Hepatitis A in Mauritius: an apparent transition from endemic to epidemic transmission patterns.

Between January 1984 and December 1985 a large outbreak of viral hepatitis occurred in the island nation of Mauritius (population 986,000). No hepatitis epidemics had occurred there since the 1930s. The outbreak involved 2428 reported cases; however, reporting levels were thought to be extremely low. All of the island's nine geographical districts were affected, but cases were concentrated in five districts mostly in the central and northern parts of the island. The highest attack rate occurred in children aged five to nine; persons above age 14 were almost unaffected. The male:female ratio of cases was 1.1:1. Evidence to support hepatitis A virus (HAV) as the infecting agent included; (1) clinical illness was compatible with hepatitis A; (2) the age profile of cases was typical for community-wide hepatitis A outbreaks; (3) the rate of positive tests for hepatitis B surface antigen in suspected hepatitis patients did not increase during the outbreak; and (4) nine of nine clinically ill children tested were serum-positive for IgM anti-hepatitis A virus antibody. Transmission was probably by the person-to-person route; no common source was implicated. The outbreak appears to represent a transition from a 40-year pattern of endemic HAV transmission on the island to an epidemic pattern.