Communicable disease surveillance : Notification of infectious diseases in Canada

Canada, like many countries. collects and collates aggregate data on communicable diseases nationally. The main objectives of this system are to provide a mechanism for monitoring the health of the population by identifying and responding to changes in reporti ng trends of specific diseases and to provide information that can contribute to the development of health policy and the planning of care, prevention and control programs. These activities function at local, provincial/territorial , and national government levels , focusing on populations rather than individuals. Specific use of national surveillance data includes the identification and control of disease outbreaks; the development and implementation of population-based prevention and control activities and the monitoring of these activities; the production of statistics to aid priority setting; and contributions to international surveil lance activities (I). This paper briefly describes the system by which information on notifiable diseases is collected and collated by the federal government. Information on selected (notifiable) communicable diseases has been collected by the Canadian government since 1924. The Statistics Canada and the Health Canada Acts contain the federal government's mandate to collect these data (2,3) . However, provincial governments enact legislation designed to capture individual reports of cases. The list of diseases for which aggregated nationa l data is collected is subject to change, through recategorization of diseases or enlargement by the addition of new diseases to the list. At present 4 7 diseases are reported to the Bureau of Infectious Diseases, Laboratory Centre for Disease Control (LCDC) in Ottawa (Table 1). A subcommittee convened in 1987 by the national Advisory Committee on Epidemiology (ACE) defined the current list. The list was amended to include hepatitis C in 1991 and a more extensive breakdown of syphilis in 1992.

gate data on communicable diseases nationally.The main objectives of this system are to provide a mechanism for monitoring the health of the population by identifying and responding to cha nges in reporti ng trends of specific diseases and to provide information that can contribute to the development of health policy and the planning of care, prevention and contro l programs.These activities function at local, provincial/territorial , and national govern ment levels , focusing on populations rather than individuals.Specific use of national surve illance data includes the identification and control of disease outbreaks; the development and implementation of population-based prevention and control activities and the monitoring of these activities; the production of statistics to aid priority setting; and contributions to international surveillance activities (I).This paper briefly describes the system by which information on notifiable diseases is collected and collated by the federal government.
Information on selected (notifiable) communicab le diseases has been collected by the Canad ian government since 1924.The Statistics Canada and the Health Canada Acts contain the federal government's mandate to collect these data (2,3) .However, provincial governments enact legislation designed to capture individua l reports of cases.The list of diseases for which aggregated nationa l data is collected is subject to change, through recategorization of diseases or enlargement by the addition of new diseases to the list.At present 4 7 diseases are reported to the Bureau of Infectious Diseases, Laboratory Centre for Disease Control (LCDC) in Ottawa (Table 1).A subcommittee convened in 1987 by the national Advisory Committee on Epidemiology (ACE) defined the current list.The list was amended to include hepatitis C in 1991 and a more extensive breakdown of syphilis in 1992.The Canadian Communicable Disease Surveillance System is based on a close collaboration between LCDC and the epidemiologists responsible for disease control in each province or territory, coordinated by the ACE committee.The goals of the surveillance system as defined by the ACE subcommittee in 1987 were:

Division qf Disease
• To facilitate the prevention and control of the disease under surveillance by identifying prevailing incidence levels, impacts and trends for the development of feasible objectives for prevention and control of the disease and the eva luation of control programs; epidemiological patterns and risk factors associated with the disease to ass ist in the development of intervention strategies; and outbreaks for timely investigation and control.
• To satisfy the needs of government (especially regu latory programs) , health care professionals, voluntary agencies and the public for information about risk patterns and trends in the occurrence of communicable diseases (4) .
Data on notifiable diseases were initially collected and collated by Statistics Canada, but this respons ibility, with the exception of tuberculosis (TB), was transferred to LCDC in 1988.Responsibility for TB data was transferred to LCDC in 1995.The diseases were selected according to 12 criteria designed by the ACE subcommittee to prioritize diseases according to their importance from a nationa l disease survei llance perspective (4).The criteria for which each disease was scored, on an unweighted scale, include World Health Organization interest; necessity for an immed iate public health response; incidence; Agriculture and Agrifood Canada interest; mortality; morbidity; communicabi li ty; case-fatality rate; potential for outbreaks; socioeconomic impact; public perception of risk; and vaccine preventability.
In addition to creating the criteria for prioritizing diseases for inclusion in national surveillance, the ACE subcommittee compiled uniform case definitions for use across Canada which were published as a supplement to Canada Communica-   (5) .It should, however, be noted that for operational reasons, health authorities in provinces or territories may use definitions which differ from those described in the supplement.LCDC publications will note this where it occurs; otherwise it should be assumed that national data on communicable diseases are based on the definitions in the supplement.
The list does not necessarily reflect all the diseases that are required to be reported within each of the jurisdictions.Each province and territory has a wider list of diseases that reflects the priorities of that jurisdiction.

METHOD FOR DATA COllECTION
A generalized method for collection of disease data is illustrated in Figure 1.This scheme may, in reality, vary for some specific diseases, such as AIDS or TB, or by jurisdiction.Genera lly, physicians are required to report clinical diagnoses of a notifiable disease, with or without laboratory confirmation , to their local health authority.This cou ld be a health unit, regional health department or departement sante communautaire.If a case meets the survei ll ance case definition it will be officially reported to the Provincialrrerritorial Health Authority.Cases for which data are incomplete may be further investigated and either confirmed or deleted subsequently.Aggregated age and sex data only are then sent to LCDC for inclusion in national analys is on a regular basis.In addition to the aggregated data, some provinces also report more deta iled 'case-by-case• data for which up to 114 variables could be listed.Local authorities may also receive infor ma tion on appropriate laboratory identifications and will contact the submitting physician to determine whether the isolate or specimen originated from an individual who meets the relevant case definition.Cul tures or specimens from some cases may be referred to national reference laboratories for confirmation of diagnosis, for example, typing of enteric pathogens such as salmonellas.

COLLATION OF DATA AT LCDC
LCDC receives aggregated and case-by-case data on a regular basis from the provincial and territorial health departments; personal identifying information is removed .Data are received , depending on the province or territory and diseasesbased surveillance system , on a monthly, quarterly or annual basis and may be received in electronic (direct transmission or diskette) or paper format.
In addition to variations in the format in which data are received, a survey of provincial and territorial disease surveillance units, conducted during the summer of 1995, found that 14 different computer languages and packages had been used to produce 26 different computerized surveillance systems.The re were also several manual systems in use.The large number of different surveillance programs was not a surprise, since in most jurisdictions, there are up to four different areas responsible for disease surveillance.These are AIDS , TB, sexually transmitted diseases and the other notifiable diseases.Each surveillance area usually has its own system, and many systems were designed and developed by or specifically for a particular unit.This is not true in every province; for example, Ontario has one integrated surveillance system used for all notifiable diseases and conditions.
Coordinating these disparate systems is a major undertaking at the federal level.There is no common format, and there are few common variables.For notifiable diseases (excluding AIDS and TB), of the 114 variables reported case by case by the seven provinces who report most regularly, there are only eight common variables and two of them are mandatory -reporting province and disease.The other common variables are standard demographics relating to sex, age, date of birth , date of report, date of onset and job title/occupation.

DATA OUTPUT FOR LCDC
The notifiable diseases data received by LCDC are currently maintained on a central database and with the exception of AIDS and TB, are analyzed within the Division ofDisease Surveillance.Data are published quarterly in tabular form in the Canada Communicable Disease Report.Detailed annual analyses are published in the Notjfiable Diseases Annual Summaty, the most recent of which was for 1994 (6).This summary provides tabulated data by sex, age and reporting province and territory as well as graphic presentation of information and, increasingly, textual comment on trends.Detailed flies on each notifiable disease are also maintained for use by the division.
Databases are regularly updated, and the information that they contain is used to monitor national trends in communicable diseases and to provide a resource for public health planning and policy making at provincial/territorial and federal government levels.In addition, the information provided by the system is used by researchers in medicine, public health and environmental health, and aggregated data are available upon request.
The national collection of aggregate data through the Notifiable Diseases Reporting System (NDRS) is an essential function that recognizes the value and use of statistics in informed decision-making and policy development.In recognition of this, LCDC has encouraged close collaboration with provincial and territorial epidemiologists and others concerned with public health in the development of NDRS and other national surveillance systems through support of national advisory and technical committees (eg, ACE) and consensus meetings.
To provide the highest quality information, the NDRS must include characteristics that relate to the timeliness with which data pass through the system and emerge as well presented and pertinent information; representativeness of the reported cases, as a subset of both all cases and all exposures to disease; and uniformity of reporting, both in terms of conformity to a given case definition and ensuring that physicians are both aware of what should be notified and that all appropriate cases are notified.
The NDRS is essentially a collaborative effort that incorporates several vital functions, including the primary care provider and the local health unit and laboratory in the recognition and collation of the source data, forming the basis of the NDRS ; the provincial/territorial health department, which collates and sends aggregate and case-by-case data to LCDC; provincial public health and national reference laboratories, which provide essential expertise in the identification of disease agents; and LCDC, where national data is collated, analyzed and published .Future improvement of the system will depend on continued encouragement to report disease as well as the development of the electronic means to collect, collate and move data at all levels.

ADDENDUM
The case definitions supplement is available free of charge by contacting Sheila Herman, Division of Disease Surveillance, Laboratory Centre for Disease Control, PL 0603EI -3rd Floor LCDC Building, Health Canada, Tunney's Pasture, Ottawa, Ontario, KIA OL2, telephone 613-952-8227 or fax 613-998-6413.The 1994 Notifiable Diseases Annual Summary is available free of charge by contacting Carole Scott, Division of Disease Surveillance, Laboratory Centre for Disease Control, PL 0603E 1, 3rd Floor LCDC Building, Health Canada, Tunney's Pasture, Ottawa, Ontario KIA OL2 , telephone 613-957-0334 or fax 613-998-6413.

TABLE 1
* Where reporting stopped, for whatever reason, the dates indica te period and then year when reports were aga in received.' Previously repo rted as nongonococcal, nonsyphilitic VD. 'Gaps appear which reflect changes in reporting practice for these diseases .§O riginally reported as 'infective jaundice ' or 'hepatitis '. 'Originally reported aggregated as 'encephalitis' or