Estimated durations of asymptomatic, symptomatic, and care-seeking phases of tuberculosis disease

Ratios of bacteriologically-positive tuberculosis prevalence to notification rates are used to characterise typical durations of tuberculosis disease, but have not accounted for asymptomatic periods prior to careseeking. We developed novel statistical models to estimate progression from initial bacteriological-positivity including smear conversion, symptom onset and initial care-seeking and fitted them to tuberculosis prevalence survey and notification data (one subnational and 11 national datasets) within a Bayesian framework. Asymptomatic tuberculosis duration was in the range 4 - 8 months for African countries; three countries in Asia showed longer durations of > 1 year. Care-seeking typically began half-way between symptom onset and notification. Our method also estimated smear progression rates and case-detection ratios. We found evidence for higher case-detection ratios and much shorter durations of tuberculosis for people living with HIV. To eradicate tuberculosis transmission, greater gains may be achieved by proactively screening people without symptoms through active case finding interventions.