Association of Kawasaki disease with tropospheric wind patterns

Abstract

The causal agent of Kawasaki disease (KD) remains unknown after more than 40 years of intensive research. The number of cases continues to rise in many parts of the world and KD is the most common cause of acquired heart disease in childhood in developed countries. Analyses of the three major KD epidemics in Japan, major non-epidemic interannual fluctuations of KD cases in Japan and San Diego, and the seasonal variation of KD in Japan, Hawaii, and San Diego, reveals a consistent pattern wherein KD cases are often linked to large-scale wind currents originating in central Asia and traversing the north Pacific. Results suggest that the environmental trigger for KD could be wind-borne. Efforts to isolate the causative agent of KD should focus on the microbiology of aerosols.

Figure 1. Major epidemics of monthly KD incidence in Japan.

The three main historical KD epidemics are highlighted in red in panel a (cases). Time averaged sea level pressure (hPa) and surface winds (m/s) prior to the March/May 1979, May 1982 and March 1986 epidemics are shown in panels b, c and d, respectively. Monthly atmospheric variables were averaged for the preceding summer (JJA 1978 in b1, JJA 1981 in c1, and JJA 1985 in d1), when winds from the south typically blow across Japan, and for the rising phase of the epidemics, from September to the last month before the peak (Sep 1978 to Mar 1979 in b2, Sep 1981 to Apr 1982 in c2, and Sep 1985 to Feb 1986 in d2) , when winds shifted and blew from the northwest. Colored dots depict the increase in KD incidence (per million inhabitants) by prefecture between the preceding September and the peak (Apr 1979 minus Sep 1978 in b2, May 1982 minus Sep 1981 in c2, and Mar 1986 minus Sep 1985 in d2).

Figure 2. Surface configuration for the major interannual peaks of KD incidence in Japan.

Panel a depicts the standardized (unitless) interannual reconstructed component of the original monthly time series of KD shown in Supplementary Figures 1a. The 7 (5) interannual peaks (troughs) reaching the +1 (−1) standard deviation criterion are dashed in red (blue). Standardized (unitless) interannual anomalies of sea level pressure and surface winds were composited in panel b (c) for the set of months when these peaks (troughs) were observed. Thick contours depict regions with significant interannual sea level pressure anomalies (p <0.05).

Figure 3. Upper-troposphere wind configuration for the major interannual peaks of KD incidence in San Diego.

Panel a depicts the standardized (unitless) interannual reconstructed component of the original monthly time series of KD shown in Supplementary Figures 1c. Standardized (unitless) interannual anomalies (b,c) and actual observations (d,e) of 300 hPa wind direction and intensity were composited for the 4 green (b,d) and 3 orange (c,e) interannual peaks in panel a. Thick contours in panels b and c depict regions with significant interannual wind intensity anomalies (p < 0.05).

Figure 4. KD and surface winds in Japan (a), San Diego (b) and Hawaii (c).

Time series correspond to KD incidence (red lines in a, b and c), the northwestern component of surface winds in Japan (NW-WIND, blue line in a; m/s), and the Pacific Zonal Wind Index (P-WIND, blue lines in b and c; m/s). NW-WIND is defined as the projection of the horizontal two-dimensional wind onto a unit vector in the northwest/southeast direction (i.e. cos(45°)·uwind −sin(45°)·vwind). P-WIND is defined as the mean zonal wind along 35°N between longitudes 140°E and 240°E (see the horizontal green line in Figures 5a,b). P-WIND is shown here for the surface level, but similar results were found for the middle and upper troposphere (e.g. Figure 5d). KD time series for San Diego and Hawaii are reconstructed components obtained after applying an eigendecomposition analysis to the KD data, to better isolate the annual component (see Methods). KD cases in Hawaii were accumulated prior to the eigendecomposition.

Figure 5. Tropospheric winds in the North Pacific.

Climatological January values are depicted for sea level pressure (hPa, a), surface winds (m/s, a), geopotential height at 300 hPa (m, b), and winds at 300 hPa (m/s, b). Panels c and d depict the seasonal cycle of the northwestern component of tropospheric winds in Japan (NW-WIND, m/s) and of the Pacific Zonal Wind Index (P-WIND, m/s), respectively. NW-WIND is here defined as the projection of the horizontal two-dimensional wind onto a unit vector in the northwest/southeast direction (i.e. cos(45°)·u_wind −sin(45°)·v_wind). P-WIND is defined as the mean zonal wind along the parallel 35°N between longitudes 140°E and 240°E (see the horizontal green line in panels a and b).