Predictors of positivity for hepatitis B and the derivation of a selective screening rule in a Canadian sexually transmitted disease clinic.

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To determine the prevalence of hepatitis B surface antibody (anti-HBs) and antigenemia (HBsAg), the risk factors for seropositivity and the effectiveness of a selective serologic screening rule among sexually transmitted diseases (STD) clinic attendees. Clients in the Hamilton STD Clinic were surveyed from October 1992 to July 1993 on sociodemographic, past medical, and behavioural data, were tested for several STDs and were offered serological testing and vaccination against hepatitis B. Predictors of seropositivity were determined by single variable analysis. A selective serologic screening rule was derived using logistic regression modelling. The seroprevalence of anti-HBs was 6.8% (21/310) in the 310 of 385 clients (80.5%) who agreed to be tested and interviewed. There were no HBsAg carriers. Five independent risk factors were identified by logistic regression: (1) age greater than 35 years; (2) birth outside Canada and histories of; (3) syphilis; (4) gonorrhoea; or (5) injection drug use. If clients with at least one of these predictors had been tested, 34.5% would have been selected for serologic testing and 85.7% of all positives would have been detected. The screening rule was more effective for men than for women. In this low prevalence setting, selecting STD clinic clients based on the presence of any one of five risk predictors appears to be an effective strategy for hepatitis B serologic screening in the context of a Canadian vaccination program.