Contagiousness of acute hepatitis B. Secondary attack rates in household contacts.

In order to define the hazard of household exposure to patients with acute hepatitis B, in the absence of persistent hepatitis B surface antigen (HBSAg), 98 household contacts of 42 patients with the acute disease were interviewed and tested for HBSAg, antibody to HBSAg (anti-HBS), and serum transaminases shortly after identification and at 3-month intervals for at least 12 months. Most of the index cases with acute hepatitis B were young men and many had used illicit drugs parenterally before the onset of illness. Three of the household contacts had HBSAg detected on initial testing, and 2 of these were carriers with elevated serum transaminase levels. The 3rd HBSAg-positive contact developed acute hepatitis within 2 weeks. This appeared to represent a coprimary infection. Fourteen contacts had anti-HBS on initial evaluation and were considered immune as a result of prior experience with hepatitis B. Of 81 susceptible contacts (neither HBSAg nor anti-HBS on initial screening), 13 were spouses or sexual partners and 2 of these developed acute hepatitis B at 4 and 6 months after the onset of illness in their respective index cases; another developed anti-HBS at 6 months. Thus, 3 (23%) of 13 exposed spouses or sexual partners developed evidence of hepatitis B infection during the surveillance period. In contrast, no evidence of hepatitis B infection related to household exposure was found in 68 parents, siblings, and other domestic contacts. These data confirm the contagiousness of hepatitis B for household contacts of acute cases and suggest that the risk is confined to spouses and sexual partners. These persons appear to be prime candidates for prophylaxis with hepatitis B immune globulin.