Longer survival after HIV infection for injecting drug users than for homosexual men: implications for immunology

Background: Comparisons of progression in HIV‐1 infection between injecting drug users (IDU) and homosexual men have been inconclusive due to short follow‐up periods, often with less well‐defined starting points and endpoints. In addition, comparisons of survival after infection have been to some extent obscured by higher non‐AIDS mortality in IDU. Methods: In a retrospective cohort study, homo‐/bisexual men and IDU were followed, with dates of seroconversion defined within ± 1 year by a previously negative HIV antibody test. Endpoints were CD4 cell count below 200 × 106/l, AIDS, and death from AIDS. Results: Sixty‐three homo‐/bisexual men and 125 IDU fulfilled the entry criteria, with no significant differences in age at or date for seroconversion. Mean follow‐up times were 6.7 and 7.0 years, respectively. The homo‐/bisexual group had a significantly accelerated progression rate to all three endpoints: time to CD4 cell count below 200 × 106/l (P= 0.002), to AIDS (P = 0.0003), and to death from AIDS (P < 0.0001). Adjusting for age and sex only made marginal alterations. Ten years after infection, 54% of homosexual men had developed an AIDS‐defining condition and 51% had died from AIDS, whereas the corresponding percentages in the IDU group were 26 and 15%, respectively. There was, however, no difference in overall mortality due to an almost constant, non HIV‐related, yearly mortality of some 4% in IDU. Conclusions: In our cohort there was a highly significant difference in disease progression and death from AIDS between homo‐/bisexual men and IDU. This difference was proposed to be due to the transmission route determining the initial immune response and suggested that this route may have played a more important role than virus variability on the subsequent prognosis.