The participants did not differ significantly from those excluded from the longitudinal study regarding age, lifetime and recent number of partners (p value from t-test > 0.05 for all the comparisons, data not shown), and also regarding partnership, history of sexually transmitted infections, smoking status and HIV-related parameters (i.e., HIV-1 RNA, nadir and current CD4 + T-cell counts) (Fisher exact p value > 0.05 for all the comparisons, data not shown). This evidence concerns the gene CD4 and sexually transmitted disease.