CD4 and HIV infectious disease: However, in comparison to the present study, the mean age was higher and a larger percentage of patients had CD4 nadir < 200 cells/uL in the former study [14] and the cohort was more heterogeneous in the latter, including men and women with and without HIV infection [15], which may in part account for the differences in progression rates; in addition, more than half of participants were smokers or ex-smokers in both previous studies, whereas less than half of the present patients were smokers and only 9.1% were ex-smokers.