Phase B: In this phase of the study, health records of participants who have participated in the phase A of the study for the entire follow-up period and the 12 months period prior to the participants' enrolment will be retrieved from the BC Linked Health Database. In addition, the investigators will identify cases of asthma in the entire British Columbia population based on the administrative data for the same period of time. The BC Linked Health Database is a longitudinal administrative health care database containing participant-specific, anonymized health data from 1985 onwards on British Columbia's 4 million residents with health insurance. Records will be matched based on participants' unique Personal Health number and hence the matching will be almost completely accurate. Data extracted from the BC Linked Health Database will include Medical Services Plan data, which encompass fee-for-service physicians, the Discharge Abstracts Database of hospital inpatient separation records, as well as records of death certificates. Prescription drug use will be determined from the BC Pharmanet database. This is a population-based prescription drug database that captures essentially all dispensing episodes by outpatients residing in the province on a prescription-by-prescription basis (regardless of funding source)..