Patterns of soil-transmitted helminth aggregation in the human host population after several years of intensive mass drug administration

Background Community-wide mass drug administration (cMDA) is known as an effective, albeit costly, control strategy for soil-transmitted helminth (STH) parasites. A better understanding of STH aggregation after many rounds of cMDA could help shape more cost-effective policies.Methods This analysis uses data from the Geshiyaro project, aiming to break STH transmission by cMDA and water, sanitation and hygiene interventions. Ascaris lumbricoides infection prevalence is derived from egg count data and parasite aggregation is obtained by fitting a negative binomial distribution to the frequency distribution of faecal egg counts.Results The relationship between parasite dispersion and infection prevalence is approximately linear. Parasite aggregation increases as infection prevalence decreases.Conclusions A minority of individuals carry most parasites as prevalence decreases in the community. These individuals could be selectively targeted for repeated treatment.