CD4 and AIDS: Of the 27 studies meeting inclusion criteria (Table 2), several sampled high risk target populations, including patients in the pre-highly active ART (HAART) era [9], admissions to specialist AIDS facilities [64], [79], patients with low CD4+ counts [10], [78], [79], patients in regions with limited access to ART [10], [24], [25], [74]–[76], [78], [79], and individuals with psychiatric illness or drug abuse [71].