Overall description of reported cases
From 2007 to 2009, 29,897 gastrointestinal illnesses (GI) were reported by 36 local health authorities in Ontario. Of these, 20,062 (67.1%) were successfully followed up by public health. Figure is a flow diagram of the various exclusions for all GI cases. Table shows the proportion of cases not followed up by public health, as well as cases with multiple or unclear exposure information by disease. Amebiasis (54.3%), giardiasis (39.4%), and campylobacteriosis (39.1%) had the highest proportion of cases which were not successfully followed up.
Flow diagram of status of reported gastrointestinal illnesses in Ontario between 2007 and 2009.
Proportion of gastrointestinal illnesses excluded from source attribution analyses
Table shows the number of reported cases and incidence by year. The most frequently reported GI were campylobacteriosis (10,916), salmonellosis (7,514) and giardiasis (4,726), which together accounted for 61.6% of all GI reported from 2007 to 2009. The proportion of cases attributed to travel and outbreaks, as well as the proportion of hospitalizations and deaths is shown in Table . Overall, 27.6% of GI cases were travel-related, having travelled outside of Ontario at any time during the relevant incubation period. The diseases with the highest proportion of cases related to travel were typhoid fever (87.1%), paratyphoid fever (85.1%), and cyclosporiasis (61.6%); the diseases with the lowest proportion of travel-related cases were botulism (0.0%), listeriosis (4.4%), and VTEC-illness (7.8%).
Reportable gastrointestinal illnesses in Ontario by year, between 2007 and 2009
Reportable gastrointestinal illnesses in Ontario by travel, outbreak, hospitalization, and mortality, between 2007 and 2009
During this period, 75 outbreaks were reported. While these outbreaks were mostly due to salmonellosis (n=32 outbreaks, 460 cases), VTEC-illness (n=18 outbreaks, 172 cases) and campylobacteriosis (n=10 outbreaks, 72 cases), the highest proportion of outbreak-related cases were for listeriosis (37.6%, 71 cases) and VTEC-illness (22.6%, 172 cases). Hospitalization of more than 40% of reported cases was documented for listeriosis (60.8%), botulism (60.0%), and typhoid fever (44.4%). While the overall proportion of deaths for all GI combined was 0.4% (n=126), 24.3% (n= 46) of reported listeriosis cases died.
Demographics of reported cases
Figure shows the age-specific incidence grouped by diseases with similar incidence levels. The highest age-specific incidence for salmonellosis and yersiniosis was in those under 1 year of age (Figure -A and 2-D). The highest incidence for campylobacteriosis, cryptosporidiosis, VTEC-illness, shigellosis, and giardiasis was in those aged 1–4, with shigellosis and giardiasis exhibiting a second, albeit lower peak in the 25–44 age group (Figure ). Amebiasis and cyclosporiasis peaked in adults aged 25–44 and 45–64, respectively (Figure -B and 2-C). Listeriosis incidence was highest in those over 65 years of age, as well as in those under one year of age (Figure -C). The highest age-specific incidence for hepatitis A was in the 5–14 year age group (Figure -C).
Figure 2 Incidence of reportable gastrointestinal illnesses in Ontario by age group between 2007 and 2009 (N=29,449).A: campylobacteriosis (n=10,901) and salmonellosis (n=7,507); B: amebiasis (n=2,134), cryptosporidiosis (n=1,046), verotoxigenic Escherichia coli (more ...)
Overall, significantly more GI cases occurred among males than females (54.8%, p<0.001). Males accounted for significantly more cases of amebiasis (71.1%, p<0.001), campylobacteriosis (55.0%, p<0.001), giardiasis (58.8%, p<0.001), shigellosis (57.2%, p<0.001), and yersiniosis (54.4%, p=0.02). There were significantly fewer male VTEC-illness cases (45.3%, p=0.01) and no significant sex differences were found for botulism, cryptosporidiosis, cyclosporiasis, hepatitis A, listeriosis, paratyphoid fever, salmonellosis, and typhoid fever.
Exposures of domestic sporadic cases
Domestic sporadic cases that were successfully followed up by public health accounted for 44.6% (13,341/29,897) of all reported cases, and 70.1% (13,341/19,043) of all cases with exposures (Figure ). Overall, 26.0% of primary exposure sources and 15.4% of primary exposure settings for domestic sporadic cases were known, with VTEC-illness having the highest proportion of known sources (40.7%) and settings (27.3%) of all diseases (Table ).
Sporadic domestic reportable gastrointestinal illnesses in Ontario by known or unknown exposure between 2007 and 2009
Among cases with known exposures, the most common sources were food (54.2%), animals (19.8%), and contact with an ill person (16.9%). Private homes (45.5%) and food premises (29.7%) were the most common exposure settings (Table ). Among cases exposed in private homes (n=937), the most frequently reported sources were food (62.6%), followed by contact with animals (21.1%) and contact with persons ill with similar symptoms (13.1%). For cases exposed in food premises (n=611), the most frequently reported source was food (96.1%). Among cases exposed in settings other than private homes and food premises (n=510), the top exposure sources were contact with animals (38.0%), water (28.8%), and food (26.7%).
Sporadic domestic reportable gastrointestinal illnesses in Ontario by exposure source and setting between 2007 and 2009
Seasonality of domestic sporadic and travel cases
Domestic cases of campylobacteriosis, cryptosporidiosis, giardiasis, salmonellosis, and VTEC-illness showed seasonal patterns with incidence peaking in the summer months (Figure ). For all these diseases, modest concurrent summer increases were also observed among travel-related cases with the exception of VTEC-illness. Additional peaks in travel-related cases in the winter for campylobacteriosis and giardiasis, and in early spring for salmonellosis, amebiasis, typhoid fever and yersiniosis were also observed (Figures and ). Cyclosporiasis was the only disease that showed a late spring/early summer peak in travel-related cases. Summer to early fall peaks were apparent in travel-related cases of shigellosis, hepatitis A and typhoid fever. Smaller peaks in January were seen in travel-related cases for most diseases (Figures and ).
Figure 3 Domestic and travel-related gastrointestinal illnesses in Ontario with pronounced domestic seasonal patterns. Mean monthly number of sporadic domestic and travel-related reportable GI in Ontario with pronounced domestic seasonal patterns by travel status (more ...)
Figure 4 Domestic and travel-related gastrointestinal illnesses in Ontario with many travel-related cases or without pronounced domestic seasonality. Mean monthly number of sporadic domestic and travel-related reportable GI in Ontario with a high proportion of (more ...)