Combining HIV and AIDS surveillance: an experience from an Italian region

Surveillance systems based on the reporting of AIDS cases do not provide a completely up to date picture of the trend of the HIV epidemic, stressing the need for systems based on the diagnosis of HIV infection. However, implementation of these systems has been hindered by low feasibility, poor access to HIV testing, and problems related to confidentiality. The advantages and disadvantages of the two systems and of combined use were explored by comparing and integrating information from AIDS and HIV testing registries in a region of Northern Italy.

Linkage of AIDS and HIV testing registries allowed the annual number of incident and prevalent infections to be calculated. For linked cases, concordance of exposure category was determined.

Up to the end of 1995, 2186 AIDS cases and 5306 HIV-positive individuals were diagnosed. Linkage identified 1212 individuals reported to both registries. From 1990 to 1995, annual AIDS incidence steadily increased, while incidence of new HIV diagnoses decreased. The AIDS-to-AIDS-free ratio among those infected decreased from 1:5.6 in 1989 to 1:4.2 in 1995. The proportion of women and noninjecting drug users was higher among AIDS-free cases than among AIDS cases. The concordance of the exposure category was high (K = 0.70; 95% CI: 0.67-0.74), but it varied by exposure category; the highest concordance was for injecting drug users.

Integrated use of the information provided by these surveillance systems allowed us to better understand and foresee the AIDS epidemic dynamics. The data also suggested that the reliability of information on exposure category may vary among categories.