Targeted Treatment of Yaws With Household Contact Tracing: How Much do we Miss?

Abstract

Yaws is a disabling bacterial infection primarily found in warm and humid tropical areas. The World Health Organisation strategy mandates an initial round of total community treatment (TCT) with single-dose azithromycin followed either by further TCT or active case finding and treatment of cases and their contacts (the Morges strategy). We wish to investigate the effectiveness of the Morges strategy. We employ a stochastic household model to study the transmission of infection using data collected from a pre-TCT survey conducted in the Solomon Islands. We use this model to assess the proportion of asymptomatic infections that occur in households without active cases. This analysis indicates that targeted treatment of cases and their household contacts would miss a large fraction of asymptomatic infections (between 65% and 100%). This fraction actually increases at lower prevalences. Even assuming that all active cases and their households are successfully treated, our analysis demonstrates that at all prevalences present in the dataset, up to 90% of (active and asymptomatic) infections would not be treated under household-based contact tracing. Mapping was undertaken as part of the study "Epidemiology of Yaws in the Solomon Islands and the Impact of a Trachoma Control Programme", September-October 2013.