Most foodborne outbreak investigations (63.5%) reported a specific food, most frequently meat.
The analysis summarizes foodborne outbreak investigations reported to the Outbreak Summaries (OS) Reporting System between 2008 and 2014.
It covers etiological agent, severity of illness, outbreak duration, exposure setting and source. It was the first national-level summary of outbreaks reported through the OS Reporting System.
A total of 115 reported foodborne outbreaks were included which represents 11.2% in the enteric module of the OS Reporting System between 2008 and 2014, making them the second most common mode of transmission for enteric outbreaks, after person-to-person transmission.
British Columbia (BC) reported more than half of the foodborne outbreaks in the system (58.3%).
It is estimated four million episodes of domestically acquired foodborne illness occur every year in Canada, according to a 2013-study by Thomas MK et al.
Salmonella was the most commonly reported cause (40.9%) and Enteritidis was the most common serotype.
Other etiologic agents were Escherichia (14.8%) and norovirus (12.2%). All reported Escherichia outbreaks were caused by E. coli O157 VTEC.
Under diagnosis and lack of laboratory confirmation for some infections like Campylobacter and toxins, as well as under-reporting and variable investigation practices for these pathogens may explain why these pathogens are not ranked as high in the OS Reporting System, said the researchers.
Enteric outbreak investigation is performed at local, provincial/territorial (P/T) and federal levels.
Routine surveillance did not occur in the past in many jurisdictions and in response to this information gap and the need for an outbreak surveillance system, the Public Health Agency of Canada (PHAC) partnered with P/T public health authorities in 2008 to create the Outbreak Summaries (OS) Reporting System.
The web-based application has two modules: one for enteric, foodborne and waterborne diseases and one for respiratory and vaccine-preventable diseases.
Six provinces (British Columbia, Manitoba, Ontario, Nova Scotia, Prince Edward Island and Newfoundland and Labrador) and the Centre for Food-borne, Environmental and Zoonotic Infectious Diseases (CFEZID) at PHAC have implemented the enteric module of the OS Reporting System and routinely report outbreaks.
Over the study period, the proportions of Salmonella outbreaks decreased sharply in 2011 and 2012 and were mainly reported by BC and PHAC.
During the same period, PHAC encountered a proportional increase in E. coli-related outbreaks.
Known etiologic agents that caused the greatest number of cases per outbreak were Salmonella, Cyclospora, Clostridium perfringens and shellfish poisoning with an average of 43, 40, 37 and 33 cases per outbreak respectively.
Hospitalizations and deaths
Infections due to Salmonella and E. coli accounted for the majority of hospitalizations (106 and 84 respectively). Salmonella had an average hospitalization proportion of 12% while E. coli had an average of 41.8%.
Clostridium botulinum, Listeria and histamine poisoning had the highest hospitalization proportions with 100%, 90%, and 75% respectively.
Listeria was the most common cause of outbreak-related deaths, accounting for 73.3% of total deaths (22/30). The case fatality ratio was 32.8% among outbreak-related cases.
All 22 Listeria-related-deaths reported in the OS Reporting System were during the same outbreak and involved immune-compromised and elderly individuals, most of whom were in hospitals or long term care facilities during the exposure period.
Most investigations (63.5%) reported a specific food associated with the outbreak. Meat was the most commonly reported source (26%), followed by eggs (15.1%) and vegetables (13.7%).
Researchers said the strength of the system is that it provides a source of data to monitor occurrence and trends in enteric, foodborne and waterborne disease outbreaks at national level.
“It provides F/P/T partners with a system that allows them to collect, query and summarize outbreak information in a systematic and standardized manner,” they said.
“These data have been used to support hypothesis generation in outbreak investigations led by PHAC and by participating jurisdictions for their own internal reporting and outbreak investigations.
“Future efforts will focus on continuing to enhance national representativeness by enrolling additional provinces and territories in the OS Reporting System.
“Finally, existing data fields are undergoing review and additional variables are anticipated that will improve the description and characterization of outbreaks.”
Source: Canada Communicable Disease Report (CCDR)
Authors: Bélanger P, Tanguay F, Hamel M, Phypers M