The burden and cost of hospitalised varicella and zoster in Australian children.

BACKGROUND: Economic analyses of varicella-zoster virus (VZV) immunisation are sensitive to the costs of hospitalised cases, so there is a need to validate VZV hospitalisation data. AIMS: To assess the accuracy of hospital VZV coding data and to apply these parameters to a population-based sample to estimate incidence and costs.
METHODS: A 3-year retrospective chart review from one hospital to document clinical features and validate coding data. A separate 9-year analysis of discharge data from two hospitals draining a defined region of suburban Melbourne, with adjustment for miscoding and estimates of direct hospital costs.
RESULTS: After correction for miscoding, 224 patients were admitted to one hospital over 3 years, 79% with varicella and 21% with zoster. Miscoding resulted in a 15% underestimate of zoster cases and a 4% overestimate of varicella cases. Thirty-six percent of varicella admissions compared to 80% of zoster admissions were immunocompromised and/or had chronic disease. Compared to otherwise-healthy patients, immunocompromised patients were admitted earlier in their illness and had lower complication rates. Forty-two percent of immunocompromised/chronic disease patients with varicella had a known exposure, usually from a family member. The incidence of hospitalised varicella and zoster in under 15-year olds was 15.7 and 1.8 per 100,000 per year, respectively. This suggests that there are 615 varicella hospitalisations and 72 zoster hospitalisations in this age group each year in Australia, at a total direct cost of over 2.2 million AU dollars.
CONCLUSION: These results highlight the considerable burden of hospitalised zoster and the importance of immunising non-immune contacts of immunocompromised individuals. They also support previous estimates of the incidence of hospitalised varicella in Australian children and adolescents, although direct medical costs may be higher than those previously estimated.