Methods for estimation of associations between multiple species parasite infections

Human populations are often infected with more than one species of parasite , especially in developing countries where overall rates of parasitism are high. Infections with multiple parasite species mag not necessarily be inde pendent within an individual as physiological, immunological or ecological factors may result in positive or negative associations between infections with different parasite species. A general framework for estimation of thes e associations is presented. Data from over 215 000 individuals are analyse d and the associations between geohelminth (Ascaris lumbricoides, Trichuris trichiura and hookworm) and malaria species are investigated. A method is presented fur analysing data from multiple communities and testing whether the associations in different communities are equal. Overall estimates of t he associations between species are obtained for each country and continent where data were available. Associations between geohelminth species were, in general, found to be positive whilst both positive and negative associat ions were found between the different Plasmodium species. There was evidenc e for significant geographical heterogeneity between the associations. A me thod fur using these parameter estimates to predict the distribution of mul tiple infections when only marginal prevalence data are available is descri bed and demonstrated.