There was between-study heterogeneity in incidence of OIs across studies and regions, and the most important sources of heterogeneity were baseline CD4 count for cryptococcal meningitis (I2 = 56.4% for CD4 counts 200–499 cells/μL) and oral candidiasis (I2 = 54.9% for unspecified CD4 count), but no factor was identified that predominately explained the source of this heterogeneity. This evidence concerns the gene CD4 and Cryptococcal meningitis.