These asthma statistics use four Ontario health care administrative databases housed at the Institute for Clinical Evaluative Sciences (ICES):

The Ontario Health Insurance Plan (OHIP) database includes information pertaining to services provided by Ontario physicians who are paid on a fee-for-service basis. These records were used to capture out-of-hospital physician services and laboratory tests, as well as in-hospital services and diagnostic test interpretation performed by fee-for-service physicians. The fee code associated with each billable patient encounter was used to identify visits for asthma.

The Canadian Institute for Health Information Discharge Abstract Database (CIHI-DAD) is a national database comprised of information on inpatient hospitalizations, which includes data for same day surgeries, long-term care and rehabilitation. Each abstract in the database is associated with a patient discharge. Beginning in 2002-03, health care facilities used the International Classification of Diseases, Ninth Revision (ICD-9) and Tenth Revision (ICD-10) for DAD submissions to CIHI. Prior to 2002-03, 16 ICD-9 diagnostic codes were used to identify hospitalizations due to asthma.

The National Ambulatory Care Reporting System (NACRS) database contains data for hospital-based and community-based emergency and ambulatory care (for example, day surgery and outpatient clinics).

The Registered People Database (RPDB) of the Ontario Ministry of Health and Long-Term Care provides information about individuals who are registered for OHIP. The database collects and maintains information regarding health card number, surname, date of birth, gender, address, and date of death, if applicable.

The ICES Physician Database (IPDB), which comprises information from the Corporate Provider Database (CPDB), the Ontario Physician Human Resource Data Centre (OPHRDC) database and the OHIP database of physician billings, was used to define health care utilization by physician specialty. The CPDB contains information about physician demographics, specialty training and certification and practice location. This information is validated against the OPHRDC database, which is updated through periodic telephone interviews with all physicians practicing in Ontario.

The index date for the study cohort was defined as the first asthma diagnosis after April 1, 1991. Individuals who were aged 0 to 99 years, were residents of Ontario at the index date and contained no missing gender information in the Registered People Database (RPDB) database were included in the cohort.

For the purposes of this study, all OHIP claims that occurred after the index date were extracted, including medical and non-medical physician billings, as well as laboratory and non-laboratory billings. The ICD-9 free code 493 was used to identify the subset of asthma OHIP claims made from July 1, 1991 onward. Since it is possible for multiple OHIP billings to occur for each patient, only one claim per physician, per service day, per patient was used to represent a health care visit.

All inpatient acute care hospital admissions and same day surgeries occurring after the index date were extracted from the CIHI database. ICD-9 code 493 and ICD-10 code J45 were used to identify the subset of asthma hospitalizations.

Asthma population

An individual was considered to have asthma if he/she had one asthma hospitalization record in the CIHI database, or two asthma OHIP claims over the course of two consecutive years from 1991-92 onward. The diagnosis date was taken as the earlier of either the first asthma hospitalization or the first of two OHIP claims that comprised the asthma algorithm.1,2

Although data were available as of 1991-92, only data from 1996-97 and onward are exhibited. Five years of prior data (1991-92 through 1995-96) were used to confirm asthma incidence, in order to accurately capture individuals with asthma. Therefore, data from fiscal years 1991-92 to 1995-96 were excluded from these statistics.

Prevalent cases include people from the asthma cohort who had at least one OHIP claim or hospitalization for asthma within any given fiscal year from 1996-97 onward.

The incidence date of asthma was defined as the first diagnosis date – that is, the first hospitalization or OHIP claim with a diagnosis of asthma according to the algorithm.

To address trends in health care utilization in individuals with asthma as measured by the rate of OHIP claims per individual, all office visits to Ontario medical physicians were extracted from the OHIP database. The rates of hospitalizations and ED visits per 100 population in individuals with asthma were calculated. The denominators used to calculate the rates were the number of individuals with asthma in Ontario.

1To T, Cicutto L, Dell S, Dick PT, MacLusky I. Case verification of children with asthma in Ontario. Pediatric Allergy and Immunology 2006; 17:69-76.
2Gershon AS, Wang C, Guan J, Vasilevska-Ristovska J, Cicutto L, To T. Identifying patients with physician diagnosed asthma in health administrative databases. Can Respir J. 2009 Nov-Dec;16(6):183-8.

Copyright © 2012 Ontario Asthma Surveillance Information System (OASIS). All rights reserved. No parts of our reported tables, graphs or maps may be reproduced or submitted to any media including journal, magazines, newspapers, radio or TV without the proper written permission of OASIS and ICES.

Users of our statistics will include the following disclaimer and acknowledgement in citations of parts or all of the asthma statistics provided by OASIS:

This presentation (as appropriate) uses asthma statistics reported by the Ontario Asthma Surveillance Information System (OASIS) and data provided by the Institute for Clinical Evaluative Sciences (ICES), Ontario”