Incidence of Hospitalizations and Emergency Department Visits for Herpes Zoster in Immunocompromised and Immunocompetent Adults in Ontario, Canada, 2002-2016

Background. Immunocompromised adults are at increased risk of herpes zoster (HZ) infection and related complications. We aimed to assess the incidence of hospital-attended HZ (ie, seen in hospital or emergency department) in immunocompromised populations and compare it to immunocompetent populations. Methods. We calculated incidence rates (IRs) of hospital-attended HZ in Ontario, Canada, between 1 April 2002 and 31 August 2016 in adults >= 18 years of age categorized as immunocompromised or immunocompetent. We repeated these analyses by type of immunocompromising condition and provided incidence rate ratios (IRRs) comparing to immunocompetent adults. We also calculated IRs and IRRs of HZ complications by immunocompromised status. Results. There were 135 206 incident cases of hospital-attended HZ during the study period. Immunocompromised adults accounted for 13% of these cases despite representing 3% of the population. The risk of hospital-attended HZ was higher for immunocompromised adults compared with immunocompetent adults (IRR, 2.9 [95% confidence interval {CI}, 2.9-3.0]) and ranged across type of immunocompromising conditions, from 2.6 (95% CI, 2.6-2.7) in those with a solid tumor malignancy to 12.3 (95% CI, 11.3-13.2) in those who had undergone hematopoietic stem cell transplant. The risk of any HZ complication was higher in immunocompromised adults (IRR, 3.6 [95% CI, 3.5-3.7]) and highest for disseminated zoster (IRR, 32.8 [95% CI, 27.8-38.6]). Conclusions. The risk of hospital-attended HZ and related complications was higher in immunocompromised populations compared with immunocompetent populations. Our findings underscore the high-risk nature of this population and the potential benefits that may be realized through HZ vaccination.