Enteric surveillance and outbreak detection

 Day 1: Monday July 21, 2014

You are a federal epidemiologist working for the Public Health Agency of Canada (PHAC). On Monday July 21, you attend your weekly meeting to review the National Enteric Surveillance Program (NESP) numbers from the previous week (July 13 to 19, NESP Week 2014-29).

The NESP provides timely analysis and reporting for laboratory-confirmed isolations of enteric pathogens in Canada, including bacteria, viruses and parasites. Provincial public health laboratories submit aggregate counts of enteric pathogens, including genus, species, and serotype information, on a weekly basis. Organisms are reported at the serotype level on a weekly basis by the provincial public health laboratories. The NESP is administered by the Public Health Agency of Canada (PHAC) and surveillance data are disseminated to federal, provincial/territorial, and local stakeholders through the weekly NESP report, other summary reports, and web-based applications.

The NESP numbers of confirmed E. coli O157 cases are summarized in Table 1 below. E. coli O157 numbers are significantly above expected nationally (17 cases reported, 12 expected) as well as provincially in Saskatchewan (2 cases reported, 0 expected) and Manitoba (3 cases reported, 0 expected). Numbers are within expected levels for all other provinces.

Table 1: NESP numbers of confirmed E. coli O157 cases, by province, Week 2014-29* (July 13-19, 2014)

Jurisdiction Reported Expected Significantly higher than expected?
National 17 12 Yes
British Columbia 1 1 No
Alberta 3 3 No
Saskatchewan 2 0 Yes
Manitoba 3 0 Yes
Ontario 5 6 No
Quebec 3 2 No
New Brunswick 0 0 No
Nova Scotia 0 0 No
Newfoundland and Labrador 0 0 No
Prince Edward Island 0 0 No
Yukon 0 0 No
Northwest Territories 0 0 No
Nunavut 0 0 No

*There is a brief interval between the isolation/identification of organisms and routine reporting to NESP, as such the timelines for detection of increases in reported case counts used in this case study are not reflective of the actual timeline for analysis of NESP weekly data.

Note: The reported and expected case counts in the table above are fictitious and have been created for the sole purpose of this case study.  They do not represent actual case counts at the national or provincial level, and no interpretation or conclusion can be inferred. These data should not be further published or distributed beyond the educational limits of this case study.

Question 1-1: What are the main limitations of this surveillance system? What is a potential next step for determining if any of these cases may be related?

 

 

ANSWER
  • Limitations of the NESP
    • Underreporting: Like all laboratory-based surveillance systems, the NESP only includes laboratory-confirmed cases. People who did not seek medical attention, or who did not have a specimen taken for testing, will not be captured. Furthermore, not all specimens/isolates are referred from the regional and local laboratories to the provincial public health laboratories; therefore, some organisms are under-represented in the NESP, such as Campylobacter, enteric parasites, and viruses.
    • Specificity: The NESP captures serotype level information only – unless the serotype is rare, additional sub-typing is likely needed to determine if the cases are related.
  • Potential next steps:

 

 

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