Seasonality and etiology of croup in pediatric patients hospitalized with lower respiratory tract infections: A long-term study between 2009 and 2017

Purpose: Croup is a common respiratory disease in children. The aim of this study was to analyze the epidemiology, etiology, and seasonal variations of respiratory virus infections in children with croup. Methods: From October 2009 to September 2017, children admitted with croup to Gachon University Gil Medical Center under the age of 18 years were enrolled in this study. We retrospectively reviewed patients' medical records. Results: A total of 1,053 of 27,330 patients (3.9%) infected with lower respiratory infections were diagnosed as having croup. In the age distribution, croup was most common (50.0%) in children aged 1 to < 2 years. There were 2 peaks, the major in summer (July to August) and the minor in spring (March to May). Parainfluenza virus type 1 (15.8%) was most prevalent and coincided with the summer peaks of croup. Influenza virus type B and parainfluenza virus type 3 were the most frequent etiologic agents in a spring peak of croup. Although parainfluenza virus type 1 was predominant of all ages, human coronavirus was a significant cause of croup in children younger than 1 year, whereas influenza virus played an important role in children above the age of 3 years. Conclusion: Seasonality and epidemiology of croup varied with age and regions.Two peaks of seasonal fluctuation were in summer and spring, which were related to the seasonality of respiratory viruses in croup. These results may be helpful in planning clinical and research needs.