To the Editor.
—The incidence of hepatitis B virus (HBV) infection has been proposed as a marker for syringe sharing and human immunodeficiency virus transmission among injecting drug users. Pierce County, Washington, which includes Tacoma, is one of four sentinel counties in a national hepatitis surveillance system. The sentinel surveillance system is characterized by reliable reporting of HBV incidence and standardized determination of risk behaviors for HBV.1 Tacoma is also the location of the first syringe exchange program in North America; its operations are described elsewhere.2 Currently, an estimated 500 drug injectors exchange 2000 syringes each week in five Pierce County exchange locations. There are approximately 3000 drug injectors in the county; the syringe exchange program provides a means for safer injection for a substantial proportion of drug users. Syringe exchange users report a mean of three to four injections per day and are probably among the most