Comparing the Risk of M. Tuberculosis Infection among Men and Women in an African City

Background: Despite the well-known male bias in tuberculosis disease, the underlying reasons remained elusive. We examined whether male predominance in tuberculosis disease is result of higher risk of tuberculosis infection or not. If so, whether it is due to higher likelihood of exposure or higher susceptibility to infection among men. Methods: A household contact study and a prospective cohort study conducted in Kampala, Uganda, from 2013 to 2017 were used to estimate and compare prevalence and annual risk of tuberculosis infection among men and women. In household contact study, index tuberculosis cases and healthy index controls were asked to list their household contacts and extra-household contacts. All contacts were tested with tuberculin skin test to detect tuberculosis infection. In prospective cohort study, individuals with tuberculin skin test (TST) < 5 mm were enrolled and retested with the skin test at one year to detect new infection. Poisson regression with robust standard errors was used to estimate prevalence ratio and relative risk of tuberculous infection between men and women. Results: In household contact study, 123 index tuberculosis cases and 124 index controls listed 382 household contacts of tuberculosis cases, 624 extra-household contacts of tuberculosis cases, and 1044 contacts of controls. Of 1681 enrolled participants in cohort study, 1213 (72%) were retested with TST at one year. There was no sex difference in prevalence of tuberculosis infection among household contacts of tuberculosis cases, but men had a higher prevalence of tuberculosis infection among extra-household contacts of tuberculosis cases (prevalence ratio 1.25, 95% CI 1.06 – 1.48) and contacts of controls (prevalence ratio 1.53, 95% CI 1.30 – 1.81). Similarly, in cohort study, there was no sex difference in annual risk of tuberculosis infection when participant reported knowing tuberculosis cases, but men had a higher annual risk of tuberculosis infection when participants no known contact with tuberculosis (relative risk 1.94, 95% CI: 1.34, 2.80). Conclusion: Men have higher risk of acquiring tuberculous infection than women. Men and women may have the same susceptibility to tuberculosis infection given known exposure to tuberculosis cases. The observed difference in rate of infection may be partially explained by higher rates of exposure to undetected, infectious tuberculosis cases among men.