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A longitudinal study on reinfection with Ascaris lumbricoides was continued on a random sample of 50% of the infected population following a horizontal cross-sectional study in Okpo village, near Rangoon. The study sample was again randomly divided into two subsamples, the six-month interval worming group and the 12-month interval worming group. Microscopic examination of stool for Ascaris eggs on the 7th day and 30th day, combined with counting eggs and worming with levamisole, were carried out at two successive six-month intervals on the first subsample. Stools were examined and eggs counted on the 7th day and then monthly up to 12 months, followed by worming, in the second subsample. The worms expelled in the first 72 hours after treatment were counted. The findings over a 12-month follow-up period after one treatment included: mean monthly incidence of 20%, higher and more rapid return to previous prevalence and intensity of infection in children or 'wormy' persons than in adults or 'non-wormy' persons. Six-monthly chemotherapy definitely reduced intensity of infection in the children and adults whereas 12-monthly treatment lowered intensity in adults only. Predisposition to acquisition of high or low intensity of infection was also observed. Other findings and the implications of this study for strategies for control of ascariasis are discussed.
Hlaing et al. (Thu,) studied this question.