Intestinal parasitic infections among schoolchildren in Chiang Mai, northern Thailand: an analysis of the present situation.

Stool examination from primary schoolchildren in Chiang Mai Province, north Thailand, was performed to determine the present state of parasitic infections in this area. Out of a total of 491 children, 239 proved positive (48.7%). The most common type of parasite was found to be soil-transmitted helminths such as hookworm (26.3%) or Strongyloides stercoralis (11.2%), while Ascaris lumbricoides was not so prevalent (1.2% being positive in one school out of three). These results are in contrast to earlier reports showing higher prevalence rates, leading the authors to hypothesize that improvements in sanitary conditions and eradication projects have been effective. Opisthorchiasis is another parasitic disease with a relatively high prevalence rate of 7.5%. This disease rate increases with age and it was found in two out of three schools (8.3-15.8%) and was the most common type of helminth infection. Ascariasis was not seen in these two schools, but strongyloidiasis was found to be the second most prevalent helminthiasis, having a higher infection rate than hookworm. Therefore, eradication efforts now need to be directed toward eliminating opisthorchiasis and strongyloidiasis in addition to continuing to eradicate ascariasis and hookworm infections. The most common protozoal infection with a high pathogenicity in this region was found to be giardiasis (7.7%).