Laboratory-based HIV surveillance with information on exposure: importance of discriminating person-based from test-based results.

Within a surveillance programme in a Regional Public Health Laboratory anonymous information on HIV test, requesting physician and tested individual is automatically selected, regardless of test result. Thereby, personal identifiers are transformed into unique but meaningless numeric codes. Besides, requesting physicians receive a questionnaire on indication for testing (response 87%). Between April 1989 and June 1993 12,219 HIV tests were performed in 10,972 individuals. The percentage of positive tests (2.1%) was twice the percentage of positive individuals (1%). No increase in number of new infections was observed over time. Of individuals, 41.6% were tested due to third party requests (mainly insurance): HIV was demonstrated once (0.03%). Among the remainder, with medical indications, seroprevalence was 1.4%. At relatively little expense, we were able to provide valid information about patterns of HIV-testing and HIV seroprevalences among people tested in routine medical practice. Prevention of double counts proved to be important. Extension to other Dutch areas is expected.