to the spraying with insecticides to eliminate the domiciliary populations of Triatoma infestans. The lack of a sustainable triatomine surveillance program set a limit to the decrease of seropositivity rates and prompted a revised strategy based on community participation.