Spatial Distribution and Associated Risk Factors of Soil-Transmitted Helminth Infection in a Semi-urban Community in Southwest Nigeria

: Parasite distribution exhibit heterogeneity within households and communities. The aim of this study is to identify the spatial distribution, clustering and associated risk factors of Soil-transmitted Helminths infection in a semi-urban area in Southwest Nigeria. Geographical information System (GIS) was used to map the town into three density areas; low, medium and high density areas. Two hundred and thirty six soil samples were obtained from the surroundings of 137 households and stool samples were collected from the inhabitant of the households. Moran index was used to analyze the spatial distribution of STH within the community. A total of 137 households were sampled for human STH and environmental soil samples from the household were analyzed. The prevalence of human STH infection was 41.7% while that of soil parasite was 27.7% within the selected household. Ascaris lumbricoides was the predominant STH infection in the community sampled with 24.1% prevalence followed by Hookworm. Spatial analysis showed that A. lumbricoides infection was significantly clustered only in the GIS mapped medium density area of Igbo-Ora (z-score 2.302, p=0.021), while hookworm infection was randomly distributed in all the GIS mapped areas of Igbo-Ora. There was a statistically significant association between human STH infection and presence of parasite in the household soil ( x 2 5.74, p-value 0.017). None of the risk factors evaluated was found to have significant association for the clustering pattern of infection found in the medium density area of the community. Meanwhile, factors such as; the physical presence of a popularly patronized local market in the area, lack of any visible public toilet and the use of bushes around the area by the people for defecation contribute to the reasons for the clustering of the Ascaris infection. Also, the ability of Ascaris to withstand environmental conditions than other STH parasite may contribute to the pattern observed. The differences in the pattern of distribution and associated risk factors revealed that environmental conditions and exposure factors are major determinant of STH infection.