title: Twenty Years of Medically-Attended Pediatric Varicella and Herpes Zoster in Ontario, Canada: A Population-Based Study.
abstract: OBJECTIVE
  To determine if reductions in medically-attended pediatric varicella and herpes zoster occurred in Ontario, Canada, after publicly-funded varicella immunization was implemented in 2004.
  
  
  METHODS
  For fiscal years (FY) 1992-2011, we examined data on varicella and herpes zoster physician office visits, emergency department (ED) visits, hospitalizations (including for varicella-associated skin and soft tissue infections [SSTI]), and intensive care unit (ICU) admissions, among those aged <18 years. The pre-vaccine, privately-available, and vaccine program eras were FY1992-1998, FY1999-2003, and FY2004-2011, respectively. We used Poisson regressionand Kruskal-Wallis tests (all at the p<0.05 level of significance), and compared rates using incidence rate ratios (IRRs) and 95% confidence intervals (CIs).
  
  
  RESULTS
  Incidence of varicella office visits declined over the study period from a high of 25.1/1,000 in FY1994 to a low of 3.2/1,000 in FY2011. ED visits and hospitalizations followed similar patterns of decreasing rates later in the study period. IRRs comparing the vaccine program versus pre-vaccine eras were 0.29 (95%CI: 0.26-0.32) for office visits, 0.29 (95%CI: 0.21-0.40) for ED visits, and 0.41 (95%CI: 0.10-1.69) for hospitalizations. Annual declines in varicella office visits were 7.7%, 9.1%, 8.4%, and 8.4% per year among children aged <1 year, 1-4 years, 5-11 years, and ≥12 years, respectively (all p<0.001). Age-specific rates of varicella-associated SSTI declined significantly among children <12 years (p<0.001) and rates of ICU admissions decreased significantly for children <1 year (p = 0.02). (p<0.001) over the study period. For children aged 5-17 years, herpes zoster office visits decreased whereas ED visits increased (both p<0.001) and there was a small, non-significant (p = 0.07), decrease in hospitalizations.
  
  
  CONCLUSIONS
  Medically-attended varicella decreased during the study period, particularly since varicella vaccine was publicly-funded. Results suggest immunization program-related changes in varicella epidemiology, including herd effects, demonstrated by reductions in varicella in program-ineligible age groups. We did not observe a consistent impact on herpes zoster.
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada; Division of Paediatric Medicine, Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Anne E
authors.initials: AE
authors.lastname: Wormsbecker
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada.
authors.forename: Jun
authors.initials: J
authors.lastname: Wang
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada; Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada; Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada.
authors.forename: Laura C
authors.initials: LC
authors.lastname: Rosella
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada; Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada; Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada.
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Kwong
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada.
authors.forename: Chi Yon
authors.initials: CY
authors.lastname: Seo
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada; Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Natasha S
authors.initials: NS
authors.lastname: Crowcroft
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada; Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Shelley L
authors.initials: SL
authors.lastname: Deeks
mesh_terms: D000293:Adolescent; D002644:Chickenpox / Q000453:epidemiology* / Q000517:prevention & control*; D002648:Child; D002675:Child, Preschool; D003695:Delivery of Health Care / Q000191:economics / Q000706:statistics & numerical data*; D005260:Female; D005380:Financing, Government; D006562:Herpes Zoster / Q000453:epidemiology* / Q000517:prevention & control*; D006801:Humans; D007114:Immunization; D007223:Infant; D008297:Male; D009864:Ontario / Q000453:epidemiology