To describe the epidemiology of infection with the human immunodeficiency virus type 1 (HIV-1) in Victoria from 1980 to 1991.

Data on HIV-1 infection in Victoria, obtained through routine laboratory-based surveillance, were entered in a database. Missing information was sought by contacting the referring doctor where possible.

In Victoria, the acquired immunodeficiency syndrome (AIDS) is notifiable to Health Department Victoria by diagnosing doctors, and laboratories are required to notify new diagnoses of HIV-1 infection, without identifiers. All confirmatory testing for HIV-1 has taken place at the State HIV Reference Laboratory at Fairfield Hospital.

Diagnoses of HIV-1 infection, as confirmed at the State HIV Reference Laboratory by western blot immunoassay, and notifications of AIDS to Health Department Victoria.

Over six years the annual number of diagnoses of HIV-1 infection in Victoria remained constant despite a substantial increase in the number of tests performed. To the end of 1991, 2679 people had been diagnosed with HIV-1 infection, 686 of whom had developed AIDS. Information on exposure was available for 2379 (88.8%). Homosexual and bisexual men made up 75.5% (85.0% of those for whom exposure had been ascertained); 3.4% were female or heterosexual male injecting drug users; and 3.7% were heterosexuals with no history of injecting drug use. The latter two groups contributed 2.0% in 1985 to the proportion of all new diagnoses for which exposure was known, and 14.3% in 1991; for recipients of contaminated blood or blood products before 1985 this proportion fell from 12.4% to 1.0%. The cumulative incidence of HIV-1 diagnoses was highest in the age group 25-29 years, and 20% of all HIV-1 infected people were under 25 at the time of diagnosis. In 1991, 81 of the 311 people who had been diagnosed with HIV-1 infection had had previous negative or indeterminate results of tests; half of these had acquired infection in the previous year.

Most HIV-1 infections in Victoria have been acquired through male homosexual contact, with a small but increasing proportion of diagnoses occurring in heterosexuals. Laboratory-based surveillance of voluntary testing, despite its limitations, has provided valuable information on the extent of the HIV-1 epidemic in Victoria. Surveillance of all HIV-1 test results and of seroconverters now supplements routine surveillance of HIV diagnoses and will ensure a more accurate picture of the epidemic in coming years.