Defining Outcomes of Tuberculosis (Treatment): From the Past to the Future

Untreated active tuberculosis (TB) has a very high long-term mortality. Treatment of TB reduces mortality dramatically and should maximize cure, preventing ongoing transmission and TB sequelae. However, predicting the risk of failure and relapse is crucial for the management of individual patients and for the evaluation of effectiveness of programs. Various outcome definitions for drug-sensitive and drug-resistant TB were developed, implemented, and endorsed since introduction of TB chemotherapy by the World Health Organization (WHO), mostly based on culture and smear results. They should be applicable for individual patient care, surveillance, and research. Definitions with focus on program evaluation differ from definitions to evaluate the efficacy and effectiveness of regimens. Lack of sputum production at the later stage of treatment reduces the easy applicability of current definitions. Definitions of failure and cure are sometimes difficult to apply. Alternative approaches suggest culture positivity at 6 months or more of treatment as an indicator for failure. New definitions for cure including a relapse-free period posttreatment and reduced number of culture and smear results are considered. Increasing variation and individualization of treatment and its duration urgently require new approaches using pathogen- or host-specific biomarkers, which indicate risk of failure and define cure. Such biomarkers are under evaluation but still far from translation in clinical routine practice.