Back-calculation and projection of the HIV/AIDS epidemic among homosexual/bisexual men in three European countries: Evalution of past projections and updates allowing for treatment effects

Abstract

This study critically evaluates the quality of 1990 back-calculations and long-term projections of the HIV/AIDS epidemic for homosexual/bisexual men in France, the Federal Republic of Germany, and the UK. The projection captured the general pattern observed in all three countries although the observed AIDS incidence peaked 2–3 years later and declined faster than had been projected. Total AIDS incidences from 1989 to 2000 were overestimated by 38.5% in France, and underestimated by 23.9 and 17.5% in western Germany and the UK. Updated back-calculations and projections to 2020 use AIDS incidence data up to 2000. The procedure incorporates an asymmetric long-tailed cumulative HIV curve as well as the increase in the median incubation period brought about by new therapies introduced during the 1990s. The results suggest that: (i) The rapid decrease in cases during the late 1990s was caused by a median incubation period that increased from 10 years to 21–23 years by the late 1990s. (ii) An imminent bottoming out followed by a protracted increase in AIDS cases from 2000 to at least 2010 could be the consequence of a leveling off of the median incubation period. (iii) A low variant of the projections shows that at least 40,000 homosexual men could develop AIDS in the three countries after 2000.