Investigation of an outbreak of hepatitis A simplified by salivary antibody testing.

In March 1988 a general practitioner notified two cases of hepatitis A in a private boarding school. Epidemiological investigation, including testing for salivary antibodies revealed a further five cases and established immunity to, and recent infection with, hepatitis A virus (HAV). The pattern of the outbreak was described. A number of practices which would encourage cross-infection were corrected. Normal human immunoglobulin was given to contacts. Repeat salivary testing 10 weeks later revealed that two more boys had become reactive for anti-HAV, though at a low titre. These may have been serological responses to HAV infection modified by the passive immunization.