Herpes zoster-related hospitalizations and expenditures before and after introduction of the varicella vaccine in the United States

Abstract

Objective: With childhood varicella vaccination in the United States have come concerns that the incidence of herpes zoster may increase, because of diminishing natural exposure to varicella and consequent reactivation of latent varicella zoster virus. We wanted to estimate the rate of herpes zoster-related hospitalizations and the associated hospital charges before and during the promotion of varicella vaccination in the United States.

Design: A retrospective study of patients from the Nationwide Inpatient Sample for the years 1993-2004 who were hospitalized due to herpes zoster infection.

Methods: We searched for diagnoses of herpes zoster (using the International Classification of Diseases, Ninth Revision, Clinical Modification codes starting with 053) in all 15 diagnostic-code fields included for hospital discharges in the Nationwide Inpatient Sample during 1993-2004. We designed our analysis to examine the rates of severe illness due to herpes zoster that resulted in hospitalization, as measured by the rates of herpes zoster-related hospital discharges (HZHDs). The annual population-adjusted rate of HZHDs (per 10,000 US population) and the annual inflation-adjusted total charges for HZHDs were the primary outcomes. Secondary outcomes included mean charges for HZHDs and the distribution of total charges for HZHDs by expected primary payer. Varicella-related hospital discharges (VRHDs) were identified by use of similar diagnosis-based methods, which were described in our previous study.

Results: Population-adjusted rates of HZHDs did not change significantly from the prevaccination years (1993-1995) through the initial 5 years of the varicella vaccination period. Beginning in 2001, however, the rate of HZHDs overall began to increase, and by 2004 the overall rate was 2.5 HZHDs (95% confidence interval, 2.38-2.62) per 10,000 US population, significantly higher than any of the rates calculated during the years prior to 2002. Hospital charges for HZHDs overall increased by more than $700 million annually by 2004; in particular, we found that the herpes zoster vaccine-eligible population (ie, persons aged 60 years or older) accounted for 74% of the total annual hospital charges in 2004. The annual rate of VRHDs and the associated hospital charges decreased significantly from 1993 through 2004, but the decrease in hospitalizations and charges for VRHDs was less than the increase in hospitalizations and charges for HZHDs.

Conclusions: As the rates of VRHDs and the associated charges have decreased, there has been a significant increase in HZHDs and associated charges, disproportionately among older adults. Herpes zoster vaccine may mitigate these trends for HZHDs.