BACKGROUND:Soil Transmitted Helminth infection is one of most prevalent health problems worldwide, especially in environments with poor sanitation. Based on World Health Organisation (WHO) data, more than 2 billion people, or 24% of the world’s population, are infected with intestinal parasite. The highest prevalence is located in areas of poor sanitation and unsafe water supplies. In Indonesia, the prevalence of parasite infections is 15% of the entire population.AIM:The purpose of this study was to determine the relationship between Soil Transmitted Helminth infection on levels of eosinophils among primary school children. In addition, this study also aimed to determine the prevalence of different types of worm infections and the levels of eosinophils in children infected with worms.MATERIAL AND METHODS:This study was analytic observational using a cross-sectional method. The sampling technique was consecutive and in total 132 samples was obtained. The study involved primary school children in Amplas Medan and Hamparan Perak, Deli Serdang through May to October 2016. Univariate analysis was performed to determine STH infection prevalence and bivariate analysis was used to find the correlation between STH infection and eosinophil levels through a Chi square (χ2) test.RESULTS:The results showed that the prevalence of Soil Transmitted Helminth was 7.6%. The most common types of STH infection were 3.8% with Trichuris trichiura and 3% with Ascaris lumbricoides. A significant correlation was found between Parasite infection and eosinophil levels (Contingency Coefficient (C) = 0.2, χ2 = 5.3, p = 0.021) and the risk of STH infection that caused eosinophilia or increased eosinophil levels in the children with a Prevalence Ratio (PR) of 1.56 (Confidence Interval (CI) 95%: 1.10-2.22).CONCLUSION:It is recommended that schools at similar risk improve and maintain hygiene and healthy behaviour in the school environment and that parents and teachers pay greater attention to the cleanliness of their children.