Is There a General Tendency for CD4 Lymphocyte Decline to Speed Up during Human Immunodeficiency Virus Infection? Evidence from the Italian Seroconversion Study

It has been suggested that the rate of CD4 cell decline accelerates in parallel with decreasing numbers of cells; however, the statistical literature suggests the opposite. CD4 cells were counted about every 6 months in a cohort of 1264 human immunodeficiency virus-infected subjects (the Italian Seroconversion Study cohort). Kaplan-Meier analysis was used to estimate the time for CD4 cells to decline by 100 cells/mm3, conditional on reaching predefined levels. In addition, CD4 cell counts were modeled as a function of time since seroconversion in individuals with > or = 5 counts. Kaplan-Meier survival times for a 100 cell/mm3 decrease in CD4 cells increased as lower counts were reached (log rank test, P < .001). The shape of the overall fitted curve of the CD4 cell counts does not suggest an increasing rate of decline. Data from the Italian Seroconversion Study cohort do not show a general tendency for accelerating CD4 cell decline in association with lower counts.