Level and pattern of HIV-1-RNA viral load over age: differences between girls and boys?

To estimate RNA viral load patterns over age in vertically infected children that account for between- and within-individual variation, treatment and assay cut-off detection level. To investigate possible sex-based differences.

A total of 118 infected children with 894 RNA viral load measurements enrolled in the European Collaborative Study were prospectively followed from birth for up to 15 years.

Fractional polynomial and mixed effects models with censored data to assess the non-linear pattern of viral load over age, allowing for repeated measures.

The RNA viral load peaked at approximately 3 months of age, and gradually declined thereafter. The sex by age interaction was significant (chi2 = 19.7, P < 0.001); viral load peaked higher for girls than boys, but after 4 years the RNA load was consistently 0.25-0.5 log10 lower for girls than boys. The effects of sex and treatment on viral load vary over age (chi2 = 6.31, P = 0.043). Sex differences in RNA viral load relating to measurement without treatment were more pronounced than those under treatment. Disease progression was more rapid for girls than for boys up to the age of 4 years, and less rapid thereafter; the overall difference was not statistically significant.

Differences in RNA viral load over age between untreated boys and girls may have implications for policies for the initiation of antiretroviral therapy, but do not seem to translate into differences in progression to serious disease. The findings would suggest underlying biological explanations, which need further investigation.