CD4 and HIV infectious disease: Among Europeans, the strength of the association between HIV infection and allopatric lineages increased with a decreasing nadir CD4 T cell count in a dose-dependent manner: from an OR of 4.6 (95% CI 0.9–24.7) in patients with a nadir CD4 T cell count of >200 cells/μL to an OR of 12.5 (95% CI 2.6–60.8) in patients with nadir CD4 T cell counts <50 cells/μL (test for trend p<0.0001; HIV–negative patients as reference).