Regional, Household and Individual Factors that Influence Soil Transmitted Helminth Reinfection Dynamics in Preschool Children from Rural Indigenous Panamá

Background: Few studies have investigated the relative influence of individual susceptibility versus household exposure factors versus regional clustering of infection on soil transmitted helminth (STH) transmission. The present study examined reinfection dynamics and spatial clustering of Ascaris lumbricoides, Trichuris trichiura and hookworm in an extremely impoverished indigenous setting in rural Panamá over a 16 month period that included two treatment and reinfection cycles in preschool children. Methodology/Principle Findings: Spatial cluster analyses were used to identify high prevalence clusters for each nematode. Multivariate models were then used (1) to identify factors that differentiated households within and outside the cluster, and (2) to examine the relative contribution of regional (presence in a high prevalence cluster), household (household density, asset-based household wealth, household crowding, maternal education) and individual (age, sex, pre-treatment eggs per gram (epg) feces, height-for-age, latrine use) factors on preschool child reinfection epgs for each STH. High prevalence spatial clusters were detected for Trichuris and hookworm but not for Ascaris. These clusters were characterized by low household density and low household wealth indices (HWI). Reinfection epg of both hookworm and Ascaris was positively associated with pre-treatment epg and was higher in stunted children. Additional individual (latrine use) as well as household variables (HWI, maternal education) entered the reinfection models for Ascaris but not for hookworm. Conclusions/Significance: Even within the context of extreme poverty in this remote rural setting, the distinct transmission patterns for hookworm, Trichuris and Ascaris highlight the need for multi-pronged intervention strategies. In addition to poverty reduction, improved sanitation and attention to chronic malnutrition will be key to reducing Ascaris and hookworm transmission. Author Summary: Control of soil transmitted helminth (STH) infections is of central importance to improving preschool child health because these infections can have long lasting consequences on growth and development. Our study in indigenous Ngäbe preschool children in western Panama was conducted over a period of 16 months. We monitored reinfection dynamics of three STH infections (Ascaris, Trichuris and hookworm) over two reinfection cycles to gain an understanding of regional, household and individual factors that influenced transmission of these infections among preschool children. Despite the rural setting, where virtually all households live under conditions of extreme poverty, we identified spatial clusters of high prevalence of Trichuris and hookworm in the most remote and poorest area, whereas Ascaris was present throughout the study area. Preschool children who were chronically malnourished (low height-for-age) had a higher reinfection burden of Ascaris and hookworm. Household poverty (low relative household wealth and maternal education) and infrequent latrine use were also influential in Ascaris reinfection. This cross-disciplinary analysis of preschool child STH transmission in a poor rural setting provides pertinent information for STH control programs that aim to break the cycle of poverty and infection.