Kawasaki syndrome in Denmark.

Fischer, Thea K; Holman, Robert C; Yorita, Krista L; Belay, Ermias D; Melbye, Mads; Koch, Anders

OBJECTIVE To describe the epidemiologic characteristics of Kawasaki syndrome (KS) and to estimate national KS incidence rates among children in Denmark. METHODS A retrospective population-based study using hospital discharge records with a KS diagnosis for children younger than 15 years selected from the Danish National Hospital Register for 1981-2004. Incidence rates were calculated using the number of KS patients and corresponding census data. RESULTS During 1981-2004, 360 children younger than 15 years were hospitalized with KS in Denmark, with 73% younger than 5 years. In this age group, the average annual incidence of KS gradually increased from 1981 to 1999 and thereafter stabilized at 4.5 to 5.0 per 100,000 person-years. The incidence was greater for boys than for girls (RR = 1.6, 95% CI = 1.2-2.0) and was highest among infants younger than 1 year (4.5), declining with increasing age (P = 0.03). However, the age-specific decline in incidence was only observed for boys, whereas the incidence for girls remained unchanged by age. The median length of hospital stay was 12 days, and the incidence peaked in the winter months. CONCLUSIONS Major epidemiologic characteristics identified among Danish childhood KS are consistent with those described in previous studies, such as highest incidence among young children and winter-seasonality. The KS incidence rate among children younger than 5 years in Denmark increased steadily during the early study period (coinciding with global recognition of KS) and seems to have stabilized from 1998-1999 onwards. Although the incidence among Danish children was lower than that reported for several other European countries, differences in methodology challenge definite comparisons.