Setting: Tertiary care chest hospital in Montreal, Canada, where the average annual incidence of TB is 10/100,000 population.
Objectives: To evaluate the clinical correlates of humoral response to three Mycobacterium tuberculosis antigens.
Methods: Humoral response to three M. tuberculosis antigens, 38 kDa, 14 kDa and ESAT-6, was measured with ELISA in patients with a spectrum of TB-related conditions. The association of positive tests for each antigen, defined with receiver operator characteristics (ROC) analysis, and patient characteristics was assessed in multivariate regression.
Results: A total of 383 patients underwent serologic testing. In multivariate analysis, humoral response to 38 kDa was associated with active disease, response to 14 kDa was associated with inactive TB and female sex, and response to ESAT-6 with inactive TB, female sex, prior contact with TB, and recent arrival in Canada from high prevalence countries.
Conclusions: Response to the 38 kDa antigen was associated with current active disease, and was very different from response to the 14 kDa and ESAT-6 antigens. These latter two antigens were associated with risk factors for future active, but not current disease, suggesting that they might be useful to identify persons with higher risk of reactivation of latent TB.