Immunoglobulin M-specific serologic testing in an outbreak of foodborne viral hepatitis, type A.

Ninety-seven symptomatic and five asymptomatic infections with viral hepatitis, type A (102 cases) were identified in members, guests and employees of a private country club in an outbreak associated with consuming food and ice prepared or handled by an employee of the club's kitchen pantry. Twenty-three symptomatic persons were tested by differential radioimmunoassay for immunoglobulin M (IgM) (acute-phase) hepatitis A antibody (anti-HAV) and all 23 were documented to be infected with hepatitis A virus (HAV). Forty-one member/guest cases had only a single exposure at the county club. Their incubation periods ranged from 21 to 40 days, with a mean of 30 days. The exposure of these single-day patrons occurred over a 14-day period. The index case was not icteric and only moderately symptomatic and was diagnosed retrospectively to have viral hepatitis, type A by serologic determination of IgM anti-HAV in blood samples. Four items implicated in disease transmission were potato salad, hot dogs, molded salmon and ice handled by the index case. Serologic screening of controls did not appear to alter the conclusions of the food item analysis.