Non-communicable diseases (NCDs) or chronic diseases account for a large proportion of increasing healthcare costs. Monitoring patterns and trends of chronic diseases provide critical information for public health actions (prevention, protection, and promotion) and healthcare planning. Since the 1990s, the BCCDR have been released each year to measure chronic disease burdens in BC, measure health inequalities, and support clinical and public health research.
The BCCDR utilises health care administrative data to determine the incidence and prevalence of chronic conditions in the province. The list below summarizes the main data sources and their purpose.
- Client Roster: A record of people who are registered in the BC healthcare system.
- Medical Services Plan (MSP): Information on all medically required services, including general practitioners and specialist visits, laboratory services, and diagnostic procedures.
- PharmaNet (PNET): Records for prescription drugs and benefit non-prescription drugs/medical supplies/devices dispensed to patients at community pharmacies in BC.
- Discharge Abstract Database (DAD): Abstract summaries of patient hospital stays.
Chronic disease case definitions are determined using health care system usage data. This data is obtained from administrative health service data holdings. The Client Roster data holding is used to obtain a record of people who use the BC health care system; it contains information on people who live or have lived in BC over time, specifically focusing on people who have registered in the health care system with a PHN. Health care system data is obtained for each person, including data on MSP, prescription drugs, and hospitalizations. This information is then used to assign chronic disease cases based on their definitions, and to calculate disease incidence and prevalence in the province. For osteoarthritis, for example, patients are ascertained as a case if they have 1 or more hospitalizations with osteoarthritis diagnosis codes, or 2 or more practitioner claims within 1 year with osteoarthritis diagnosis codes.
The trends and distributions of incidence and prevalence of chronic conditions are then studied according to BC health boundaries, age groups, and sex.
The following conditions are included in the BCCDR (25 chronic conditions, as well as 11 relapsing-remitting diseases indicated by a star):
- Chronic respiratory diseases: Asthma*, chronic obstructive pulmonary disease
- Cardiovascular diseases: Acute myocardial infarction*, heart failure, ischemic heart disease, stroke*, haemorrhagic stroke*, ischemic stroke*, transient ischemic attack*
- Neurological disorders: Alzheimer's and other dementias, epilepsy, multiple sclerosis, Parkinson’s disease
- Mental and substance use disorders: Depressive disorders*, anxiety and mood disorders*, schizophrenia & delusional disorders*, substance use disorders*
- Musculoskeletal disorders: Gout*, osteoarthritis, osteoporosis, rheumatoid arthritis, juvenile idiopathic arthritis
- Diabetes and kidney diseases: Diabetes mellitus, chronic kidney disease, hypertensive diseases, high blood pressure (hypertension)
A person is identified as having one of the chronic conditions in this report if they meet the criteria set out in the case definition for that specific condition. While the definitions are different for each condition, a typical case might be identified if the person has had a hospitalization diagnosis, a physician diagnosis, or drug utilization (i.e. from a pharmacy) - either alone or in combination - with a specified time frame relative to the year in question. For example, if a person has a hospitalization or two physician visits in any one year for asthma, or 2 asthma prescriptions in any single year, then they are counted as a case in every subsequent year.
Case definition criteria may be revised over time in response to new validation studies, new data sources, or new chronic disease surveillance or chronic disease management requirements. Where possible, case definitions used for national surveillance through the Canadian Chronic Disease Surveillance System (CCDSS) are adopted.
This measures the number and rate of people who have been newly diagnosed with the condition during a specific year - for example, all the people who never had asthma previously, but who were diagnosed with asthma during 2014/15. The incidence rate is the the number of incident cases divided by the population-at-risk during a specific year. Notably, the population-at-risk excludes the people who have been previously diagnosed with asthma.
This represents the proportion of people that are living with the condition in a specific year. For example, the number of prevalent cases for asthma in 2014/15 represents all the people that developed asthma in 2014/15 (incidence) along with all the people living with asthma that was diagnosed in a previous year. Prevalence is the number of prevalent cases divided by the total population in that year.
Conditions are considered episodic if they meet the case definition for a given year, and have further condition-related health service utilization in subsequent years. For example, if someone were to meet the case definition for depression in the previous fiscal year, and had an additional physician visit the following year for a depression-related service, they would meet the definition for episodic depression.
This refers to all the people in a given geography in a given year that have had contact with the BC Health Care system and had health insurance coverage in BC, or had other coverages or services paid for by the BC government. This includes the Medical Services Plan (MSP), drug dispensations paid by PharmaCare, and hospital discharge records.
This is a subset of the population, and reflects those at risk of developing a condition.
These rates are not adjusted to the standard population, and represent the number of cases in a specific geographic region divided by the population/population-at-risk in that region. Crude rates are representative of the burden of disease in the population.
To account for differences in the age structure of different geographical regions, rates are calculated as if all regions shared the same age structure, that of the 2011 Canadian Census. Age-standardized rates are appropriate for comparing regions or trends over time. They are not a good representation of the burden of disease in the population.
Confidence Intervals (CI):
The rates and proportion of disease in this report should be thought of as estimates, and therefore may not represent the true rate in a given place and time. Confidence intervals are the upper and lower limits within which the true value probably lies. For example, if the asthma incidence for BC in 2014/15 is 5.94, with CI's of 5.87 and 6.02, you can be very confident in that stated incidence. However, wide confidence intervals may suggest that there is uncertainty in the estimate. In this report, 95% CI's are used, which means that the true value should lie between the CI's 95% of the time.
Morbidity case definitions
While many case definitions have been validated in other Canadian jurisdictions or internationally, no case definitions have been validated in BC due to the lack of access to gold standard patient data. We expect the case definitions, especially definitions validated in other Canadian jurisdictions, to perform reasonably well in BC because of the similarities in overall healthcare systems. In some cases, we modified the case definitions after consulting with clinicians (physicians, nurses, and pharmacists), due to the differences in public health insurance coverage, disease coding, physician billing, and information management.
Case algorithms based on administrative data are never 100% sensitive (sensitivity is the ability to completely identify all cases of a given disease – true positives) or 100% specific (specificity is the ability to correctly identify non-cases – true negatives). Only persons using the BC healthcare system (primary care, hospital care, and/ or Pharmacare) can be identified as a chronic disease case. If a person does not use these services, there will be no diagnostic or treatment information available to qualify that person as a case. Also, individuals that were diagnosed in another province or another country and never used healthcare in BC for the conditions will not be identified as cases. Therefore, undiagnosed or untreated cases of disease will not be included in chronic disease estimates. As such, the chronic disease counts and rates/proportions may underestimate the actual number of cases in the province.
Prevalent cases misclassified as incident cases
Incident cases identified in the BCCDR might have been diagnosed with a chronic disease before the MoH data holdings started operating in 1992/93. In other words, many incident cases identified by BCCDR algorithms in early years were actually prevalent cases. This is reflected by the high incidence values for many diseases in the first few years of BCCDR and a trend of significant incidence decline over time during this period (i.e., reporting washout period). Therefore, the recommended reporting period for incidence and prevalence is from 2001/02 onwards.
Data source update
Administrative data sources at MoH are updated periodically, resulting in small changes of individual records. Every effort has been made to minimize the impacts of these updates on the BCCDR (e.g., creating snapshots of data sources), but discrepancies cannot be ruled out. The lack of complete synchronization among data sources might create discrepancies in some variables such as date of birth, place of residence, and service date. There is also a small proportion of records with unknown sex, date of birth, or health boundary assignment in the source tables. No imputations are conducted for these missing values when the BCCDR is created. Cases with
unknown sex or health boundary assignment values are included in the total number of cases at the provincial level, but, reporting on measures for unknown stratifiers such as health boundary specifically may not be meaningful and is likely misleading.
Health boundary changes
CHSAs are generated using DB boundaries for the Canada Census in 2016 (i.e., a DB-CHSA relationship table). Due to DB boundary changes over time, applying these boundaries to residential addresses in previous and later years might have resulted in CHSA misassignments (i.e., LHA/HSDA/HA misassignments) for these time periods.
There are two reasons for data being blank or marked with "<5" in a chart or table. The first is if the number of cases in a specific time and place are less than 5, then the value has been hidden. Second, if it is possible to back-calculate the number of cases using aggregated geographies or sex breakdowns, then other areas or sex breakdowns may also be suppressed. True zeros (0) remain in the data set.
The Ministry of Health and all Health Authorities in BC report for the year starting April 1 and ending March 31. For example, the 2014/15 fiscal year includes all cases identified between April 1, 2014 to March 31, 2015.