CD4 and tuberculosis: This systematic review indicates that antiretroviral therapy is strongly associated with a reduction in tuberculosis incidence in adults with CD4 counts (1) less than 200 cells/μl (HR 0.16, 95% CI 0.07 to 0.36), (2) from 200 to 350 cells/μl (HR 0.34, 95% CI 0.19 to 0.60), (3) greater than 350 cells/μl (HR 0.43, 95% CI 0.30 to 0.63), and (4) at any level (HR 0.35, 95% CI 0.28 to 0.45).