To meet the surveillance case definition for HIV infection
among adults and adolescents, laboratory-confirmed evidence
of HIV infection is required. The lowest CD4+ T-lymphocyte
count (or concordant CD4+ T-lymphocyte percentage of
total lymphocytes) or the presence of AIDS-defining conditions is used to determine the stage of infection. If the CD4+
T-lymphocyte count and the CD4+ T-lymphocyte percentage
are both available but do not correspond to the same severity
stage, select the more severe stage. For surveillance purposes,
disease progression is from less to more severe; once cases are
classified in a more severe surveillance stage, they cannot be
reclassified into a less severe surveillance stage.