Reinfection with Ascaris lumbricoides after chemotherapy: a comparative study in three villages with varying sanitation.

This study examined the effect of the 2 major means of control of Ascaris lumbricoides--chemotherapy and sanitation. About 200 pre-school Caribbean children living in 3 villages with varying sanitation were studied by quantitative stool examination for the presence of the eggs of helminths. Children with Ascaris eggs were treated with piperazine. Over a 2-year period this procedure was repeated after every 6 months of natural re-infection. Results showed that (i) the rate of reinfection was on average 20% higher than the rate of new infection; (ii) there was a highly significant correlation between the results of children's initial stool examination and that 6 months later; (iii) children with high Ascaris egg counts also frequently had high Trichuris egg counts; (iv) during the 6-month intervals, 36% of the infected children were not reinfected after treatment; the difference in reinfection rates between villages with and without sanitation was 48%. Regression analysis indicated that, after several socio-economic variables were controlled, only sanitation and crowding remained significantly associated with reinfection. The implications of these findings in formulating control strategies are discussed.