Risk profiling of hookworm infection and intensity in southern Lao People's Democratic Republic using Bayesian models

Abstract

Background: Among the common soil-transmitted helminth infections, hookworm causes the highest burden. Previous research in the southern part of Lao People's Democratic Republic (Lao PDR) revealed high prevalence rates of hookworm infection. The purpose of this study was to predict the spatial distribution of hookworm infection and intensity, and to investigate risk factors in the Champasack province, southern Lao PDR.

Methodology: A cross-sectional parasitological and questionnaire survey was conducted in 51 villages. Data on demography, socioeconomic status, water, sanitation, and behavior were combined with remotely sensed environmental data. Bayesian mixed effects logistic and negative binomial models were utilized to investigate risk factors and spatial distribution of hookworm infection and intensity, and to make predictions for non-surveyed locations.

Principal findings: A total of 3,371 individuals were examined with duplicate Kato-Katz thick smears and revealed a hookworm prevalence of 48.8%. Most infections (91.7%) were of light intensity (1-1,999 eggs/g of stool). Lower hookworm infection levels were associated with higher socioeconomic status. The lowest infection levels were found in preschool-aged children. Overall, females were at lower risk of infection, but women aged 50 years and above harbored the heaviest hookworm infection intensities. Hookworm was widespread in Champasack province with little evidence for spatial clustering. Infection risk was somewhat lower in the lowlands, mostly along the western bank of the Mekong River, while infection intensity was homogeneous across the Champasack province.

Conclusions/significance: Hookworm transmission seems to occur within, rather than between villages in Champasack province. We present spatial risk maps of hookworm infection and intensity, which suggest that control efforts should be intensified in the Champasack province, particularly in mountainous areas.

Fig 1. Smoothed age-prevalence and intensity curves of hookworm infection, Champasack province, southern Lao PDR.

Data were obtained from a cross-sectional survey carried out among 3,371 participants in 51 villages of Champasack province in 2007. Restricted cubic splines were used. For hookworm prevalence data are stratified for males (A) and females (B). For intensity of infection, only participants with an infection were included and data are presented separately for males (C) and females (D). Uncertainty is expressed as 95% confidence interval (CI).

Fig 2. Smoothed age-intensity curve for hookworm infection intensity according to village-level prevalence, Champasack province, southern Lao PDR.

Data were obtained from a cross-sectional survey carried out among 3,371 participants in 51 villages of Champasack province in 2007. The smoothed age-intensity curve is based on a restricted cubic spline of hookworm infection intensity at the unit of the village.

Fig 3. Maps of predicted hookworm prevalence (A), elevation (B), predicted hookworm infection intensity (C), and road network (D) in Champasack province, southern Lao PDR.

Predictions were based on the non-spatial mixed effects logistic (prevalence) and NB (infection intensity) models using environmental covariates only.

Fig 4. Uncertainty of hookworm predictions in Champasack province, southern Lao PDR.

Lower estimates (2.5% CL) of hookworm predicted risk (A) and infection intensity (C). Upper estimates (97.5% CL) of hookworm predicted risk (B) and infection intensity (D). CL, credible limit.