Chronic medical conditions as risk factors for herpes zoster.

To determine the degree to which chronic conditions might contribute to the unexplained burden of herpes zoster.We conducted a case-control study using MarketScan data from January 1, 2007, through December 31, 2007, to investigate chronic conditions as risk factors for herpes zoster among persons 20 to 64 years old. Cases were enrollees with a herpes zoster diagnosis (International Classification of Diseases, Ninth Revision, Clinical Modification codes 053.xx), and controls were those without a herpes zoster diagnosis, matched by age groups and insurance plan. We selected 10 chronic conditions based on their prevalence in the general population. We calculated the attributable fraction and created a comorbidity composite score by summing the significant coefficient of regression of chronic conditions. We used logistic regression to evaluate the associations between herpes zoster and chronic conditions.We identified a total of 59,173 cases and 616,177 controls for the analysis. Risk of herpes zoster was significant for 8 of the 10 study conditions (odds ratios, 1.06-1.52). Herpes zoster risk also increased as a function of comorbidity composite score. The attributable fractions for these 8 significant conditions ranged from 0.24% to 2.89%.The risk of herpes zoster may be increased in people with chronic conditions. However, this risk may not contribute substantially to the burden of herpes zoster in the population. The causes for most cases of herpes zoster remain unknown.