Lost to follow-up patients were younger (median age [IQR], 34.86 [31.08–38.21] versus 37.26 [33.95–42.49] years; P<0.000), and were more likely to be intravenous drug users (62.3% versus 47.7%; P = 0.029), but did not differ with respect to baseline pVL, baseline CD4 cell counts, prevalence of AIDS at baseline, or immunological responses at 6 and 12 months of HAART initiation. The gene discussed is CD4; the disease is AIDS.