Disease burden and epidemiological characteristics of varicella in Taiwan from 2000 to 2005

Background and purpose: Varicella has an important impact on public health, especially before the introduction of the varicella vaccine. This study investigated the epidemiological characteristics and disease burden of varicella during the introduction of the varicella vaccine for mass vaccination in Taiwan. Methods: The International Classification of Diseases, 9th Revision, Clinical Modification codes related to varicella (052, 052.1, 052.2, 052.7, 052.8, 052.9) were analyzed for the population of Taiwan from 2000 to 2005 through the National Health Insurance database. Results: Most of the patients with varicella were younger than 10 years. The overall age-specific annual incidence peaked in 4- and 5-year-old children (60.5 and 60.2/1000 children, respectively). A significant decrease in incidence among 3- to 6-year-old children was observed in areas with free varicella vaccination (p<0.001). Winter was the season for epidemic varicella, particularly January. The varicella-related hospital admission rate was 60/1000 patients (95% confidence interval [CI], 48.5-71.5/1000 patients). Infants younger than 1 year, and adults aged from 19 to 38 years and older than 75 years had the highest hospital admission rates. The mean duration of hospital stay was 5.05 days (95%CI, 4.98-5.12 days). The complication rate among patients admitted to hospital was 39.1%, and the most common complication was lower respiratory tract infection (22.1% among patients admitted to hospital). Twenty nine patients with varicella died; 52% had underlying disease and 72% had complications related to varicella. The annual varicella-related medical expense was highest in 2000 (NT$118.6 million/year) and declined after 2002. Conclusions: Most patients with varicella were younger than 10 years, and the incidence peaked among children aged 4 to 5 years. The incidence of varicella among 3- to 6-year-old children was significantly lower in the areas with a free public vaccination policy. The hospital admission rates were highest for infants and elderly people.