CD4 and tuberculosis: Results of a Cox proportional-hazard regression model, adjusted for demographic (age and gender) and clinical characteristics at ART initiation (CD4 cell count, haemoglobin, body mass index, tuberculosis and WHO stage), showed that those patients initiated on ART prior to 2011 had approximately a twofold increase in the hazards of single-drug substitution compared to those who initiated treatment during 2011 (Model 1 in Table 3).