2.3. Study population
As shown in Supplemental Figure 1 , 738,254 patients 18 years of
age or older were identified from January 1, 2005 to December 31, 2006.
After excluding 16,995 subjects with malignancy during the washout
period, 697,281 patients were selected. Among these, 80,356 patients had
at least one claim for ICD-10 codes for asthma (J56–46).
Among the 80,356 patients with asthma, we excluded patients who had
asthma during the three-year washout period (n = 15,069), patients who
had only one claim under ICD-10 codes for asthma (n = 28,333), patients
who did not receive asthma-related medication (n = 16,592), and patients
who died during the baseline period (n = 55). Finally, a total of 19,319
patients with incident asthma was identified (asthma cohort). Next, we
performed 1:4 age and sex matching for each asthma patient from cohort
without asthma (control cohort). Patients were followed-up until the
date of death or December 31, 2015.
This study was approved by the Ethics and Review Board of Hanyang
University Guri Hospital (IRB No. 2019-11-018). The requirement of
informed consent from the participants was waived because the NHIS
database was constructed after anonymization.