BACKGROUND:
Varicella vaccine was licensed by the FDA in 1995. It was expected that widespread vaccine use would reduce total disease incidence, as well as the incidence of severe disease. According to the 2002 National Immunization Survey, 70% of Indiana children 19-36 months of age have had one dose of varicella vaccine. Hospital discharge data, which could be used as a source to monitor severe disease, is available to the Indiana State Department of Health for the years 1994-2002.

OBJECTIVE:
To monitor changes in the epidemiology of severe cases of varicella resulting in hospitalization, with emphasis on age group trends.

METHOD:
Analysis of Indiana Hospital Discharge Data was conducted from years 1994-2002. The analysis focused on age group incidence to identify shifts in the burden of severe disease.

RESULT:
For the nine years for which data is available, the mean number of hospitalizations due to varicella was 229. From 1994-1998, the mean number of hospitalizations was 275, and the mean number of hospitalizations for 1999-2002 was 151, a reduction of 45%. From 1994 to 2002, the 1-4 year age group experienced a 51% decline (from 33.2% of all cases to 16.3%) in percent of hospitalized cases due to varicella. The 30+ year age group had a 62% increase (from 16.3% of all cases to 26.4% of cases) in hospitalizations, the largest percentage increase of any age group.

CONCLUSION:
As expected, the burden of severe varicella disease resulting in hospitalization appears to be decreasing. In addition, a shift in the percentage of hospitalizations among various age groups also seems to be occurring. The age group most likely to be vaccinated (1-4 years) showed a decrease in the percentage of hospitalization, while an increase in the percentage of hospitalizations in adults 30 years and older occurred.

LEARNING OBJECTIVES:
Severe illness from varicella resulting in hospitalization can be monitored by using hospital discharge data.