OBJECTIVE: To measure the HIV seroprevalence rate in a surrogate sample of the general population in the province of Quebec, using a network of sentinel hospitals. DESIGN: Anonymous unlinked sentinel surveillance study. SETTING: Outpatient surgery units in 19 acute care hospitals throughout Quebec. PARTICIPANTS: All patients attending the outpatient surgery units from November 1990 to October 1992. A total of 61,547 plasma samples were obtained from leftover blood samples collected for cell counts. Fifty samples were excluded because of an insufficient amount of plasma and one because of an indeterminate result. INTERVENTION: HIV antibody testing with enzyme-linked immunosorbent assay; positive results confirmed with radioimmunoprecipitation assay. OUTCOME MEASURES: HIV antibody status, sex, year of birth and area of residence. RESULTS: The crude seroprevalence rate among the subjects aged 15 years or more was 0.4 per 1000 population (95% confidence interval [CI] 0.2 to 0.7) among the women and 3.6 per 1000 population (95% CI 2.8 to 4.4) among the men (p < 0.001). The rate after adjustment for age, sex and geographic distribution of the study population was 2.3 per 1000 population (95% CI 1.9 to 2.7). The seroprevalence rate among the male patients in the City of Montreal was much higher than the rates elsewhere in the province. It increased progressively during each of the four 6-month intervals of the study: 8.1, 8.7, 13.9 and 18.3 per 1000 respectively (chi 2 linear trend = 4.76; p = 0.029). No similar trends were observed outside Montreal for the male patients. There were too few seropositive female patients to draw any solid conclusion. CONCLUSIONS: Despite the possible drawbacks of a nonrandomized sampling scheme, this study suggests that in the male population the HIV seroprevalence rate is increasing in Montreal and is stable in all other areas of the province. The continued surveillance of HIV infection through anonymous unlinked studies is useful to monitor trends.
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