CD4 and tuberculosis: In the Cape Town treatment cohort, the highest TB rates are seen when significant person-time was spent at low CD4 cell counts (<200 cells/ mm3); an intermediate risk when CD4 cell counts were in the intermediate range of 200-500 cells/ mm3 and the lowest incidence rates when the current CD4 cell counts exceeded 500 cells/ mm3 (Fig. 5) [57].