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. 2017 Sep 1;11(9):e0005872.
doi: 10.1371/journal.pntd.0005872. eCollection 2017 Sep.

Spatial distribution and risk factors of Schistosoma haematobium and hookworm infections among schoolchildren in Kwale, Kenya

Affiliations

Spatial distribution and risk factors of Schistosoma haematobium and hookworm infections among schoolchildren in Kwale, Kenya

Evans Asena Chadeka et al. PLoS Negl Trop Dis. .

Abstract

Background: Large-scale schistosomiasis control programs are implemented in regions with diverse social and economic environments. A key epidemiological feature of schistosomiasis is its small-scale heterogeneity. Locally profiling disease dynamics including risk factors associated with its transmission is essential for designing appropriate control programs. To determine spatial distribution of schistosomiasis and its drivers, we examined schoolchildren in Kwale, Kenya.

Methodology/principal findings: We conducted a cross-sectional study of 368 schoolchildren from six primary schools. Soil-transmitted helminths and Schistosoma mansoni eggs in stool were evaluated by the Kato-Katz method. We measured the intensity of Schistosoma haematobium infection by urine filtration. The geometrical mean intensity of S. haematobium was 3.1 eggs/10 ml urine (school range, 1.4-9.2). The hookworm geometric mean intensity was 3.2 eggs/g feces (school range, 0-17.4). Heterogeneity in the intensity of S. haematobium and hookworm infections was evident in the study area. To identify factors associated with the intensity of helminth infections, we utilized negative binomial generalized linear mixed models. The intensity of S. haematobium infection was associated with religion and socioeconomic status (SES), while that of hookworm infection was related to SES, sex, distance to river and history of anthelmintic treatment.

Conclusions/significance: Both S. haematobium and hookworm infections showed micro-geographical heterogeneities in this Kwale community. To confirm and explain our observation of high S. haematobium risk among Muslims, further extensive investigations are necessary. The observed small scale clustering of the S. haematobium and hookworm infections might imply less uniform strategies even at finer scale for efficient utilization of limited resources.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Map of the study area, Kwale, Kenya.
Dotted red circles indicate the catchment area from which children attend each school. The position of the participants’ houses is indicated by white circles. The river network is shown by blue lines while the main road is represented by black lines. Altitude (meters): highest, white background; lowest, dark green background.
Fig 2
Fig 2. Spatial distribution of the intensity of S. haematobium infection in the study area.
The intensity of infection was relatively high among Muslims compared to Christians despite participants sharing locality of residence. It is evident the intensity of infection is not related to the house proximity to the river. "Plus sign" schools combined because of overlap in the distribution of their populations in the study area. "Single asterisk" 1–49 eggs/10 ml urine, "double asterisks" ≥50 eggs/10 ml urine. The numbers in parentheses indicate the geometric mean of the number of eggs in each school based on religion.
Fig 3
Fig 3. Clustering of S. haematobium and hookworm infections in the study area.
The intensity was expressed as log10 (N + 1). In the left panel, S. haematobium was categorized based on WHO guidelines as: negative, light (1–49 eggs/10 ml urine) and heavy (≥50 eggs/10 ml urine) represented by white, yellow and red dots respectively. The red and white cycles show high and low risk clusters respectively. In the right panel, hookworm was grouped into negative, light (1–1999) and moderate (2000–3999) indicated by white, yellow and brown dots respectively. High risk cluster shown by red circle while the large white cycle represents the low infection cluster.

References

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    1. WHO (2013) Schistosomiasis. http://www.who.int/mediacentre/factsheets/fs115/en/. Accessed 28 August 2016.
    1. GAHI (2010) Global Atlas of Helminth Infections. http://www.thiswormyworld.org. Accessed 28 August 2016.
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