Spatiotemporal clusters of Kawasaki disease in South Korea from 2008 to 2017: A municipal-level ecological study

Introduction As the etiology of Kawasaki disease (KD) remains unknown, identifying spatiotemporal clusters with proper stratification of KD could provide further evidence for investigating the triggers of KD. However, spatiotemporal distributions of KD with sex stratification have never been reported. Therefore, we aimed to analyze the spatiotemporal patterns of KD by sex in South Korea. Methods We extracted epidemiologic week (Epiweek)-based KD cases in patients <5 years of age (ICD-10-CM code: M303) from 2008 to 2017 national health insurance service data at the 250 municipal level. To determine whether spatial autocorrelation and persistent municipal-level clusters exist, year- and sex-stratified global Moran's I statistics, Getis-Ord Gi* statistics, and emerging hotspot analysis on KD incidence were conducted. Results A total of 72,510 KD cases were reported between 2008 and 2017 (male-to-female ratio = 1.40:1). Incidence has increased since 2008, with the highest incidence in 2016 (396.8 per 100,000 population). KD had seasonality of winter and summer but different by sex. Positive spatial autocorrelation was consistently reported in every stratum, with the 2011–2014 period having the strongest index value (total sex I = 0.286, p < 0.001; male I = 0.242, p < 0.001; female I = 0.213, p < 0.001). Hot spots were consistently detected in the northern parts, and cold spots were in the southern part for 9 years in both sexes. The emerging hot spot analysis showed new, consecutive, and sporadic hot spots on the northwestern and eastern coasts and new and sporadic cold spots in the southwestern part. However, the distribution and proportion of hot or cold spot types differed according to sex. Discussion The spatiotemporal features of KD had limits to concluding that only infectious triggers result in KD occurrence. Therefore, our findings support the notion that KD is a syndrome with multiple factors, including infectious, genetic, and environmental factors, that are associated with sex differences.

A location has a statistically significant hot spot in the final time step and has never been a statistically significant hot spot before the final time step

Consecutive Hot Spot
A location has a single uninterrupted run of at least two statistically significant hot spot bins in the final time-step intervals and has never been a statistically significant hot spot before the final hot spot run, and less than 90% of all bins are statistically significant hot spots Intensifying Hot Spot A location has been a statistically significant hot spot for 90% of the time-step intervals, including the final time step, and the intensity of clustering in each time step is statistically significantly increasing overall Persistent Hot Spot A location has been a statistically significant hot spot for 90% of the time-step intervals without an identifiable increasing or decreasing trend in the intensity of clustering over time Diminishing Hot Spot A location has a statistically significant hot spot for 90% of the timestep intervals, including the final time step, but the intensity of clustering in each step is statistically significantly decreasing overall

Sporadic Hot Spot
A location with an on-again, off-again hot spot, with less than 90% of the time-step intervals being statistically significant hot spots and never having the time-step intervals of statistically significant cold spots

Oscillating Hot Spot
A location is a statistically significant hot spot for the final time-step interval, but has a statistically significant cold spot during a prior time step and has less than 90% of the time-step intervals being statistically significant hot spots

Historical Hot Spot
A location is not a hot spot in the most recent time period, but at least 90% of the time-step intervals have been statistically significant hot spots New Cold Spot A location has a statistically significant cold spot in the final time step and has never been a statistically significant cold spot before the final time step

Consecutive Cold Spot
A location has a single uninterrupted run of at least two statistically significant cold spot bins in the final time-step intervals and has never been a statistically significant cold spot before the final cold spot run, and less than 90% of all bins are statistically significant cold spots

Intensifying Cold Spot
A location has been a statistically significant cold spot for 90% of the time-step intervals, including the final time step, and the intensity of clustering in each time step is statistically significantly increasing overall

Persistent Cold Spot
A location has been a statistically significant cold spot for 90% of the time-step intervals without an identifiable increasing or decreasing trend in the intensity of clustering over time

Diminishing Cold Spot
A location has a statistically significant cold spot for 90% of the timestep intervals, including the final time step, but the intensity of clustering in each step is statistically significantly decreasing overall

Sporadic Cold Spot
A location with an on-again, off-again cold spot, with less than 90% of the time-step intervals being statistically significant cold spots, and never having the time-step intervals of statistically significant hot spots

Oscillating Cold Spot
A location is a statistically significant cold spot for the final time-step interval, but has a statistically significant hot spot during a prior time step, with less than 90% of the time-step intervals being statistically significant cold spots