2.1 Identification of patients with CRSwNP
The data was available from 1 January 2000 to 31 December 2019. The study cohort included incident adult patients with a diagnosis of CRSwNP between 1 January 2012 to 31 December 2018. The patients were identified on their index date, the date of first CRSwNP diagnosis, by having any of the following ICD-10 diagnosis codes: J32.4 or J33.0, J33.1, J33.8, J33.9, or a polypectomy of internal nose reported by the Nordic Classification of Surgical Procedures (NCSP) code DHB20. Patients with cystic fibrosis (E84*) or ciliary dyskinesia (Q33*, Q34*) were excluded from the study.
The patients were identified from the national Finnish Care Register for Health Care (Hilmo) and Register of Primary Health Care (Avohilmo) visits, from where their diagnoses, procedures, visits, and resource utilization were extracted. The data from the Care Register for Health Care was complemented with data from the Social Insurance Institution (SII) for reimbursed medications and purchases, and with data from Statistics Finland for vitality status and causes of death.
Data from 2000-2012 was used to assess comorbidities and clinical characteristics. The baseline period was set to 36 months prior to index, where baseline comorbidities and characteristics were described. Patients were followed up until the end of the study (31 January 2019) or death. Data for at least one year of follow-up was available for all patients (Figure 1).