In one study of post-partum women, the rate of misclassification was not associated with age or CD4 cell count (although there were low numbers of women with the lowest CD4 counts) [14], but this is not necessarily inconsistent with an up-turn in PFP many years after infection (fertility declines steeply with time infected with HIV [27], and most women in this study would probably have been infected in the previous few years). The gene discussed is CD4; the disease is infection.