EP-TBS-40 What can tuberculosis prevalence surveys tell us about the duration of asymptomatic bacteriologically-positive disease?

Background: Ratios of tuberculosis prevalence to notifi- cation rates are used to characterise the typical durations of tuberculosis disease. However, standard approaches ignore the spectrum of tuberculosis disease, and time with few or no symptoms prior to care-seeking. Methods: We developed novel analytical models to esti- mate progression from initial bacteriological-positivity including (depending on data): smear conversion, symp- tom onset and initial care-seeking. Case-detection ratios were also estimated by fitting the model to tuberculosis prevalence and notification data (1 subnational and 10 national datasets) within a Bayesian framework using Markov chain Monte Carlo methods. Results: For Kenya and Blantyre, Malawi individual-lev- el data were available. The sex-specific durations of as- ymptomatic bacteriologically-positive tuberculosis were 0.31 years (95% Credible Interval, CrI: 0.21-0.45) and 0.41 years (95% CrI: 0.29-0.54) for females and males in Kenya; 0.28 years (95% CrI: 0.13-0.51) years and 0.22 years (95% CrI: 0.097-0.41) in Blantyre. Age-stratified analysis of data for Kenya showed no strong age-depen- dence in durations. For Blantyre, HIV-stratified analysis estimated an asymptomatic duration of 0.13 years (95% CrI: 0.059-0.27) for HIV-positive people, shorter than the 0.46 years (95% CrI: 0.23-0.79) for HIV-negative people. Additionally, fewer cases went unnotified among HIV-positive than HIV-negative people (7% vs 29%). Analysis across 10 national datasets found asymptomatic tuberculosis durations in the range 0.3 - 0.7 years for African countries; three countries in Asia (Cambo- dia, Lao PDR, and Philippines) showed longer durations of > 1 year. For the six countries with relevant data, care-seeking typically began half-way between symptom onset and notification. Conclusion: Asymptomatic TB disease typically lasts around 6 months. We found no evidence of age-depen- dence, but much shorter durations among people living with HIV, and longer durations in some Asian settings. Time seeking care or with recognised symptoms still ac- counts for around half disease of duration.