Viral burden in peripheral blood can be determined by using quantitative HIV RNA assays. During the period of primary infection in adults, HIV RNA copy number initially rises to high peak levels. Coincident with the body's humoral and cell-mediated immune response, RNA levels decline by as much as 2–3 log10 copies to reach a stable lower level (i.e., the virologic setpoint) approximately six to twelve months following acute infection, reflecting the balance between ongoing viral production and immune elimination (31, 32). Several studies conducted among adults have indicated that infected persons with lower HIV copy number at the time of RNA stabilization have slower progression and improved survival compared with those with high HIV RNA set points (33, 34).
On the basis of such data, recommendations for the use of HIV RNA copy number in deciding to initiate and change antiretroviral therapy in infected adults have been developed (5). These recommendations also are applicable to infected adolescents, particularly those who have acquired HIV infection recently rather than through perinatal infection.
Inherent biologic variability must be considered when interpreting changes in RNA copy number in children. Thus, only changes greater than five fold (0.7 log10) in infants aged <2 years and greater than three fold (0.5 log10) in children aged 2 years after repeated testing should be viewed as reflecting a biologically and clinically significant change.