2. Design: A prospective cohort study of patients with HIV previously treated for pulmonary TB and initiated on HAART in the SAPIT (Starting AIDS treatment at three Points in TB treatment) and START (Starting Tuberculosis and Anti-Retroviral Therapy) trials. Each incident case of TB recurrence in this cohort of adult patients on HAART will be investigated to assess whether the infecting mycobacterium is similar to that from the previous infection and whether the immune responses differ in cases of relapse and re-infection.