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May 2008 Volume 34 Number 05
MK Thomas, MSc (1,2), SE Majowicz, MSc, PhD (1,2), F Pollari, DVM, MPH, DVSc (1), PN Sockett, PhD (1,2)
The National Studies on Acute Gastrointestinal Illness (NSAGI) initiative was designed to generate baseline period prevalence rates of self-reported AGI in communities across Canada, assess the burden associated with AGI, and quantify the under-reporting of AGI in Canada's national enteric disease reporting systems.
Methods utilized included population surveys administered randomly via telephone services. Three population surveys in three locations within Canada included over 10,000 residents. Questions pertained to recent symptoms as well as socio-demographic factors, use of the health care system and missed work or school due to illness.
In summary of published results, there are an estimated 1.3 episodes of AGI per person-year and an estimated 10-47, 13-37 and 23-49 cases in the community for every case of verotoxigenic Escherichia coli, Salmonella and Campylobacter, respectively, captured within the national surveillance system. AGI represents an annual per capita cost of $115 CAD.
The work of NSAGI highlights the significant burden and impact of AGI in the Canadian population. These results will also be incorporated into the current work at the World Health Organization (WHO) to estimate the global burden of food related illnesses.
Acute gastrointestinal illness (AGI) is a global problem with mortality and morbidity affecting both developed and developing countries. It is caused by a variety of agents, and is frequently transmitted by food or water. Symptoms typically include diarrhea or vomiting, with additional secondary symptoms which frequently include fever, cramps, nausea and headache.
Increased understanding of the transmission of enteric pathogens has lead to regulations and intervention programs to control or prevent disease and sustained surveillance activities to monitor disease trends. However, with increased globalization, travel and trade, and impacts of climate change, among other factors, continued research activities are needed to address new or potential risks and their mitigation.
The Public Health Agency of Canada (PHAC) developed the National Studies on Acute Gastrointestinal Illness (NSAGI) initiative in 1999 to address the information gaps that existed on the magnitude, distribution and burden of AGI in Canada. The overall goals for the initiative included: generating baseline period prevalence rates of self-reported AGI in communities across Canada; assessing the socio-economic burden of illness associated with AGI; describing and quantifying the under-reporting of AGI in Canada's national enteric disease reporting systems and developing studies to further understanding of risk factors and chronic sequelae associated with AGI in Canada. The ultimate aim of these studies is to decrease the magnitude and burden of AGI in Canada through the development of specific and measurable interventions(1). To date the approaches taken have included population telephone surveys, a national laboratory survey and regional physician surveys. This article summarizes the key findings from the population surveys and details plans for future activities, as part of PHAC's initiatives related to AGI in the Canadian population.
Since its inception, NSAGI has successfully completed three, 12-month population surveys administered by telephone to randomly selected respondents, in three locations within Canada: (1) Hamilton Ontario(2), (2) three regions of British Columbia (BC)(3), and (3) the province of Ontario(4). The Hamilton study was conducted from February 2001 to February 2002 and surveyed 3,496 residents. The BC study was conducted from June 2002 to June 2003 and surveyed 4,612 residents. The Ontario study was conducted from May 2005 to May 2006 and surveyed 2,090 residents.
In these surveys of representative population samples, a broad case definition was adopted to be highly sensitive to capturing cases of AGI. Individuals were defined as cases if they had experienced symptoms of vomiting or diarrhea in the previous 28 days. ‘Vomiting' was described as the forcible expulsion of the contents of the stomach out of the body while ‘diarrhea' was defined as stool with abnormal liquidity or any loose stool. Individuals with pre-existing conditions or illnesses, as diagnosed by a medical doctor, with vomiting and diarrhea as a common symptom were excluded from being cases but included as non-cases.
Under-reporting and cost
Data from the population surveys were combined with various other data to generate estimates of the cost and under-reporting of AGI, as well as pathogen-specific under-reporting estimates. Detailed methods are available(5-8).
Results of the Hamilton study have been reported in detail elsewhere. Briefly, of the 3,496 respondents, 351 were identified as cases of AGI, yielding a monthly prevalence of 10.0% (95% CI = 9.9 to 10.1) and an annual incidence rate of 1.3 (95% CI = 1.1 to 1.4) episodes per person-year. A significantly (p < 0.05) higher prevalence was observed among female respondents (12%) compared to male respondents (9%). Higher prevalence was observed in those < 10 years of age and among those 20 to 24 years of age (Figure 1). Seasonal peaks occurred around April and October (Figure 2).
British Columbia study
Results of the BC study have been reported in detail elsewhere. Briefly, of the 4,612 respondents, 451 were identified as cases of AGI, yielding a monthly prevalence of 9.8% (95% CI = 8.9 to 10.6) and an annual incidence rate of 1.3 (95% CI = 1.1 to 1.4) episodes per person-year. A significantly (p < 0.05) higher prevalence was seen among female respondents (11%) compared to male respondents (9%). Higher prevalence was observed in those < 15 years of age (Figure 1). Seasonal peaks occurred during winter and summer months (Figure 2).
Figure 3: Calculations used to determine approximate number of episodes of foodborne disease in Canada annually
1.3 episodes of AGI per person-year
X 32 million Canadians =
Results of the Ontario study have been reported in detail elsewhere. Briefly, of the 2,090 respondents, 179 were identified as cases of AGI, yielding a monthly prevalence of 8.6% (95% CI = 7.4 to 9.8) and an annual incidence rate of 1.2 (95% CI = 0.99 to 1.4) episodes per person-year. A marginally significant (p = 0.08) higher prevalence was observed among female respondents (9%) compared to male respondents (7%). Higher prevalence was observed in those < 10 years of age (Figure 1). A seasonal peak occurred between February and April (Figure 2).
For each case of AGI reported in Ontario(5) and British Columbia(6), an estimated 313 and 347 cases occur in the community, respectively. Additionally, AGI represents an annual per capita cost of $115 CAD(7) related to healthcare and lost productivity, based on the Hamilton study(2). The largest cost component is missed paid employment by individuals with AGI and their caretakers taking time away from paid employment. If this number is generalized to the entire Canadian population, the estimated annual cost of AGI in Canada would be $3.7 billion CAD. However, due to potential geographical differences more studies are needed to provide a more accurate cost for the Canadian population.
It was estimated that for every case of verotoxigenic Escherichia coli, Salmonella and Campylobacter there are approximately 10-47, 13-37 and 23-49 cases respectively, in the Canadian population, circa 2000(8). Costs associated with cases due to specific pathogens have not yet been estimated for Canada.
The results presented here highlight the significant burden and impact of AGI to the Canadian population, and are an overview of some of the NSAGI results to date. They illustrate the impact of AGI in Canada and provide comparisons to other countries. Overall the incidence and distribution of AGI in Canada are comparable to estimates from other studies conducted in Ireland, the Netherlands, the United States and Australia(9-12).
Building on these estimates of AGI will be to determine the specific incidence and burden due to foodborne causes. By extrapolating the results of studies published in 1999 from the United States(13), where 75% of AGI is estimated to be related to an enteric infection versus 25% due to a respiratory infection, and an estimated 36% of these enteric infections are related to food, a plausible estimate of the number of cases of foodborne disease in Canada can be generated. Assuming an annual incidence of AGI of 1.3 episodes per person-year, it is estimated that approximately 11 million episodes of foodborne disease occur each year in Canada (Figure 3). This estimate would likely contain a full range of symptoms and severity and include a high proportion of individuals with relatively mild illness. Current initiatives, such as C-EnterNet(14) are needed to more fully describe the burden of disease due to foods and food-pathogen combinations.
To fully comprehend the burden of AGI, further work is needed to investigate the impact of long-term sequelae caused by AGI as well as to investigate, in detail, reasons for and regional differences in, under-reporting of illness to public health authorities. The WHO is working to estimate the global burden of food related illnesses using disability adjusted life years (DALYs) and will be including the impact of long-term sequelae caused by infection with specific enteric pathogens(15). The results from NSAGI will be incorporated in these estimates.
The results presented here are an interim summary of the NSAGI activities to date. There are several NSAGI activities in progress or being planned that will contribute to the epidemiology of AGI in Canada. These include the following: The Quebec population survey will determine the population incidence and distribution of AGI in defined regions of the province as well as examine the relationship between AGI and agriculture and climate change risk factors. The Community Etiology study will determine the pathogen specific incidence and distribution of AGI in Canada. In collaboration with the WHO project mentioned above, the Burden of Foodborne Disease study will determine the morbidity, mortality and cost in Canada, of pathogens commonly transmitted by food. Once these projects are complete, efforts will continue to assess the chronic sequelae and risk factors associated with AGI in Canada.
The authors would like to thank, PHAC NSAGI team, British Columbia Centre for Disease Control NSAGI team, Ontario Ministry of Health and Long Term Care, National Notifiable Disease Registry, University of Guelph, McMaster University, the National Microbiology Laboratory, the Laboratory for Foodborne Zoonoses and the Centre for Foodborne, Environmental and Zoonotic Infectious Diseases.