In February 2006, a new vaccine against rotavirus, RotaTeq, was licensed by the US Food and Drug Administration, and currently the Advisory Committee on Immunization Practices recommends routine immunization of all US children against rotavirus, starting at 6 weeks of age . In June 2007, the FDA revised the package label for RotaTeq to include information on cases of Kawasaki syndrome (KS), due to rare reported cases in pre-licensure studies . Based on a review of pre-licensure and available post-licensure surveillance data, the FDA concluded that there is not a known cause and effect relationship between receiving RotaTeq and the occurrence of KS.
KS is an uncommon childhood illness that is characterized by high fever and inflammation of the blood vessels throughout the body. Approximately 4,000 children each year in the United States develop KS, about eighty percent of whom are younger than 5 years of age [3, 4]. The cause of KS is unknown ; it has been hypothesized that an infectious agent is involved in the etiology of KS  but no specific association has been confirmed. In a single study from Japan, where a higher incidence of KS than in the United States has been noted, rotavirus particles or capsomers were identified in 74% of 39 KS cases versus 11% of 18 controls and a rise in serum antibody to rotavirus was identified in 51% of 75 KS cases versus 8% of 39 controls . While these data raised the possibility of an association between rotavirus infection and KS, no studies to confirm these findings have been reported.
Because the etiology of KS remains unknown, and the possibility of an association between KS and rotavirus infection has been raised , we sought to further examine the relationship between these diseases. Furthermore, a better understanding of any potential association between KS and natural rotavirus infection could help assess the biologic plausibility of a relationship between rotavirus vaccination and KS. Therefore, we examined the seasonal patterns of hospitalizations associated with rotavirus gastroenteritis and with KS for the US states of California and New York, to evaluate whether the two diseases temporally coincided.