The Rising Prevalence of Asthma: True Increase, Diagnostic Exchange or Diagnostic Accuracy?

Abstract

In the midst of frequent reports about "the asthma epidemic," results from a number of studies by the Manitoba Centre for Health Policy have shown stable or decreasing prevalence of an overall indicator of respiratory diseases which includes asthma. To resolve these apparently contrary findings, we conducted a time trend analysis using administrative data. Results revealed significant potential for diagnostic exchange: asthma prevalence increased, but that of bronchitis decreased. RésuméDans le contexte des fréquents rapports indiquant une « épidémie d' asthme », les résultats de plusieurs études effectuées par le Centre des politiques de santé du Manitoba montrent une prévalence stable ou en déclin d'un indicateur global des maladies respiratoires, y compris l' asthme. Afin de résoudre la contradiction apparente de ces résultats, nous avons effectué une analyse évolutive des tendances au moyen de données administratives. Les résultats révèlent une forte possibilité de substitution de diagnostic : la prévalence de l' asthme a augmenté, mais celle de la bronchite a diminué.

Post-tuberculosis airway disease: A population-based cohort study of people immigrating to British Columbia, Canada, 1985–2015

“…The primary outcome for our study, time-to-airway disease, was defined by total respiratory morbidity (TRM), which is an indicator variable developed by the Manitoba Centre for Health Policy for use with health administrative data in order to overcome coding variability between providers, patients of differing ages, and over time [22]. First published in 1993 [23], TRM has been used in various publications, spanning almost three decades, as a measure of airway disease incidence and prevalence in administrative data [22]. TRM was measured by the following diagnostic codes (ICD-9-CM: 466, 490À493, and 496; ICD-10-CA: J20-J21, J40-J45): asthma, bronchitis, bronchiolitis, emphysema, and chronic airway obstruction [22].…”

“…First published in 1993 [23], TRM has been used in various publications, spanning almost three decades, as a measure of airway disease incidence and prevalence in administrative data [22]. TRM was measured by the following diagnostic codes (ICD-9-CM: 466, 490À493, and 496; ICD-10-CA: J20-J21, J40-J45): asthma, bronchitis, bronchiolitis, emphysema, and chronic airway obstruction [22]. In our cohort, airway disease was ascertained from BC's hospital discharge abstracts, outpatient physician claims, and vital statistics death certificates.…”

Physical activity trails in an urban setting and cardiovascular disease morbidity and mortality in Winnipeg, Manitoba, Canada: a study protocol for a natural experiment

“…The most robust approach to test this research hypothesis is a quasiexperimental interrupted time series analysis with a comparison condition. The proposed interrupted time series analysis is strengthened by the use of a social and health data repository that provides an opportunity to link census, social and health data for the entire population of the City of Winnipeg beginning in 1995 22–27. Interrupted time series designs are considered the most valid quasiexperimental designs when a randomised controlled trial is not possible 28 29.…”

Policy‐induced selection bias in pharmacoepidemiology: The example of coverage for Alzheimer's medications in British Columbia

“…Multiple situations have been shown to influence the utilization of specific diagnostic codes, including a change in codes or the coding system, 5,6 the introduction of new diagnostic criteria, 7,8 increased awareness by physicians and the public for a specific disease, 9 and the substitution of codes for one disease with codes for another (diagnostic shift). [10][11][12][13][14][15][16][17] In the Canadian Province of British Columbia (BC), we identified a unique opportunity to examine the susceptibility of diagnostic coding behavior to a change in drug reimbursement policy. In October 2007, the provincial drug plan began covering the cholinesterase inhibitor medications (ChEIs: donepezil, galantamine, and rivastigmine) for patients with Alzheimer's disease (AD) as part of the Alzheimer's Drug Therapy Initiative (ADTI).…”

“…Inaccuracies in diagnostic coding have been discussed as an important source of bias; however, such inaccuracies were generally assumed to be constant over the study period, in spite of evidence that this might not be the case. Multiple situations have been shown to influence the utilization of specific diagnostic codes, including a change in codes or the coding system, the introduction of new diagnostic criteria, increased awareness by physicians and the public for a specific disease, and the substitution of codes for one disease with codes for another (diagnostic shift) …”