Impact of climate and agriculture on enteric illness in Atlantic Canada: toward a climate change adaptation strategy

From 1974 to 1996, Canada experienced over 200 outbreaks of infectious disease associated with drinking water (Charron et al., 2004).  In recent years, large outbreaks of enteric illness caused by E. coli O157:H7 (McQuigge, 2000) and Cryptosporidium  (Hrudey and Hrudey, 2002) have alarmed Canadians and brought demands for political action.  There is mounting evidence that weather is often a factor in triggering waterborne disease outbreaks.  A recent study found that more than half the waterborne disease outbreaks in the United States were preceded by periods of extreme rainfall (Curriero et al., 2001).  High-level precipitation events can create run-off from agricultural land, which can potentially contaminate surface and well waters (Environment Canada, 2001).  An association between agricultural activities and enteric disease incidence has been demonstrated (Valcour et al., 2002; Michel et al, 1999). Current climate change scenarios project that most of Canada will experience longer summers, milder winters and increased summer drought, perhaps punctuated with extreme precipitation events. It is likely that the risk of waterborne illness in Canada will be affected by these changes.

Prince Edward Island has the highest incidence of E.coli O157:H7(1/10,000) in Canada and is 3^rd for reported cases of Campylobacter (Peterson, 2001).  In a 1996 study of sewage and drinking water in Canada, Giardia was detected most frequently in samples from New Brunswick, Nova Scotia and Newfoundland/Labrador (Wallis et al., 1996).  Nova Scotia and Newfound and Labrador also had the highest number of positive samples for Cryptosporidium.  Current climate change scenarios project slight increased summer temperatures, extreme weather events such as storms that bring heavy rainfall, increased thaw and freeze cycles that can cause ice dams and flooding that damage water treatment infrastructure and increased flooding due to sea level rise by the year 2050.  Such changes in climate may have an adverse affect on water quality and health in the Atlantic Provinces (Charron et al.,2004).

The University of Guelph, Health Canada and Environment Canada are working together on a national project investigating the incidence of waterborne illness in Canada, describing the complex relationships between disease incidence, weather parameters, water quality and quantity, and the potential impact that global climate change will have on these parameters.  Several case studies have been identified to examine the relationship between reported waterborne disease outbreaks and extreme weather events.  The case study in the Atlantic Provinces will attempt to answer the following questions:  How much waterborne illness in Atlantic Canada is attributable to agricultural practices?  How much additional waterborne illness can be attributed to climate variability? and How might climate change alter the vulnerability or risk of disease in Atlantic Canada?

The study will describe temporal and spatial trends in cases of enteric illness in Atlantic Canada and examine the relationship between weather parameters (temperature and precipitation) and the number of cases of enteric illness in Atlantic Canada accounting for temporal and spatial clustering. 

  The projected impact of climate change on enteric illness rates will be assessed using climate change scenarios for different time periods (i.e. 10 year, 25 year, 50 year and 100 year projections).  A scenario driven based analysis (i.e. holding all variables steady and varying precipitation over a large range, what would we expect our range of enteric illness to be for different regions of Atlantic Canada) will also be used to assessed to address shorter range impacts and the potential impacts of extreme weather events.

The results of these studies will help identify geographic areas and populations vulnerable to an increased risk of enteric illness.  Climate change scenarios will be applied to the findings to gain a better understanding of how communities in Atlantic Canada may be at increased gastrointestinal vulnerability to the impact of global climate change.  These studies will allow Canadian policy makers to better understand and manage current risks of waterborne enteric illness, and to devise strategies to adapt to an uncertain climatic future and the potential for more extreme weather events.