Transmission dynamics and control of trachoma

Trachoma continues to be the leading cause of infectious blindness. Mass administration of antibiotics is part of the current control effort, an approach which is costly when drugs are not donated. Trachoma has been shown to cluster by household and therefore this unit could be a means to target treatment. This thesis shows that active inflammatory disease is a more sensitive marker of infection within an individual’s household than just in that individual. The potential impact of a more efficient, targeted treatment of households with at least one member with active disease depends on the relative contributions of community and household transmission of infection. A mathematical model of the household transmission of ocular Chlamydia trachomatis was fitted to detailed demographic and prevalence data from four endemic populations, two in The Gambia and two in Tanzania. Maximum likelihood estimates of the household and community transmission coefficients were obtained. The estimated household transmission coefficient exceeded both the community transmission coefficient and the rate of clearance of infection by individuals in three of the study populations, indicating persistent transmission of infection within households. Allowing children and adults to have a different duration of infection improved the fit of the model to the data in three populations. For a given level of treatment coverage, targeting antibiotics to households with active disease was predicted to have similar post‐treatment dynamics to those observed after mass treatment but to be much more drug sparing. Using available cost data this approach was shown to be more cost effective when antibiotics are not donated. If targeting increases treatment coverage of diseased households, it was found to be more effective and more cost‐effective than mass treatment even if antibiotics are donated. Further work is now required to explore the feasibility of incorporating household targeted treatment into trachoma control programmes.