Prolonged nosocomial outbreak of hepatitis A arising from an alcoholic with pneumonia

From April to June 1996, an outbreak of hepatitis A virus (HAV) infection affecting 15 nurses, patients and household contacts occurred in the Department of Internal Medicine at Aker University Hospital, Oslo. The index case was a homeless alcoholic who was hospitalized in March 1996 with pneumonia while simultaneously incubating HAV infection. Four secondary cases were infected by the index case, while another 10 cases were caused by a continuous spread of infection within the department during the following months. Sequence of the VP1/P2A junction of HAV was obtained from 9 patients, including the index case, and all sequences were identical to each other. Mass vaccination of hospital employees with a formalin-inactivated HAV-vaccine took place in late May, and following this the outbreak stopped. Several factors probably combined to account for this unusual outbreak, e.g. an index case unsuspected of incubating with HAV infection, and a low prevalence rate of protective antibodies to HAV among the hospital staff.