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Estimating the cumulative number of human immunodeficiency virus diagnoses by cross-linking from four different sources.

BACKGROUND
We estimated the cumulative number of people diagnosed with human immunodeficiency virus (HIV) infection in a region of Italy by cross-linking data from four surveillance systems and applying capture-recapture methods.


METHODS
The study was conducted using data referring to residents of the Veneto Region (population 4.4 million). We cross-linked data from the AIDS Registry (data 1983-2000), the HIV Registry (1988-2000), the Death Registry (1992-1999), and the Hospital-Discharge Registry (1997-2000), using a code based on name, birth date, and sex. A specific software for capture-recapture models (CARE-1) was used to estimate the size of the target population with two different statistical approaches (sample coverage and log-linear models).


RESULTS
A total of 2801 people were reported to the AIDS Registry, 6415 to the HIV Registry, 1598 to the Death Registry as HIV/AIDS-related deaths, and 3330 to the Hospital-Discharge Registry with a diagnosis of HIV infection. Overall, 8723 people were present in at least one registry: 4896 people were present in only one registry, 2387 in two registries, 1286 in three registries, and 154 in all four registries. Using the sample coverage approach, we estimated that, since the beginning of the epidemic in Veneto, an estimated 11 281 people (95% CI: 10 981, 11 621) should have been reported to at least one registry; thus the estimated coverage of the four registries was 77.3% (i.e. 8723/11 281). Results obtained applying the log-linear approach were similar, although the fitting of this model was not adequate.


CONCLUSIONS
Cross-linking data from four different sources and applying the capture-recapture method can improve the accuracy of the estimates of the dimensions of the HIV epidemic.