Annual incidence rates of herpes zoster among an immunocompetent population in the United States

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Abstract
Herpes zoster (HZ), also known as shingles, is a painful and commonly occurring condition in the United States. In spite of a universally recommended vaccine for use in immunocompetent adults aged 60 years and older, HZ continues to impact the American public, and a better understanding of its current incidence is needed. The objective of the current study is to estimate the overall and age- and gender-specific incidence rates (IRs) of HZ among an immunocompetent US population in 2011 following availability of a vaccine. Claims data from the Truven Health MarketScan® Research databases between 01/01/2011 and 12/31/2011 were extracted. Immunocompetent adult patients, enrolled as of January 1, 2011 were analyzed. The denominator was defined as eligible subjects who were immunocompetent, had no evidence of zoster vaccination, and no diagnosis of HZ (International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis code 053.xx) in the 90 days prior to January 1, 2011. Subjects contributed person-days to the denominator until the occurrence of one of the following events: end of continuous enrollment in the database, a claim for zoster vaccination, diagnosis of HZ or end of the observation period (December 31, 2011). The numerator was defined as enrollees within the denominator file exhibiting evidence of HZ. Annual IRs were calculated for the entire population in the database as well as by gender and age group; standardized IRs were also produced using the 2010 US Census data. The overall annual IR of HZ across all ages was 4.47 per 1000 person-years (95 % confidence interval [CI]: 4.44–4.50) which monotonically increased with age from 0.86 (95 % CI: 0.84–0.88) for those aged ≤19 to 12.78 (95 % CI: 12.49–13.07) for patients ≥80 years. The IR was 8.46 (95 % CI: 8.39–8.52) among adults ≥50 years and 10.46 (95 % CI: 10.35–10.56) among those aged ≥60 years. Women compared to men had higher HZ incidence (5.25, 95 % CI: 5.21–5.29 vs. 3.66, 95 % CI: 3.62–3.69) and this was seen across all age groups. When adjusted for age and gender using 2010 US Census data, the annual IR was 4.63 per 1000 person-years (95 % CI: 4.61–4.66). Despite the availability of a vaccine, HZ remains common among immunocompetent adults in the US with incidence rates of HZ observed to increase with age and be higher in women than men.