Recent trends in the HIV epidemic among injecting drug users in Northern Italy, 1993-1999

Objective: To monitor and describe the time trends of the HIV epidemic amon g intravenous drug users (IDU) attending drug dependence treatment centres (DDTC) in Northern Italy. Design: A cohort of all seronegative IDU attending DDTC in Lombardy between 1993 and 1999; all had been tested for HIV at least twice. Periodic sample interview surveys were done to assess risk behaviours. Methods: The incidence rates of HIV infection were calculated using the per son-year (PY) method and expressed as the number of cases per 1000 PY at ri sk. Background HIV prevalence was calculated by dividing the number of posi tive cases by the total number of IDU tested at all DDTC in Lombardy. Results: Between 1993 arid 1999, 135 seroconversions occurred in 7945 subje cts followed for 19 671 PY yielding an incidence rate of 6.9/1000 PY. Ninet y seroconversions occurred among the 6563 males and 45 seroconversions amon g 1382 females (incidence rates 5.5 and 14.0, respectively). Among the male s, the incidence of HIV was 4.5 in those aged less than 25 years and 5.8 in those aged 25 years or more. Among the females, the corresponding figures were 21.1 and 10.3. HIV prevalence decreased over time, and it was higher a mong females. Sexual behaviours at risk were more common among females. Conclusions: The incidence of HIV infection among IDU in Northern Italy was stable between 1993 and 1999. The higher incidence and prevalence among fe males and the different prevalence of risk behaviours between genders sugge st an increasing role of heterosexual transmission. (C) 2001 Lippincott Wil liams & Wilkins.