Twenty Years of Medically-Attended Pediatric Varicella and Herpes Zoster in Ontario, Canada: A Population-Based Study

<div><p>Objective</p><p>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.</p><p>Methods</p><p>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).</p><p>Results</p><p>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.</p><p>Conclusion</p><p>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.</p></div

Incidence of varicella a) physician office visits (n = 600,208), b) ED visits (n = 55,472), and c) hospitalizations (n = 2,701) among Ontario children by fiscal years 1992–2011.

<p>Incidence of varicella a) physician office visits (n = 600,208), b) ED visits (n = 55,472), and c) hospitalizations (n = 2,701) among Ontario children by fiscal years 1992–2011.</p

Median (IQR) age of varicella cases by clinical setting in the pre-varicella vaccine period, the privately-available varicella vaccine period and varicella vaccine program period.

<p>Notes: 1. SSTI (Skin and soft tissue infection). 2. ICU (Intensive care unit). 3. For varicella-associated SSTI, privately-available varicella vaccine period consists of FY 2002–2003.</p><p>Median (IQR) age of varicella cases by clinical setting in the pre-varicella vaccine period, the privately-available varicella vaccine period and varicella vaccine program period.</p

Age-specific varicella physician office visits among Ontario children by fiscal year, 1992–2011.

<p>Age-specific varicella physician office visits among Ontario children by fiscal year, 1992–2011.</p

Incidence of herpes zoster physician office visits, ED visits and hospitalizations among Ontario children 5–17 years by fiscal years 1992–2011.

<p>Incidence of herpes zoster physician office visits, ED visits and hospitalizations among Ontario children 5–17 years by fiscal years 1992–2011.</p

Comparison of incidence of medically-attended varicella and hospitalization for complicated varicella in Ontario children among pre-varicella vaccine, privately-available varicella vaccine and varicella vaccine program periods.

<p>Notes: 1. For varicella-associated SSTI, privately-available varicella vaccine period consists of FY 2002–2003.</p><p>Comparison of incidence of medically-attended varicella and hospitalization for complicated varicella in Ontario children among pre-varicella vaccine, privately-available varicella vaccine and varicella vaccine program periods.</p

Antimicrobial resistance of invasive non Hib strains isolated in Ontario, 2010–2014 (n = 664).

<p>*indicates resistance breakpoints have not been established</p><p>#indicates both resistance and intermediate category. Non-susceptible and intermediate (= NS)</p><p>Antimicrobial resistance of invasive non Hib strains isolated in Ontario, 2010–2014 (n = 664).</p

Incidence rate of invasive non-type b Hi by serotype in Ontario, 2004–2013 (n = 1,307).

<p>Incidence rate of invasive non-type b Hi by serotype in Ontario, 2004–2013 (n = 1,307).</p

Incidence rate of invasive non-type b Hi by serotype and age group in Ontario, 2004–2013 (n = 1,290).

<p>Incidence rate of invasive non-type b Hi by serotype and age group in Ontario, 2004–2013 (n = 1,290).</p

Data abstraction, cleaning and linkage for non-Hib cases 2004–2013, Ontario, Canada.

<p>Data abstraction, cleaning and linkage for non-Hib cases 2004–2013, Ontario, Canada.</p