PREVALENCE OF HIV-INFECTION IN FRANCE BEF ORE THE INTRODUCTION OF EARLY THERAPY - ESTIMATION BY BACKCALCULATION

In order to estimate the cumulative number of adults infected with Hum an Immunodeficiency Virus (HIV) in France, the method of <<backcalcula tion>> was applied. This method assumes that the incubation period is constant over time, but the therapies administered since May 1987 amon g Acquired Immunodeficiency Syndrome (AIDS)-free HIV seropositive, ext end the incubation period. It is obvious that if AIDS incidence counts beyond June 1987 are included in the backcalculation, this may lead t o underestimation of the number of HlV infected subjects. For this rea son we focused our study on estimates obtained from AIDS cases diagnos ed until June 30, 1987. For each estimate we made the hypothesis of an average incubation time of 11 years (i.e. period between time of infe ction and onset of AIDS). We also examined the sensitivity of the resu lts, with distributions of average incubation periods of 9 to 13 years . A <<plausible range>> (PR) was systematically calculated: it takes i nto account the imprecisions arising from model adjustment and from un certainties regarding distribution of incubation period. Thus, the tot al number of infected people in France up to June 30, 1987, was estima ted at 142,300 (PR : 82,200 to 240,600), corresponding to art infectio n rate of 0.42 (PR : 0.24% to 0.71%) for the population between 15 and 59 years of age. Estimations were also calculated according to sex fo r some transmission groups: homosexuals, injecting drug users and hete rosexuals.