“…We identified the following comorbidities from the claims data by using ICD-9-CM codes: End-stage renal disease (ESRD; ICD-9-CM 585.6, 403.01, 403.11, 403.91, 404.02, 404.03, 404.12, 404.13, 404.92, 404.93, and V45.1), diabetes mellitus (DM; ICD-9-CM 250, 357.2, 362.0x, and 366.41), liver cirrhosis (LC; ICD-9-CM 571.2 and 571.5–571.6), autoimmune disease (ICD-9-CM 710.0, 710.1, 710.3, 710.4, 710.2, 714.30–714.33, 446.0, 446.2, 446.4, 446.5, 446.7, 443.1, 136.1, 694.4, 555, 556.0–556.6, and 556.8–556.9), and obesity (ICD-9-CM 278); tonsillectomy or adenotonsillectomy were also identified [ 26 , 27 , 28 , 29 ]. We included one of these comorbidities only if its corresponding code was present in at least three outpatient diagnoses or one inpatient diagnosis.…”