Comparing shingles incidence and complication rates from medical record review and administrative database estimates: how close are they?

Accurate rates of herpes zoster incidence and complication have become of greater interest as studies have suggested an increasing temporal trend in incidence rates across all age groups and long-term follow-up studies of vaccine effectiveness are required by the Food and Drug Administration. This study compares the results obtained from the most commonly used method to obtain herpes zoster data (rates obtained from administrative data) with results obtained when administrative data are supplemented by medical record review. Administrative billing code data identified 1,959 cases of herpes zoster in Olmsted County, Minnesota, adults between January 1, 1996, and December 31, 2001. Of those 1,959 cases, 1,669 (85.2%) could be confirmed by medical record review, a decrease in incidence rate of 14.8%, resulting in a decrease of 0.61/1,000 person-years when adjusted to the US adult population. Complication rates were also significantly different between the 2 methods. It is not clear if the 15% decrease in incidence rates would be seen in every administrative data set or if the lack of confirmation of cases may be variable in both validity and reproducibility between data sets, making estimations in temporal trends and pre/post-vaccine rates difficult to compare across data resources.