Onions and prevalence surveys: how to analyze and quantify tuberculosis case-finding gaps.

Finding the missing 4 million tuberculosis (TB) patients is one of the greatest challenges facing the TB community. The optimal approaches to this will vary by country, but there is no consistent process for analyzing the potential benefit of different strategies, or for deciding which approaches are most appropriate for a given setting. Here, I bring together the Onion Model-as a way to think through health system structures-and evidence from prevalence surveys. The result is a structured process for prioritizing different strategies for case finding. Outcomes vary widely by setting, pointing to the importance of each country undertaking such a prioritization process.