Kawasaki disease: Epidemiological differences between past and recent periods, and implications of distribution dynamism

BACKGROUND: Epidemiological findings suggest that Kawasaki disease (KD) is mediated by infection, which triggers its onset. Although the mechanism of onset seems to involve preconditioning factors and triggering factors, the details remain unclarified. METHODS: Data for 330 662 patients reported in KD nationwide surveys in Japan implemented between 1961 and 2014 were chronologically compared in terms of patient age distribution, estimated mean onset age, and male-to-female ratio during four periods: pre-epidemic (P1), epidemic (P2), stable (P3), and recent (P4): 1961-1978, 1979-1986, 1987-1997, and 1998-2014, respectively. RESULTS: During P2, the number of patients aged 6 months-2 years increased, and the mean onset age was younger; during P4, however, the number of patients aged ≤1 year decreased, but the number of patients ≥2 years increased, with a flat onset age distribution chart, and the mean onset age was older. During P2, increases in the number of patients were accompanied by younger mean onset age, whereas during P4, increases in the number of patients were conversely accompanied by older mean onset ages. The male: female ratio tended to decrease during P2, but this tendency was not seen in P4. No outbreak occurred during a recent 28 year period (P3, P4). Specific preconditioning factors might have been present during the 8 years (P2) of the past three outbreaks. CONCLUSION: P2 and P4 were significantly different in epidemiological features. It is likely that they do not share the same mechanism of onset (preconditioning and/or trigger factors).