Behavioural changes in intravenous drug users in Geneva: rise and fall of HIV infection, 1980-1989.

In the early 1980s, more than 90% of intravenous drug users (IVDUs) shared needles and syringes in Geneva. The prevalence of antibodies to HIV in the sera of outpatient IVDUs increased from 6% in 1981 to 38% in 1983; it was, however, still only 37% in 1988. IVDUs starting methadone maintenance in 1987-1989 had a seroprevalence rate of 22%. In 1989 the percentage of IVDUs exchanging syringes and needles fell to only 5% of seropositive addicts. Only one seroconversion was observed in 1094 patient-months of observation in 1988-1989, which was probably due to sexual contact. The evidence suggests that, in the IDVUs studied, transmission of HIV has diminished since the early 1980s.