[Virological diagnosis of HIV infection in children].

The laboratory diagnosis of HIV-1 infection in newborns should be carried out using virological methods, viral isolation or molecular methods for the detection of proviral DNA by PCR. Serological methods have poor sensitivity in the first months of life because the IgG of the seropositive mother crosses the placenta. Once HIV-1 infection is diagnosed, other assays are available which indicate the clinical progression of the infection, the genetic variability of the virus, its biological behavior and sensitivity to different antiretroviral medications. These studies can be used independently of the clinical manifestations in order to assess disease progression. Different immunological markers and virological markers of disease progression have been described, but the CD4+ T lymphocyte count is used routinely as an immunological marker and as a virological marker of the virus load. In HIV-1 newborns and children, the largest decrease in the number of CD4+ T lymphocytes is due to the combined effect of infection progression and a natural decrease in CD4+ T lymphocytes with age. In newborns, low viral load levels suggest that the infection was acquired shortly before birth or that maternal and/or placental factors inhibited viral replication before birth, or that the child was infected at birth. In children, viral loads are greater than in adult patients during the primary infection and throughout their evolution. Because of advances in the treatment of HIV-1 infection, the study of resistance to antiretroviral agents by phenotypical and genotypical methods is important. Increased viral load suggests the loss of effectiveness of a treatment and should be monitored.