ARCHIVED - Canadian National Report on Immunization, 2006

Volume: 32S3 - November 2006

3. Vaccine-preventable Disease Surveillance Systems

Surveillance is the systematic, ongoing collection, collation and analysis of data and the timely dissemination of information to those who need to know so that action can be taken ⁷. Surveillance may be established to assess the public health status of a health event, establish public health priorities, evaluate programs and contribute to hypothesis generation and research ⁸. A number of criteria can be used to determine conditions that should be under surveillance, such as incidence, severity, changing epidemiologic patterns, socio-economic burden, risk perception and preventability ⁹. In Canada, most vaccine-preventable diseases are under surveillance by one or more national systems. This section describes the national surveillance systems that monitor vaccine-preventable diseases, including enhanced disease-specific systems coordinated by IRID.

3.1 Notifiable Diseases Reporting System (NDRS)

The NDRS is the passive surveillance system coordinated by PHAC that is used to monitor more than 40 nationally notifiable infectious diseases. The objectives of disease surveillance by the NDRS are to

1. facilitate the control of the disease under surveillance by identifying

   1. prevailing incidence levels, impacts 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. satisfy the needs of government, health care professionals, voluntary agencies and the public for information on risk patterns and trends in the occurrence of communicable diseases.

Case definitions for diseases under national surveillance were published as a CCDR supplement in 2000 ¹⁰. Physicians, hospitals and/or laboratories report cases of specific diseases to P/T departments of health as mandated by P/T legislation. P/T health authorities determine whether the case meets the surveillance case definition and, if so, gather the necessary epidemiologic data on it. Non-nominal data on notifiable cases are submitted to the NDRS using a “core set” of variables. Data entry and analysis occur at PHAC. Provisional data are published quarterly in the CCDR, and finalized numbers of cases and incidence rates are published in annual surveillance summaries and on-line at: http://dsol-smed.phac-aspc.gc.ca/dsol-smed/ndis/index_e.html.

3.2 Enhanced measles surveillance

The enhanced measles surveillance system was modified in 1998 to an email-based reporting system. Every week, when prompted, P/T reply by email to IRID. If there are no cases, then they reply with no comment; if there is a case that meets the national case definition, a case report is completed and attached. The variables collected include demographic data, immunization history and exposure history. The weekly response rates for 13 provinces and territories averaged around 70% for 2004 and 62% for 2005.

3.3 Enhanced invasive meningococcal disease (IMD) surveillance

Enhanced case-based surveillance has been conducted by IRID since 1985. P/T departments of health report non-nominal epidemiologic data on all IMD meeting the national case definition, at a minimum, on a yearly basis. P/T public health and/or hospital laboratories send most Neisseria meningitidis isolates to the National Microbiology Laboratory in Winnipeg for confirmation of serogroup and further bacteriologic studies (serotyping and subtyping for all isolates and multilocus enzyme electrophoresis for all serogroup C isolates). Probabilistic matching on P/T, date of birth (or age), sex, onset date and serogroup (when available) is conducted to retrospectively link epidemiologic and laboratory data for those P/T not able to pre-link the data¹¹.

3.4 FluWatch

IRID maintains a national influenza surveillance network through the FluWatch program. Each week, IRID collects, collates and analyzes national influenza and influenza-like illness (ILI) data provided by its surveillance partners. The primary objectives of FluWatch, first initiated in 1996-97, are early detection and monitoring of influenza outbreaks; provision of timely updates on influenza activity in Canada and abroad to public health professionals as well as the public; rapid detection and monitoring of circulating strains of influenza viruses, including new sub-types; and contribution to global information on circulating virus strains to assist decision-making concerning vaccine composition for the following season. FluWatch has five main components:

1. Laboratory-confirmed influenza detections: approximately 33 sentinel laboratories across Canada report the total number of laboratory tests conducted each week and the number of specimens positive for influenza by virus type to the Respiratory Virus Detection Surveillance System (RVDSS).

2. Influenza virus characterization: the National Microbiology Laboratory analyzes a proportion of positive influenza specimens tested by provincial laboratories and provides strain information on circulating influenza viruses.

3. ILI consultation rates: each year, approximately 250 sentinel physicians are recruited through the National Research System of the College of Family Physicians of Canada (from seven provinces and three territories) and by independent sentinel provincial programs (in British Columbia, Alberta and Saskatchewan). Between 70% and 90% of sentinels report weekly during the regular influenza season (September to April), and participation declines during the summer months. A standard case definition for ILI is used, and patients meeting the definition are determined as a proportion of all patient consultations for all reasons during 1 day of each week. These numbers are then aggregated, and an average national ILI consultation rate is produced.

4. Influenza activity level assessment: P/T epidemiologists assess regional influenza activity levels based on ILI data, laboratory detections and outbreaks in long-term care facilities, schools and hospitals. Regional activity levels are classified as no activity, sporadic, localized or widespread.

5. Sentinel monitoring of pediatric hospitalizations due to influenza: beginning in the 2003-2004 influenza season, a pilot study was initiated with the Immunization Monitoring Program, ACTive (IMPACT) network of pediatric hospitals to determine the feasibility of hospital-based surveillance of laboratoryconfirmed influenza admissions and mortality in children. The pilot was incorporated into the Flu Watch surveillance system as a key indicator of severity of influenza in children in autumn 2003¹².

3.5 IMPACT

The IMPACT network has been actively monitoring vaccine-preventable diseases since 1991 and vaccine-associated adverse events since 1993. The network currently includes 12 pediatric tertiary care centres in eight provinces that receive referrals from all P/T. IMPACT centres account for approximately 90,000 admissions every year and represent about 90% of all tertiary care pediatric beds in Canada. Nurse monitors at each IMPACT site review laboratory reports and admission and discharge records to identify cases, and they complete detailed case report forms. The nurse monitor is assisted by team members such as infection control nurses, emergency and unit nurses, physicians, laboratory personnel and medical records staff. Each centre also communicates with the local public health department and the provincial epidemiologist to report cases, distribute IMPACT news, and collect immunization histories and other data specific to each centre. Information on each case reported through the IMPACT network is sent to the Vaccine Evaluation Centre in Vancouver, BC, where data are entered, cleaned and analyzed. IMPACT is administered by the Canadian Paediatric Society (CPS) with 11 centres receiving funding from IRID¹³.

3.6 Canadian Paediatric Surveillance Program (CPSP)

In January 1996, the CPSP was initiated to look for rare childhood conditions, including congenital rubella syndrome and acute flaccid paralysis. The CPSP uses a two-tiered reporting process to ascertain and investigate cases. Approximately 2,400 practising pediatricians and pediatric sub-specialists are asked to complete monthly initial report forms regardless of whether they see a case or not. Participants who report cases are asked to submit detailed report forms. Case ascertainment is monitored and verified by investigating duplicate reports and comparing data with relevant programs and centres, including IMPACT and the NDRS. Once the detailed report has been returned to the CPSP, it is forwarded to the investigator for analysis. The overall response rate for the initial report forms has remained stable at 81% to 83% since 1999, with completion rates of detailed questionnaires for reported cases higher, at approximately 95%¹⁴.

3.7 International Circumpolar Surveillance (ICS)

ICS is a population-based invasive bacterial disease surveillance network of circumpolar countries (Canada, Finland, Greenland, Iceland, Norway, Sweden and United States). Within Canada, five regions (Yukon, Northwest Territories, Nunavut, and the northern regions of Labrador and Quebec) and a network of 14 laboratories, including three references laboratories (the Laboratoire de santé publique du Québec, the National Streptococcus Centre and the National Microbiology Laboratory), participate in the ICS initiative. Communicable disease consultants located in the five regions gather clinical and demographic information on reported cases. Laboratory and clinical data are forwarded in “real-time” to the ICS coordinator at the Arctic Investigations Program of the United States Centers for Disease Control and Prevention in Anchorage, Alaska. ICS data contribute to the understanding of the epidemiology of invasive bacterial diseases among northern populations, and this assists in the formulation of prevention and control strategies for these populations, including immunization recommendations. Canada, through IRID, has been a partner since 1999¹⁵.

The vaccine-preventable diseases under surveillance by these systems are shown in Table 3.

Table 3. National surveillance systems monitoring vaccine-preventable diseases in Canada