The incidence of Kawasaki syndrome in West Coast health maintenance organizations.

Background. Kawasaki syndrome (KS) causes an acute vasculitis of unknown etiology. It is a leading cause of acquired heart disease of children in Japan and the United States. Methods. We examined the incidence of KS in a well-defined population group of children ≤6 years of age, using data collected through the Vaccine Safety Datalink (VSD) project. The VSD database contains information on >1 million children enrolled in four West Coast health maintenance organizations (HMOs). Results. During 1993 through 1996 a total of 234 physician-diagnosed KS patients were reported in the 4 HMOs; 152 (65.0%) were boys and 195 (83.3%) were <5 years of age. The incidence of KS among children <5 years of age in the HMOs ranged from 9.0 to 19.1 per 100 000 person years. KS incidence was higher among boys in 3 of the sites. In the 2 sites with the highest number of KS patients, a seasonal occurrence of KS in winter and early spring was observed. Overall 226 (96.6%) of the KS patients were reported to have been hospitalized; hospitalization rates for children <5 years of age ranged from 9.0 to 16.8 per 100 000 person years. Conclusions. The incidence of KS in the HMOs was similar to that reported in other population-based studies in the United States and higher than estimates for Australia and several European countries.