CD4 and AIDS: HIV virulence, defined here as the rate of disease progression in untreatedinfections, is commonly estimated via the proxies of set point viral load (SPVL; theviral load after the resolution of acute infection but prior to AIDS), baselineCD4+ T-cell count (the first CD4 count after the resolution of acute infection),rate of CD4+ T-cell decline, level of immune activation, or viral replicativecapacity.