Intensive hepatitis surveillance in Minnesota: methods and results

After a large foodborne outbreak of hepatitis A in April 1974, the Minnesota Department of Health attempted to improve ongoing hepatitis surveillance with a system based on 1) a large centralized blood bank, which reports results of tests for hepatitis B surface antigen (HBsAg) on suspected hepatitis patients; 2) private physicians, who are encouraged to report cases; and 3) an epidemiology aide, who contacts all detected patients and their physicians. During the first year of this system, we detected 932 cases (24.5 per 100,000), a threefold increase over previous years, and obtained detailed epidemiologic data on each case. Although physicians diagnosed 61% of these cases as hepatitis A (or non-B) and 39% as hepatitis B, they tested only 53% of all patients for HBsAg. Sixty-seven per cent of the tested patients were HBsAg-positive, but only 17% of the untested patients had illnesses diagnosed by physicians as hepatitis B. This suggests that many patients with clinically-diagnosed viral hepatitis who are not tested for HBsAg may be erroneously diagnosed by physicians as having non-B hepatitis. Thirty-three per cent of HBsAg-positive patients with known occupations, not including housewives and students, worked in meidcally-related occupations. For 51% of the HBsAg-positive patients, we could not identify recent parenteral exposure to hepatitis B.