Risk factors for herpes zoster in a large cohort of unvaccinated older adults: a prospective cohort study

We analysed data from a prospective cohort of 255024 adults aged 545 years recruited from 2006-2009 to identify characteristics associated with a zoster diagnosis. Diagnoses were identified by linkage to pharmaceutical treatment and hospitalization records specific for zoster and hazard ratios were estimated. Over 940583 person-years, 7771 participants had a zoster diagnosis; 253 (3.3%) were hospitalized. After adjusting for age and other factors, characteristics associated with zoster diagnoses included: having a recent immunosuppressive condition [adjusted hazard ratio (aHR) 1.58, 95% confidence interval (CI) 1.32-1.88], female sex (aHR 1.36, 95% CI 1.30-1.43), recent cancer diagnosis (aHR 1.35, 95% CI 1.24-1.46), and severe physical limitation vs. none (aHR 1.33, 95% CI 1.23-1.43). The relative risk of hospitalization for zoster was higher for those with an immunosuppressive condition (aHR 3.78, 95% CI 2.18-6.55), those with cancer (aHR 1.78, 95% CI 1.24-2.56) or with severe physical limitations (aHR 2.50, 95% CI 1.56-4.01). The novel finding of an increased risk of zoster diagnoses and hospitalizations in those with physical limitations should prompt evaluation of the use of zoster vaccine in this population.