2.2. Definitions
Adult asthma was defined based on the following criteria: (1) 18 years
of age or older, (2) at least two claims under the 10th revision of the
International Statistical Classification of Diseases and Related Health
Problems (ICD-10) codes J45–46, and (3) at least one claim for
prescription of asthma-related drugs including inhaled or systemic
corticosteroids, bronchodilators, leukotriene receptor antagonists, or
xanthine derivatives12,13. The index event for
incident asthma was defined as the first prescription of asthma-related
medication with ICD codes J45–46 as a major or minor diagnosis between
January 1, 2005, and December 31, 2006, with no diagnosis code more than
three years before the first index event after the sensitivity test. The
baseline period was defined as 12 months before the index date. The
follow-up period was from the index date to the date of death or
December 31, 2015.