HIV infection in children is predominantly acquired perinatally and differs from disease in adults in its clinical presentation and disease progression.

There are marked age dependent differences in the profile of T lymphocyte subsets in children. In infancy, CD4 cell counts are generally higher than adult levels and attain adult levels by the age of 6 years. Unlike the absolute CD4 cell counts where the levels specifying immune suppression changes with age, the CD4 percentage specifying immune suppression does not change with age and is therefore a more useful marker for identifying disease progression in children. Infants with CD4 percentage of 15-25% are considered moderately immune suppressed and those with percentage CD4 levels < 15% are considered severely immune suppressed.

Regarding the use of viral load to guide therapy it is worth noting that perinatally infected infants have high plasma viral loads within the first 2 months of life. This is followed by a slow decline in the first few years of live. The level of HIV RNA considered indicative of increased risk for disease progression is not well defined for young children and will have to be reviewed as more data becomes available.

Treatment guidelines for children will therefore have to take these differences into account although they follow the same principles as in adults.