Background: There may be an interaction between the CD4 count and the tuberculin skin test (TST) for the development of tuberculosis (TB) in human immunodeficiency virus (HIV) infected patients receiving highly active antiretroviral therapy (HAART).
Methods: Observational, cohort study of patients treated with HAART during the course of HIV infection in whom TB was confirmed by a positive culture result. Patients were stratified by TST and CD4 count. Univariate and multivariate analyses were performed to identify risk factors associated with the development of TB.
Results: The study included 1824 patients starting HAART, 339 (18.6%) of whom were TST-positive. After a median 473 days, 45 cases of TB had developed (1.9 cases per 100 person-years, 95%CI 1.38-2.54). The risk of developing TB increased significantly among patients with a positive TST (2.81, 95%CI 1.11-7.15), and in individuals with > or < 200 cells/μ l (1.37, 95%CI 0.44-4.21). By contrast, in the TST-negative group, the risk was significantly higher in patients with < 200 cells/μ l (16.64, 95%CI 2.16-127.6).
Conclusions: TST-positive patients are at high risk of developing TB, irrespective of CD4 count. However, among TST-negative patients only those with a CD4 count < 200 cells/μ l have an appreciable risk of developing the disease.