Including pre-AIDS mortality in back-calculation model to estimate HIV prevalence in France, 2000

Since the advent of highly active antiretroviral therapy (HAART) the lengthening of AIDS incubation time has led to a decrease of AIDS incidence and mortality, and to the increase of the proportion of pre-AIDS mortality. The objective was to develop an extension of the back-calculation model by including pre-AIDS mortality and to estimate HIV prevalence in France. Our previous back-calculation model was modified to take into account the probability of survival for HIV-infected individual using the relative risk to die at different period for an HIV-infected person versus the general population (psi). AIDS cases reported to InVS (Institut de Veille Sanitaire) until March 2003 were back-calculated to estimate HIV incidence until December 2000. AIDS deaths occurring until December 2000 were used to obtain HIV prevalence in 2000. Plausible intervals were calculated taking into account uncertainties on AIDS incubation time. Taking into account pre-AIDS mortality increased the goodness-of-fit of the model to the data. The relative risk, psi, was estimated as 3 for homo-bisexual men, haemophiliacs and transfused cases, 10 for intravenous drug users, and 4 for heterosexual cases, with no difference over period. HIV prevalence in 2000 was estimated as 88,200 (with a plausible interval of 52,300-168,000), versus 78,200 when mortality was not considered. Pre-AIDS mortality estimates show the amount of this mortality during the era of HAART but also evidenced its existence before HAART. Taking into account pre-AIDS mortality of HIV-infected person in the back-calculation model increased the estimated HIV prevalence.