Methodological Notes – Disease Incidence Module
Updated: January 2019
Concepts and Definitions
The occurrence of new cases of diseases, not all of which result in death, is another important dimension in the assessment of health in a population. CircHOB monitors the incidence of cancer and two infectious diseases – tuberculosis and gonorrhea.
Cancer
Cancer is one of the few chronic, non-communicable diseases for which population-based registries have been in existence for decades, at least among the developed countries. Cancer registration is complex and requires an adequate health care infrastructure to maintain and sustain it. Registries differ in their comprehensive coverage of cases and the quality of the data captured. CircHOB reports age-standardized incidence rates (ASIR) of cancer, both for all cancers combined, and several more common sites, including lung, colon and rectum (the last two tend to be combined in some countries) in both sexes, prostate in men, and breast and cervix in women. A “case” refers to the anatomical site on which a new primary case occurs, and not from secondary spread from some other site. Only malignant cases (ICD-10 codes C00-C96) are reported – benign and in-situ neoplasms are excluded.
For age-standardization, a hypothetical standard population known as the “world standard population” is widely used in international comparisons of cancer incidence rates, developed by the International Agency for Research on Cancer (IARC) http://www-dep.iarc.fr/WHOdb/glossary.htm. The age distribution in a population of 100000 people is as follows:
| Age group | Population |
|---|---|
| 0-4 | 12,000 |
| 5-9 | 10,000 |
| 10-14 | 9,000 |
| 15-19 | 9,000 |
| 20-24 | 8,000 |
| 25-29 | 8,000 |
| 30-34 | 6,000 |
| 35-39 | 6,000 |
| 40-44 | 6,000 |
| 45-49 | 6,000 |
| 50-54 | 5,000 |
| 55-59 | 4,000 |
| 60-64 | 4,000 |
| 65-69 | 3,000 |
| 70-74 | 2,000 |
| 75-79 | 1,000 |
| 80-84 | 500 |
| 85+ | 500 |
| Total | 100, 000 |
The “European standard population” is used by CircHOB to compare age-standardized mortality rates (ASMR) – see Methodological Notes: Mortality Module. The calculation for ASIR is the same as that for ASMR. The ASIRs can only be compared among themselves, or with any of the published rates in IARC or other scientific publications that use the same world standard population. They cannot be compared with published rates by some national agencies that use that country’s population from a specific year as the standard.
Infectious Diseases
Although the public health significance of infectious diseases has decreased substantially in recent decades, the overall burden of infectious diseases in the Arctic remains high, especially among the indigenous populations in some regions. Disease surveillance is an integral part of public health practice in the national and regional health care systems of circumpolar countries. Tuberculosis (TB) and gonorrhea are socially and epidemiologically important diseases which are reported consistently and regularly by all the regions. As both diseases are treatable and preventable, their incidence also reflects on the performance of the health system.
Infectious diseases are defined on the basis of their causative microorganisms, Mycobacterium tuberculosis for tuberculosis and Neisseria gonorrhœae for gonorrhea. There are operational case definitions used by public health agencies for the purpose of surveillance – see, for example, the ones used by the Centers for Disease Control and Prevention (CDC) of the United States https://wwwn.cdc.gov/nndss/conditions/.
Inclusion and exclusion criteria vary across different jurisdictions, and in the absence of laboratory confirmation, cases defined on the basis of clinical signs and symptoms and other investigations (such as X-ray) may not be completely comparable internationally. CircHOB accepts as confirmed cases those that are reported by the various public health agencies.
The annual incidence rate of a disease = (number of new cases reported in Year X) / (mean population of year X)This is usually expressed as the number of cases per 100, 000 persons. Crude rather than age-standardized rates are reported for TB and gonorrhea.
