A Literature Review: Addressing Public Health Policy Questions with Chlamydia Transmission Models

Background: Chlamydia transmission models have been used to evaluate different disease prevention policy options where clinical trials would be difficult, expensive or impossible. We performed a narrative review of published chlamydia models to understand the range of modeling approaches employed, how chlamydia models have evolved over time, and how the different approaches have affected model predictions, as well as areas for further research.

Methods: We identified publications describing dynamic chlamydia transmission models used to address public health questions. We extracted information on modeling framework, including natural history and sequelae incorporated, public health aims and intervention(s) employed, outcomes measured, and study conclusions.

Results:  We found 44 publications, and a further 2 model comparison studies, where the results were based on 29 original mathematical models that met our inclusion criteria.  Nine models were individual-based, 20 were deterministic compartmental models. Apart from 2 mathematical models, the analyses were based in high-income settings. Earlier studies evaluated the benefits of national level screening programs, and estimated potentially large benefits from increased screening. Subsequent trials suggested the impact may have been overestimated, and the model comparison exercises demonstrated how different assumptions about population behavior and natural history of chlamydia affect the predictions. Modeling studies have since included more sensitivity analyses regarding modeling framework, natural history assumptions, and potential mechanisms that may reduce screening effect. Partner notification is receiving increased attention with models assessing the impact of novel prevention strategies such as expedited partner therapy.

Conclusions:  Chlamydia transmission models have identified strengths and limitations of different control strategies, but they have also revealed gaps in our knowledge of chlamydia epidemiology and natural history. Our review provides a springboard for further exploration of existing and novel interventions, their various implementation strategies, target populations, and how the known and unknown factors of chlamydia natural history may impact the estimates.