Canadian Chronic Disease Surveillance System:
Summary of methods

Background

The Canadian Chronic Disease Surveillance System (CCDSS) is a collaborative network of provincial and territorial surveillance systems supported by the Public Health Agency of Canada (PHAC).

In each province and territory, the health insurance registry database is linked to the physician billing and hospitalization databases using the health card number as a unique personal identifier. Where available and specified by the case definition, data from the prescription drug databases are also linked.

Case definitions are applied to these linked databases to identify individuals with chronic diseases/conditions, and aggregate data are sent to PHAC. The aggregate data are used by PHAC to estimate chronic disease/condition incidence, prevalence, all-cause mortality and use of health services.

The start year for reporting CCDSS data varies by disease/condition. The determination of the first reported year aims to allow enough time to capture all prevalent cases, given the parameters of the disease/condition specific case definition, and to ensure previously prevalent cases are excluded from incident cases.

Diseases and conditions

In the current edition of the CCDSS Data Tool, data up to 2019–2020 are reported for the following diseases/conditions:

Cardiovascular diseases

• acute myocardial infarction
• heart failure
• hypertension, excluding gestational hypertension
• ischemic heart disease
• stroke
• hospitalized stroke

Chronic respiratory diseases

• asthma
• chronic obstructive pulmonary disease

Diabetes

• diabetes mellitus (types combined), excluding gestational diabetes

Mental illness

• use of health services for mental illness and alcohol/drug induced disorders
• use of health services for mood and anxiety disorders
• schizophrenia (use of health services and cumulative prevalence)

Musculoskeletal disorders

• use of health services for arthritis
• gout and other crystal arthropathies
• juvenile idiopathic arthritis
• osteoarthritis
• rheumatoid arthritis
• osteoporosis
• osteoporosis-related fractures (any fracture, forearm, hip, humerus, pelvic, spine)
• osteoporosis-related fracture care gap (diagnosis, bone mineral density test, medication)

Neurological conditions

• dementia, including Alzheimer disease
• epilepsy
• multiple sclerosis
• parkinsonism, including Parkinson disease

Definitions of terms

Age-specific estimate/rate: Incidence, prevalence and all-cause mortality estimates/rates calculated for a five-year age group or a life-course age group (i.e., 1-19, 20-34, 35-49, 50-64, 65-79, 80+), using counts randomly rounded either up or down to a multiple of 5 (see random rounding). Data by five-year age groups are reported at the national level only.

Age-standardized estimate/rate: Incidence, prevalence and all-cause mortality estimates/rates age-standardized to the 2011 Canadian population in order to adjust for differences in population age structure, calculated using non-rounded counts and five-year age groups.

Case definition: CCDSS disease/condition specific case definitions are applied to identify individuals with the disease/condition (cases). Refer to the accompanying case definition documentation for the disease/condition specific criteria used, including the codes from the 9th or 10th edition of the International Classification of Disease (ICD), Canadian Classification of Health Interventions (CCI) and Canadian Classification of Diagnostic, Therapeutic and Surgical Procedures (CCP).

Coefficient of variation (CV): A measure used to describe the precision of an estimate/rate. More specifically, the CV of an estimate/rate is the ratio of the standard error of the estimate/rate to the estimate/rate itself. Estimates/rates with a CV between 16.6% and 33.3% should be interpreted with caution and those with a CV greater than 33.3% are not reported.

Confidence interval (CI): A statistical measurement of the reliability of an estimate/rate. The size of the CI relates to the precision of the estimate/rate, with narrow CIs indicating greater precision than those that are wide. The 95% CI shows an estimated range of values that is likely to include the true value 19 times out of 20.

Crude estimate/rate: Incidence, prevalence and all-cause-mortality estimates/rates calculated using counts randomly rounded either up or down to a multiple of 5 (see random rounding).

Fiscal year: CCDSS data are reported by fiscal year, April 1 to March 31.

Incidence rate: The number of new cases of a disease/condition occurring in a given time period in a population at risk, expressed as a rate.

Life-course age groups: The sequence of age categories individuals pass through as they age from childhood to older adult. The categories used for CCDSS reporting are: 1-19, 20-34, 35-49, 50-64, 65-79, 80+.

Mortality (all-cause) rate: The number of deaths from any cause occurring in a given time period, expressed as a rate.

Mortality (all-cause) rate ratio: The all-cause mortality rate among individuals with the disease/condition (cases) divided by the all-cause mortality rate among individuals without the disease/condition (non-cases). In CCDSS data reporting, these rates are age-standardized to account for the different age distribution between cases and non-cases. A rate ratio greater than one indicates that cases experience a higher mortality burden compared to non-cases, regardless of the cause of death. Assuming the baseline age-standardized mortality rates between cases and non-cases are similar, the difference in all-cause mortality can be attributed directly or indirectly to the disease/condition.

Prevalence estimate: The number of cases of a disease/condition present in a given time period in a population, expressed as a proportion. In the CCDSS Data Tool, prevalence may be reported over three different periods: annual (cases identified during one year), cumulative (cases identified during the capture period) and active (a subset of cumulative prevalence cases that meet the active prevalence criteria).

Data procedures

Before estimates/rates are calculated, the following data procedures are applied.

Age group aggregation for age-specific estimates/rates

Data submitted by provinces and territories by five-year age groups are aggregated using the following life-course age groups: 1-19, 20-34, 35-49, 50-64, 65-79 and 80+ with a few exceptions:

• For parkinsonism including Parkinson disease, osteoporosis, osteoporosis-related fractures and heart failure, the first age group is 40-49;
• For schizophrenia, the first age group is 10-19;
• For rheumatoid arthritis, the first age group is 16-34; and
• For juvenile idiopathic arthritis, only one age group is used, i.e. 0-15.

Suppression

Estimates, rates and rate ratios are not reported when the corresponding non-rounded counts are less than 10 or the coefficients of variation are greater than 33.3%.

Random rounding

To protect data confidentiality and avoid residual disclosure, crude estimates/rates are calculated using randomly rounded counts. All provincial/territorial and Canadian counts 10 or greater are randomly rounded either up or down to a multiple of 5. Random rounding is only used to calculate crude estimates/rates. Age-standardized estimates/rates are based on non-rounded counts.

Formulae used for calculation of prevalence, incidence and all-cause mortality

Prevalence estimate

$$\begin{gathered} {\displaystyle \mathrm{Annual} \\ \mathrm{prevalence}& =\frac{{\mathrm{Total\; number\; of\; individuals\; meeting\; annual} \\ \mathrm{case\; definition\; during\; the\; fiscal\; year}& }_{}^{}}{{\mathrm{Total\; number\; of\; individuals\; with\; valid} \\ \mathrm{health\; insurance\; during\; the\; fiscal\; year}& }_{}^{}}\times \mathrm{100\; or\; 100,000\; for\; osteoporosis-related} \\ \mathrm{fractures\; and\; hospitalized\; stroke\; events}} \end{gathered}$$

$$\begin{gathered} {\displaystyle \mathrm{Cumulative} \\ \mathrm{prevalence}& =\frac{{\mathrm{Total\; number\; of\; individuals\; who\; met\; the\; case\; definition\; during} \\ \mathrm{the\; capture\; period\; and\; who\; are\; alive\; during\; the\; fiscal\; year}& }_{}^{}}{{\mathrm{Total\; number\; of\; individuals\; with\; valid} \\ \mathrm{health\; insurance\; during\; the\; fiscal\; year}& }_{}^{}}\times \mathrm{100}} \end{gathered}$$

$$\begin{gathered} {\displaystyle \mathrm{Active} \\ \mathrm{prevalence}& =\frac{{\mathrm{Total\; number\; of\; cumulative\; prevalence} \\ \mathrm{cases\; meeting\; active\; case\; definition}& }_{}^{}}{{\mathrm{Total\; number\; of\; individuals\; with\; valid} \\ \mathrm{health\; insurance\; during\; the\; fiscal\; year}& }_{}^{}}\times \mathrm{100}} \end{gathered}$$

Incidence rate

$$\begin{gathered} {\displaystyle \mathrm{Incidence\; rate}& =\frac{{\mathrm{Total\; number\; of\; incident\; cases\; during\; the\; fiscal\; year}& }_{}^{}}{{\mathrm{Total\; number\; of\; individuals\; with\; valid\; health\; insurance} \\ \mathrm{during\; the\; fiscal\; year\; –\; prevalent\; cases\; +\; incident\; cases}& }_{}^{}}\times \mathrm{100,000}} \end{gathered}$$

Mortality (all-cause) rates and rate ratio

$$\begin{gathered} {\displaystyle \mathrm{Mortality\; (all-cause)\; rate} \\ \mathrm{with}\mathrm{ the\; disease/condition}& =\frac{{\mathrm{Total\; number\; of\; deaths\; from\; all\; causes\; during\; the\; fiscal} \\ \mathrm{year\; among\; individuals }\mathrm{with}\mathrm{ the\; disease/condition}& }_{}^{}}{{\mathrm{Total\; number\; of\; individuals }\mathrm{with}\mathrm{ the} \\ \mathrm{disease/condition\; during\; the\; fiscal\; year}& }_{}^{}}\times \mathrm{100,000\; or\; 1,000} \\ \mathrm{for\; hip\; fracture}} \end{gathered}$$

$$\begin{gathered} {\displaystyle \mathrm{Mortality\; (all-cause)\; rate} \\ \mathrm{without}\mathrm{ the\; disease/condition}& =\frac{{\mathrm{Total\; number\; of\; deaths\; from\; all\; causes\; during\; the\; fiscal} \\ \mathrm{year\; among\; individuals }\mathrm{without}\mathrm{ the\; disease/condition}& }_{}^{}}{{\mathrm{Total\; number\; of\; individuals }\mathrm{without}\mathrm{ the} \\ \mathrm{disease/condition\; during\; the\; fiscal\; year}& }_{}^{}}\times \mathrm{100,000\; or\; 1,000} \\ \mathrm{for\; hip\; fracture}} \end{gathered}$$

$$\begin{gathered} {\displaystyle \mathrm{Rate\; ratio\; of\; (age-standardized)} \\ \mathrm{mortality\; (all-cause)\; rates}& =\frac{{\mathrm{All-cause\; mortality\; rate\; among} \\ \mathrm{individuals }\mathrm{with}\mathrm{ the\; disease/condition}& }_{}^{}}{{\mathrm{All-cause\; mortality\; rate\; among} \\ \mathrm{individuals }\mathrm{without}\mathrm{ the\; disease/condition}& }_{}^{}}} \end{gathered}$$

Provincial and territorial notes

• Newfoundland and Labrador: Data before 2008–2009 are excluded.
• Northwest Territories: Data were not available.
• Nunavut: Data before 2005–2006 are excluded. Data were not available for 2019–2020.
• Quebec: Data were not available for 1995–1996. Data cells with counts smaller than 5 were suppressed by Quebec and substituted with random numbers (1-4) by PHAC. As a result, age-specific incidence and mortality rates may be randomly over or under estimated.
  The modernization of the billing system for fee-for-service medical services by the Régie de l'assurance maladie du Québec (RAMQ) in 2016 has resulted in a decrease in the entry of diagnostic codes in the fee-for-service medical services file. Data for 2016–2017 and subsequent years should therefore be interpreted with caution, as a slight underestimation is suspected.
• Saskatchewan: Data cells with counts smaller than 5 were suppressed by Saskatchewan and substituted with random numbers (1-4) by PHAC. As a result, age-specific incidence and mortality rates may be randomly over or under estimated.
• Yukon: Data before 2010–2011 are excluded.

Note: All disease/condition-specific notes, including provincial/territorial specifications, are included in the CCDSS case definitions documentation.