Comorbidities in an asthma population 8-29 years old: a study from the Norwegian Prescription Database

Purpose: To examine the occurrence of chronic diseases and antimicrobial treatment in an asthma population 8-29 years old, compared with the general population.

Methods: In this cross-sectional study, the asthma population was identified from the general population (retrieved from a census covering the entire Norwegian population) using filled prescriptions on asthma drugs as a proxy measure of current asthma. The outcome was excess occurrence of specific diseases (comorbidity) among people with asthma, compared with the age-specific general population. Diseases were defined by filled prescriptions with specific diagnostic codes (International Classification of Primary Care 2nd edition [ICPC-2] or International Classification of Diseases 10th revision [ICD-10]) during a 1-year period in the Norwegian Prescription Database. Nine chronic diseases were examined: attention deficit/hyperactivity disorder, epilepsy, migraine, mental illness, cardiovascular disease, diabetes, autoimmune disorders, gastro-oesophageal reflux disease (GORD), and allergy. Additionally, antibacterials recommended for respiratory tract infections and antivirals were examined (defined by Anatomical Therapeutic Chemical codes). Standardized morbidity ratios (SMR) for each disease were calculated.

Results: Fifty-nine percent of the population with asthma had at least one of nine chronic diseases examined, compared with 18% in the general population. Few individuals with asthma had more than one additional chronic disease (6% of male subjects and 8% of female subjects). SMRs were increased for all diseases except diabetes, implying higher than expected occurrence of the specific diseases in people with asthma. This pattern was observed in both age groups (8-19 and 20-29 years) and genders. Allergy and GORD had highest SMR (range 3.2-4.8), whereas the other diseases were in the range 1.2-2.5.

Conclusions: An excess occurrence of comorbidities was found in the population with asthma. A majority of people with asthma had one additional chronic disease, and few had more than one.