Reinfection and infection rates of ascariasis in relation to seasonal variation in the Philippines.

Stool examinations of 320 primary school children for eggs of Ascaris revealed a prevalence of 74.0 percent. Reinfection and infection rates were determined on a monthly basis with egg-positive subjects treated correspondingly. Due to dropouts of subjects, only 154 children completed the 12-month observation. About 15% of children remained negative after treatment during one year but 85% got reinfected, with those reinfected only once being the highest then those reinfected twice, followed by those reinfected more than twice in a year. Of the 203 Ascaris worms collected 69% were females and 31% were males with a sex ratio of 2.4 females to one male; 73% were mature and 27% were immature females; 70% were mature and 30% were immature males; mean number of worms per child was 2.6. The mean length and weight of female was 22.9 cm and 3.6 gms respectively while for males it was 16.1 cm and 1.7 gm respectively. The graph showing amount of rainfall, reinfection and infection rates of ascariasis revealed the presence of two major peaks both in the reinfection and infection rates noted in December-January and May-June. Likewise, the rainfall also peaked twice namely in August and October. It appears that ascariasis reinfection or transmission is highest when rainfall is minimal and lowest when rainfall is at its highest peak. Based on the peaks of reinfection and infection, it is suggested the school children be dewormed in June and in December each year for at least three years.