Risk factors for herpes zoster in patients with rheumatic diseases: a nationwide cohort study in Korea

Objective. To determine the risk factors for herpes zoster (HZ) in patients with rheumatic diseases in Korea. Methods. We used the nationwide database of the Health Insurance Review & Assessment Service to analyse patients aged >20 years who had visited a hospital more than twice for rheumatic disease as a principal diagnosis from January 2009 to April 2013. HZ was identified using HZ-related Korean Standard Classification of Diseases 6 (KCD-6) codes and the prescription of antiviral agents. The relationship between demographics, comorbidities and medications and HZ risk was analysed by Cox proportional hazards models. Results. HZ developed in 1869 patients. In Cox proportional hazards models, female sex but not age showed an increased adjusted hazard ratio (HR) for HZ. Comorbidities such as haematologic malignancies, hypertension, diabetes mellitus, and chronic lung and liver diseases led to an increased HR. HZ risk was higher in patients with SLE (HR: 4.29, 95% CI: 3.49, 5.27) and Behcet's syndrome (BS, HR: 4.54; 95% CI: 3.66, 5.64) than with RA. The use of conventional DMARDs, immunosuppressants, TNF inhibitors, glucocorticoids and NSAIDs increased the HR. Infliximab and glucocorticoids (equivalent prednisolone dose >15 mg/day) produced the highest HZ risk (HR: 2.91, 95% CI: 1.72, 4.89; HR: 2.85, 95% CI: 2.15, 3.77, respectively). Conclusion. Female sex, comorbidities and medications increased HZ risk in patients with rheumatic diseases and even young patients could develop HZ. Compared with RA, SLE and BS are stronger HZ risk factors. Patients with rheumatic diseases and these risk factors are potential target populations for HZ vaccination.