Population of this study
This study passed the scrutiny of the Institutional Review Board of Jeonbuk National University Hospital (IRB number 2020-08-012). This time series analysis was conducted using the anonymized Korea National Health Insurance Service-National Sample Cohort (KNHIS-NSC) database, and data in the period from January 1, 2007 to December 31, 2012 were analyzed. This database includes day of hospital visit, the patient’s age, sex, residential area, economic level, diagnosis, medical history, and disease code. The diagnostic codes from KNHIS-NSC are based on the International Classification of Diseases, Tenth Revision (ICD-10). In 2007, the population in Korea was 49,194,085, of which 1 million cohorts of randomly stratified samples were used by the KNHIS-NSC databases.
The inclusion criteria of the CE population from this database were: 1) patients assigned code J441 in the ICD-10 classification at the time of the hospital visit; 2) patients taking oral steroids; and 3) patients with chest computed tomography scans.5,6 Individuals were divided into four age groups: preschool age (0 to 4 years old), school age (5 to 19 years old), adult (20 to 59 years old), and elderly (≥60 years old).