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Detailed epidemiologic examination of the distribution of Kawasaki disease (KD) cases could help elucidate the etiology and pathogenesis of this puzzling condition. Location of residence at KD admission was obtained for patients diagnosed in Canada (excluding Quebec) between March 2004 and March 2015. We identified 4,839 patients, 164 of whom (3.4%) developed a coronary artery aneurysm (CAA). A spatiotemporal clustering analysis was performed to determine whether non-random clusters emerged in the distributions of KD and CAA cases. A high-incidence KD cluster occurred in Toronto, ON, between October 2004 and May 2005 (116 cases; relative risk (RR) = 3.43; p

Background We have previously documented an increase in the incidence of Kawasaki disease (KD) in Ontario followed by a stabilization from 1995 to 2006. We sought to validate the estimation of incidence of KD using administrative data and to describe the epidemiology of KD across Canada from 2004 to 2014. Methods We queried the Canadian Hospital Discharge Database for hospital admissions associated with a discharge diagnosis of KD. The data set was manually curated and estimates of incidence were compared with those obtained from the retrospective triennial surveillances of KD performed in 2007 and 2010. Results The average number of cases per year identified through administrative data was 245 ± 45 vs 229 ± 33 from retrospective surveillance. This overestimation, representing 7 ± 6%, is similar to the historical percentage of patients originally diagnosed with KD in whom the diagnosis is subsequently excluded. The annual incidence of KD in Canada was 19.6, 6.4, and 1.3 cases per 100,000 children younger than 5 years, 5-9 years, and 10-14 years old, respectively, with important regional and seasonal differences. The incidence remained stable over the study period in the youngest age group but increased in both older age categories. Coronary artery aneurysms affected 3.5% of all patients, and 0.8% experienced associated major cardiac complications. Conclusions Reliance on administrative data to determine incidence of KD is feasible and accurate with manual curation of the data. The incidence of KD in Canada seems to have plateaued for younger children. Differences in annual incidence observed between provinces remain to be explained, and might reflect genetic or environmental differences.

Background The pathogenesis of Kawasaki disease (KD) is commonly ascribed to an exaggerated immunologic response to an unidentified environmental or infectious trigger in susceptible children. A comprehensive framework linking epidemiological data and global distribution of KD has not yet been proposed. Methods and findings Patients with KD (n = 81) were enrolled within 6 weeks of diagnosis along with control subjects (n = 87). All completed an extensive epidemiological questionnaire. Geographic localization software characterized the subjects’ neighborhood. KD incidence was compared to atmospheric biological particles counts and winds patterns. These data were used to create a comprehensive risk framework for KD, which we tested against published data on the global distribution. Compared to controls, patients with KD were more likely to be of Asian ancestry and were more likely to live in an environment with low exposure to environmental allergens. Higher atmospheric counts of biological particles other than fungus/spores were associated with a temporal reduction in incidence of KD. Finally, westerly winds were associated with increased fungal particles in the atmosphere and increased incidence of KD over the Greater Toronto Area. Our proposed framework was able to explain approximately 80% of the variation in the global distribution of KD. The main limitations of the study are that the majority of data used in this study are limited to the Canadian context and our proposed disease framework is theoretical and circumstantial rather than the result of a single simulation. Conclusions Our proposed etiologic framework incorporates the 1) proportion of population that are genetically susceptible; 2) modulation of risk, determined by habitual exposure to environmental allergens, seasonal variations of atmospheric biological particles and contact with infectious diseases; and 3) exposure to the putative trigger. Future modelling of individual risk and global distribution will be strengthened by taking into consideration all of these non-traditional elements.

Introduction: Historically, 2 methods have been used to determine the incidence of Kawasaki disease (KD): active or passive surveillance, or the use of administrative databases. Given the increasing regulatory requirements, mainly around patient privacy, periodic retrospective surveillances have become increasingly challenging. Administrative databases are not curated datasets and doubts have been cast on their accuracy. Methods: The Hospital for Sick Children has been conducting retrospective triennial surveillances of KD since 1995 by contacting all hospitals in Ontario and manually reviewing all cases through chart review, reconciling inter-hospital transfers and multiple readmissions. We queried the Canadian hospital discharge database (Canadian Institute for Health Information) for hospitalizations associated with a diagnosis of KD between 2004-9. The administrative dataset was manually reviewed; patient national health number, institution and dates of admission/discharge were used to identify inter-hospital transfers, readmission and follow-up episodes. Results: The Canadian hospital discharge database reported 1,685 admissions during the study period (281±44 per year) for Ontario. Manual review of the dataset identified 219 (13%) as inter-hospital transfers (56, 26%), readmissions (122, 56%), admissions for follow-up of coronary artery aneurysms (14, 6%) or hospital admissions not related to KD (27, 12%). When these admissions were removed, the total number of incident cases for the study period was 1,466 (244±45 per year). The retrospective triennial surveillance identified 1,373 KD cases during the same period (229±33 per year). The Canadian hospital discharge database overestimated the number of cases in all 6 years by an average of 6.7±5.9%. The overestimation likely comes from patients who were originally diagnosed with KD but in whom the diagnosis of KD was subsequently excluded (historically ~5-6%). Conclusions: Reliance on administrative data to determine incidence of KD is possible and accurate; data should be manually reviewed to remove non-incident cases and estimates should be adjusted to reflect the expected proportion of patients in whom the diagnosis of KD will be subsequently excluded.

Introduction: We have previously documented in consecutive triennial systematic surveillances a rise in the incidence of KD in Ontario, Canada between 1995 and 2004 followed by a stabilization at 24-26 cases per 100,000 children Methods: We queried the Canadian hospital discharge database (Canadian Institute for Health Information) for hospital admissions associated with a discharge diagnosis of KD (either primary or secondary) between 2004 and 2011. Multiple admissions for a given patient were not counted as separate incident cases unless >2 months from the original admission and associated with IVIG treatment. Denominators were derived from population data from the 2001, 2006 and 2011 Censuses. Results: The annual incidence of KD during the study period was 21.9, 6.8 and 1.1 cases per 100,000 children Conclusions: The previous increase in the incidence of KD has plateaued, indicating that the true annual incidence fluctuates between 20-22 and 24-27 cases per 100,000 children

Introduction: There is considerable interest in identifying potential etiologic and/or triggering agents for the severe immune response associated with Kawasaki disease (KD). The presence of environmental allergens might modulate the odds of triggering such a response despite those allergens not being direct etiologic agents. Methods: We queried the Canadian hospital discharge database (Canadian Institute for Health Information) for hospital admissions associated with a discharge diagnosis of KD in 2011 in the Greater Toronto Area. Atmospheric levels of pollens (35 species), spores (24 species) and fungi (27 species) were measured by Aerobiology Research Laboratories (Nepean, Ontario). A number of separate models were tested using theoretical incubation periods of 0, 7, 14 or 21 days. Correlation between KD cases and atmospheric levels of environmental allergens were assessed in linear regression models. Results: n=145 patients with KD were included. The highest levels of environmental allergens were in summer months. Overall atmospheric pollens levels were not associated with the KD cases (total pollen count r=0.04, p=0.54); there was no consistent pattern of association with specific pollens. . However, higher levels of spores were associated with a decreased prevalence of KD for all spore species (r=-0.23, pleptosphaeria, ascospores, oospore, coprinus/coprinellus, basidiospores, and uredinales . The same pattern was observed for all fungi species (r=-0.17, p=0.009). Associations were observed for 5 of 26 specific fungal species (p=0.002), including alternaria, cladosporium, epicoccum, fusarium, and fungi imperfecti . There were no discernable patterns regarding a potential incubation period. Conclusions: High levels of environmental allergens, particularly fungus and spores, were associated with lower incidence of KD. These results suggest that environmental allergens, even if they are not etiologic agents for KD, might modulate the threshold necessary for the actual etiologic/triggering agent. Atmospheric levels of environmental allergens might be partly responsible for the KD seasonality patterns observed in Canada.

Background: The etiology of Kawasaki disease (KD) is commonly described as an exaggerated immune response to an environmental or infectious trigger in developmentally, immunologically and genetically susceptible children. The trigger for KD has not yet been identified. Methods: Patients with newly diagnosed KD (n=73) were enrolled within 6 weeks of KD diagnosis. Control subjects (n=65) were enrolled during pediatric annual visits and from friends of enrolled KD patients. All participants completed an extensive questionnaire about medical history, family and environment. Geographic localisation software characterized the participants’ neighborhoods. A hypothetical scenario was used for control patients to simulate similar recall bias to that of the KD patients. Results: There were no differences in age, gender, allergies, child and family medical history or recent vaccination. Children with KD were more likely to be unwell prior to KD symptom onset than controls, including fever, stomach pain, lethargy, jaundice, loss of appetite and irritability, but not infectious disease symptoms (16% vs. 21%, p=0.49). Infectious symptomatology developed concurrently to classic KD symptoms. Children with KD had less exposure to environmental allergens and were more likely to be exposed to chemical irritants. Conclusions: The presence of symptoms for up to 1 month before onset of KD may suggest that a preceding illness/environmental agents may alter barriers to entry/exposure or prime an immunologic reaction to an etiologic trigger. Children with fewer allergen/infectious exposures and chronic chemical exposure may be immunologically more susceptible.

Introduction: Previous wind pattern studies have suggested that the etiologic and/or triggering agent for Kawasaki disease (KD) originates from Central Asia and that westward tropospheric winds are associated with the incidence pattern in Japan. This hypothesis has not been formally tested elsewhere. Should it be correct, it follows that incidence patterns should be similarly associated with North/North-West winds in Canada. Methods: We queried the Canadian hospital discharge database (Canadian Institute for Health Information) for hospital admissions associated with a discharge diagnosis of KD from 2004 through 2011; only acute admissions were included. Hourly weather data, including wind direction, was obtained from 9 weather stations across Canada situated closest to clusters of cases. The number of new KD admissions per day and per weather station was calculated. Wind direction was divided in 8 different quadrants covering 45° regions starting with 0°. A Poisson regression model for count data, adjusted for repeated measures (9 measures per day) was used to determine whether wind patterns were associated with incident cases. A number of separate models were tested using theoretical incubation periods of 0, 7, 14 or 21 days. Results: A total of 3363 KD cases were assigned to one of 26,283 time/space periods for which wind direction was available. Wind direction was not associated with incidence patterns in any of the 4 incubation models: incubation time 0 day (global wind pattern effect chi-square: 4.28, p=0.75). 7 days (chi-square: 5.08, p=0.65), 14 days (chi-square: 7.32, p=0.29) or 21 days (chi-square: 4.74, p=0.69). Focusing on North/North-West wind patterns also failed to show a significant association in all models: incubation time 0 day (+0.0021 (0.0151) cases/day, p=0.89), 7 days (-0.0071 (0.0142) cases/day, p=0.62), 14 days (+0.0009 (0.0148) cases/day, p=0.95) or 21 days (+0.0073 (0.0156) cases/day, p=0.64). Results were similar when stratifying Eastern vs. Western Canada and when each weather station was considered separately. Conclusions: Wind patterns were not found to be associated with incident KD cases in Canada. It is unclear if the reported association is specific to Japan or an ecologic fallacy.