Introduction

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The purpose of this document is to provide updated case definitions for communicable diseases under national surveillance, diseases that federal, provincial and territorial public health officials have agreed to make nationally notifiable. Note that disease reporting to provincial/territorial public health officials is mandatory for selected diseases according to respective provincial/territorial legislation and that notification to the federal level is voluntary and by mutual agreement. The list of nationally notifiable diseases was revised and was published in 2006 ^(1,2); note that, since then, it was agreed to make invasive Haemophilus influenzae disease, type non-b, notifiable in addition to invasive Haemophilus influenzae disease, type b.

The process for updating the case definitions was extensive and included laboratory, clinical and epidemiologic aspects; it involved federal and provincial representatives as well as subject matter experts. For the epidemiologic and clinical aspects of the case definitions, input was provided by a federal/provincial/territorial consultative process undertaken and coordinated by the Public Health Agency of Canada (PHAC) (the Centre for Communicable Diseases and Infection Control, the Centre for Food-borne, Environmental and Zoonotic Infectious Diseases, and the Centre for Immunization and Respiratory Infectious Diseases) with approval by the Communicable Disease Control Expert Group of the Pan-Canadian Public Health Network.

For the laboratory aspects, input and approval was provided by the Laboratory Standardization Subcommittee of the Canadian Public Health Laboratory Network (CPHLN), which is an expert group of the Pan-Canadian Public Health Network involving collaboration between the National Microbiology Laboratory of PHAC and the provincial public health laboratories. Laboratory criteria for disease confirmation are based on current national and international guidelines, literature review and diagnostic laboratory technology and practices. These generally include a variety of markers based on the range of current diagnostic laboratory technology, availability of commercial and in-house test kits, and current laboratory practices and expertise across the country. All tests that are used to detect and confirm communicable diseases in accordance with case definitions should undergo a standard validation process before being introduced to ensure that they are accurate and reproducible. Further information on laboratory testing issues, including supplemental laboratory evidence for confirming nationally notifiable diseases, may be obtained from the National Microbiology Laboratory or the CPHLN.

Goals of disease notification for national surveillance purposes

1. To facilitate the control of the diseases under surveillance by identifying the following:
   1. prevailing incidence levels and trends to assist in the development of feasible objectives for prevention and control of the disease and the evaluation of control programs;
   2. epidemiologic patterns and risk factors associated with the disease to assist in the development of intervention strategies;
   3. outbreaks, for the purpose of timely investigation and control.
2. To satisfy the needs of government (including regulatory programs), health care professionals, voluntary agencies and the public for information on risk patterns and trends in the occurrence of communicable diseases.

Program characteristics

If a decision is made to put a disease under surveillance, then the surveillance or notification program should meet the following criteria:

1. use of a uniform case definition across Canada;
2. collection of sufficient, appropriate epidemiologic data on each case to fulfil program goals;
3. timely transmission of these data from local to provincial and federal agencies for analysis (personal identifying information should be removed before the data reach the federal level);
4. use of the data to enhance control programs and assist in the development of realistic objectives for reducing the number of preventable cases;
5. periodic evaluation of the effectiveness and economic benefit of the surveillance system and progress towards control of the disease.

It is acknowledged that full implementation of these steps will proceed at different rates in different jurisdictions.

Notification of diseases under national surveillance

Before 1990, each jurisdiction had its own set of communicable disease case definitions, and comparability across jurisdictions was difficult, if not impossible. In March 1991, the federal government, in conjunction with the provincial and territorial epidemiologists, published disease-specific case definitions for communicable diseases under national surveillance. For the first time, these case definitions provided standardized criteria for the notification of cases under national surveillance. A second edition of revised case definitions was published in 2000⁽³⁾. This current document represents a third edition; however, in the future it will be updated on a case-by-case, as needed basis rather than en bloc, and so future revisions will be posted on the PHAC website at: http://www.phac-aspc.gc.ca/publicat/ccdr-rmtc/index-eng.php

In most instances, only confirmed cases are notified to the federal Notifi able Disease Surveillance System of the Centre for Communicable Diseases and Infection Control, PHAC. Situations in which probable, possible or suspect cases are to be notified are noted within the case definitions for the relevant diseases. A combination of clinical, laboratory and epidemiologic criteria is used to classify a confirmed case. Some case definitions include a brief clinical description; however, this information is intended for the purpose of classifying cases and should not be used for clinical diagnoses. Probable, possible and suspect cases may be described to assist local public health authorities in carrying out their public health mandate, such as outbreak investigation and contact tracing. Physicians diagnosing a case of a specifi c (notifiable) disease report their clinical diagnosis with/without laboratory confirmation to local health authorities, and these authorities are responsible for determining whether the case meets the surveillance case definition before they proceed with official notification. When there is uncertainty because data are missing or the results are inconclusive, the case may be reported in the appropriate category (probable, possible, suspect), but if the status is changed later as a result of additional information, this change must be made in the notification system to avoid duplicate counting of cases.

The "core set" of variables

Federal, provincial and territorial officials have previously agreed on the essential or core epidemiologic data to be submitted for each notified case: province, disease, age, sex, status of case (confirmed, probable, possible or suspect), episode dates, episode identifier and geographic indicator. For some diseases, there has been further agreement to provide an additional set of variables ("minimum data set").

Notification of case-by-case data

It has been previously agreed that notifications should be made on a case-by-case or "linelisted" basis in which each case is notified on an individual basis with the core set of variables. However, some provinces/territories are still making the transition from supplying aggregate data to case-by-case data. All case notification to the federal level is non-nominal.

Protocols for interprovincial/territorial notification of disease

• The jurisdiction where the disease is diagnosed normally notifies the federal level or has the responsibility to make sure that the disease is notified by some jurisdiction.
• The jurisdiction of diagnosis informs the jurisdiction of residence if public health action (e.g. contact management, source of identifications) is necessary in the jurisdiction of residence.
• When cases resident in one jurisdiction are being diagnosed in another (such as in border towns) and thereby significantly affecting the incidence rate in the second jurisdiction, the two jurisdictions may make a disease-specific agreement that the diagnosing jurisdiction does not count the cases but does notify the residence jurisdiction, which will count them.
• Cases moving from one jurisdiction to another while still under surveillance for a notifiable disease are not re-counted in the new jurisdiction.

National analysis and dissemination

PHAC will publish annual surveillance summaries. Provisional data for the most recent notification period will continue to be published each quarter in Canada Communicable Disease Report. Disease incidence and rates of infection will be available on PHAC’’s website under Notifi able Diseases On-Line and can be accessed at the following address: http://dsol-smed.phac-aspc.gc.ca/dsol-smed/ndis/list_e.html

References

1. Doherty J-A. Final report and recommendations from the National Notifiable Diseases Working Group. CCDR 2006;32(19):211-25.
2. Erratum: Final report and recommendations from the National Notifiable Diseases Working Group. CCDR 2008;34:24-5.
3. Advisory Committee on Epidemiology, Division of Disease Surveillance, Bureau of Infectious Diseases. Case definitions for diseases under national surveillance. CCDR 2000;26(S3).

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