Efficacy of immune serum globulin in an outbreak of hepatitis A virus infection in adults.

While immune serum globulin has been shown to be highly effective in preventing hepatitis A infection when administered before exposure to the virus, its efficacy when given after exposure is less clear. Timing of administration appears critical and the question of whether it modifies the clinical manifestations of the disease with possible asymptomatic seroconversion has not been conclusively answered. These aspects were examined in a common-source outbreak of 19 cases of hepatitis A in a military unit. Immune serum globulin administered between 2 and 3 weeks after suspected exposure to the virus did not modify clinical manifestations of the disease. Furthermore, in a subgroup studied serologically, there were eight clinical cases and only one case of asymptomatic seroconversion. Thus, late administration of immune serum globulin appears to have little effect on the clinical course of hepatitis A infection and does not appear to result in any significant degree of active-passive immunity.