Body Mass Index Trajectories and Association With Tuberculosis Risk in a Cohort of Household Contacts in Southern Africa

Background Studies have demonstrated an inverse log-linear relationship between body mass index (BMI) and tuberculosis incidence. However, a person's BMI is dynamic, and longitudinal changes may be more informative than cross-sectional assessments. We evaluate the association between cross-sectional and changing BMI and risk of tuberculosis and describe longitudinal trajectories in a high-risk cohort. Methods ERASE-TB was a prospective longitudinal cohort study of household contacts ≥10 years in Southern Africa (Zimbabwe, Tanzania, and Mozambique), with 6-monthly follow-up up to 24 months. Associations between BMI and tuberculosis were investigated based on baseline (including hemoglobin) and changing BMI, using logistic, Poisson, and Cox models. Prevalent tuberculosis was defined as diagnosis during Results Of 2107 recruited household contacts (621 [29.5%] adolescents and 1310 [62.2%] female), 520 (24.7%) were underweight. There were 21 and 41 people diagnosed with prevalent and incident tuberculosis, of whom 5/21 (23.8%) and 12/41 (29.3%) were underweight. Being underweight and anemic (adjusted hazard ratio: 3.77; 95% confidence interval: 1.50-9.51) and >10% negative change in BMI during follow-up (adjusted incidence rate ratio: 2.27; 95% confidence interval: 0.22-22.9) were associated with increased risk of incident tuberculosis. The association between continuous BMI-for-age Z-scores were nonlinear, with increased risk of tuberculosis with lower BMI. Four latent groups were defined in the growth mixture modelling: increasing, decreasing, and low/high stable BMI. Conclusions Declining BMI, regardless of absolute value, is a strong predictor of tuberculosis among household contacts. Longitudinal measurements should be considered in active case finding among tuberculosis-affected households.