A Bayesian Approach to Understanding Sex Differences in Tuberculosis Disease Burden

Abstract

Globally, men have a higher epidemiologic burden of tuberculosis (incidence, prevalence, mortality) than women do, possibly due to differences in disease incidence, treatment initiation, self-cure, and/or untreated-tuberculosis mortality rates. Using a simple, sex-stratified compartmental model, we employed a Bayesian approach to explore which factors most likely explain men's higher burden. We applied the model to smear-positive pulmonary tuberculosis in Vietnam (2006-2007) and Malawi (2013-2014). Posterior estimates were consistent with sex-specific prevalence and notifications in both countries. Results supported higher incidence in men and showed that both sexes faced longer durations of untreated disease than estimated by self-reports. Prior untreated disease durations were revised upward 8- to 24-fold, to 2.2 (95% credible interval: 1.7, 2.9) years for men in Vietnam and 2.8 (1.8, 4.1) years for men in Malawi, approximately a year longer than for women in each country. Results imply that substantial sex differences in tuberculosis burden are almost solely attributable to men's disadvantages in disease incidence and untreated disease duration. The latter, for which self-reports provide a poor proxy, implies inadequate coverage of case-finding strategies. These results highlight an urgent need for better understanding of gender-related barriers faced by men and support the systematic targeting of men for screening.

Figure 1.

Prevalence and case notification rates for tuberculosis, according to sex, in Vietnam (2006–2007) (A) and Malawi (2013–2014) (B). Male-to-female ratios in prevalence-to-notification ratios: 1.75 (95% credible interval: 1.21, 2.58) in Vietnam and 1.41 (95% credible interval: 0.91, 2.20) in Malawi. Dark gray bars indicate distributions for men, white bars indicate distributions for women, and lines indicate 95% confidence intervals.

Figure 2.

A sex-stratified (male and female) model of disease incidence, prevalence, and case notification rates for adult (age ≥15 years) smear-positive tuberculosis. In this model, prev_g is the tuberculosis prevalence in sex g, not_g is the case notification rate in sex g, inc_g is the disease incidence rate in sex g, ti_g is the treatment initiation rate (inverse of untreated disease duration) in sex g, sc is the self-cure rate, and mu is the untreated-tuberculosis mortality rate.

Figure 3.

Density plots for prior and posterior distributions for untreated tuberculosis disease duration, according to sex, in Vietnam (2006–2007) (A) and Malawi (2013–2014) (B). Prior distributions are shown as dashed lines, and posterior distributions are shown as solid lines. Dark gray lines indicate distributions for men; light gray lines indicate distributions for women.