Social inequalities as effect modifiers of active case-finding strategies for tuberculosis in Brazil: an ecological study

Background Social inequalities play a crucial role in the incidence of TB, making it plausible that they act as effect modifiers on the impact of active case-finding (ACF) strategies in the detection of the disease. We estimated the association between ACF strategies and TB detection rates and evaluated their effect modification due to social inequalities in Brazilian municipalities. Methods We included 5033 municipalities that reported at least one new TB case. We defined the TB detection rate as the outcome variable. Our exposure variables were the proportion of primary care team (PCT) reporting community-based ACF for TB and household contact investigation (HCI) of new TB cases. We also assessed the Municipal Human Development Index (MHDI) and the Social Vulnerability Index (SVI) as potential effect modifier variables. Results The TB detection rate was positively associated with both the proportion of PCTs conducting community-based ACF and the proportion conducting HCI. These associations weakened as MHDI increased (interaction incident rate ratio [IRR] 0.95, 95% CI 0.90 to 0.98 for ACF; IRR 0.93, 95% CI 0.89 to 0.96 for HCI) and strengthened with higher SVI values (IRR 1.11, 95% CI 1.02 to 1.22 and IRR 1.17, 95% CI 1.08 to 1.27, respectively). Conclusion Social inequalities in Brazilian municipalities modify the effect of ACF strategies on TB detection rates.