Objective — Croup is the most common form of airway obstruction in children. Known to be primarily viral, the seasonality of croup has been examined largely through its association with the human parainfluenza viruses. This study examined the seasonal pattern of croup hospitalizations in relation to age and gender for the province of Ontario during a 14-year period.
Methods — A retrospective, population-based study design was used to examine seasonal and temporal patterns of croup hospitalizations from April 1, 1988, to March 31, 2002. All residents of Ontario who were aged 0 to 4 years and eligible for universal health coverage during the study period were included for analysis. Time-series analyses then were conducted on monthly aggregations of hospitalizations.
Results — This study found strong evidence of croup hospitalization seasonality, with a biennial midautumn peak and annual summer trough, evident throughout the 14-year study period (Fisher's κ = 51.11; Bartlett Kolmogorov Smirnov = 0.552). The pattern was observed in all children aged 0 to 4, although boys were hospitalized 2 times more often than girls of the same age. Rates of croup hospitalization were lower for children aged 1 to 4 years than for children aged 0 to <1. A marked decrease in croup hospitalizations was observed after the winter of 1993/1994 and continued to decrease in a step-wise manner for the remainder of the study period.
Conclusions — This study delineates a clear biennial pattern of seasonal croup hospitalizations, varying by age and gender, with a large decrease in hospitalizations after the winter of 1993/1994. It is expected that these findings will have important implications for the treatment and management of childhood croup.