Patterns of Migration Underlie the Increasing Incidence of Kawasaki Disease in Sweden from 1987 to 2018: a Cohort Study.

OBJECTIVE:To define the demographics of Kawasaki disease (KD) in Sweden during a 32 year period. METHOD:Routinely collected administrative and healthcare data from nationwide Swedish registers were collected for this population-based cohort study. The case definition was individuals under the age of 25 and diagnosed with KD from 1987 to 2018. Main measures included incidence rate, year and month of diagnosis, sex and age at diagnosis, patient's and parents' world region of birth, and home county. RESULTS:In total, 1917 cases were identified. Median age at diagnosis was 2.82 years (interquartile range 1.47-5.13) and 62% were males. Relative incidence rates in winter [1.29, 95% confidence interval (CI) 1.14-1.47] and spring (1.21, 95% CI 1.07-1.38) were higher than in the reference season (summer), while incidence over the study period varied geographically across counties, with no discernible pattern. The incidence rate in the population increased during the 32 year period from 3.6 to 12.1 (95% CI 9.1-15.2) per 100 000 under-5-year-olds during the last 5 years of the study. This increase related mainly to cases with one or two parents of non-Swedish, predominantly Asian and African, origin. Two significant peaks in incidence rates in 2008 and 2015 were also observed, mainly relating to cases with two Swedish-born parents. CONCLUSION:Our study confirms the age and sex distribution as well as seasonal variation and occurrence of peak years of KD. Migration patterns were associated with increasing numbers of KD, which is important to consider for healthcare planning and for defining risk groups.