KEYWORD1:
Hepatitis A, Incidence, Surveillance

BACKGROUND:
When hepatitis A vaccine was licensed in 1995, disease incidence in California was 21 cases per 100,000, almost twice the national rate. In 1999, the vaccine was introduced into the California Childhood Immunization Schedule. Since the availability of the vaccine, the incidence of hepatitis A has declined dramatically in California.

OBJECTIVE:
To describe trends in hepatitis A incidence in California.

METHOD:
All hepatitis A cases reported to the State Notifiable Diseases Surveillance System between 1990 and 2001 were included in the analysis. Incidence rates were calculated using 1990/2000 census data and intercensal population estimates.

RESULT:
From 1990 to 1994, the average rate of hepatitis A was 18.6 per 100,000. Between 1995 and 2001, disease incidence declined 75% to 5.2 cases per 100,000. Rates have declined in all age and racial/ethnic groups. Rates among children under 19 years of age, declined from 16.3 to 1.2 per 100,000 among whites and from 40.3 to 8.9 per 100,000 among Hispanics. Rates among adults 19 years of age and older declined from 19.2 to 4.2 per 100,000 among whites and from 10.2 to 4.0 per 100,000 among Hispanics.

CONCLUSION:
Hepatitis A incidence in California is currently at an historic low. This may be the result of the introduction of hepatitis A vaccine into California during an interepidemic period when disease incidence was already on the decline. The California State Immunization Branch will continue to monitor trends in hepatitis A and examine available vaccination data to assess the role of hepatitis A vaccine on the decline in disease incidence in the state.

LEARNINGOBJECTIVES:
Describe the changes in hepatitis A incidence before and after the availability of hepatitis A vaccine in California.