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Fig. 2 | BMC Infectious Diseases

Fig. 2

From: A maximum curvature method for estimating epidemic onset of seasonal influenza in Japan

Fig. 2

Illustration of the maximum curvature method (MCM). Panel a demonstrates the epidemic curve of weekly number of ILI cases per sentinel for Okinawa during 2012/2013. The red dashed horizontal line indicates the upper threshold of h=5.0 ILI cases per sentinel per week. Panel b shows the raw curvature of the fitted least-squares circle in each week. Panel c shows the directional angle θ of the tangent vector \( \overrightarrow{PQ} \) in each week. The red dashed horizontal lines indicate 90°, 180°, and 270°. The gray shaded areas respectively represent [0°, 90°] during the first half of the epidemic curve, and [270°, 360°] during the second half, within which θ would be expected to lie. Panel d shows the curvature filtered by h and θ in each week. The blue solid points represent the maximum filtered curvatures in the first and second halves of the epidemic curve. The corresponding blue dashed vertical lines across the panels indicate the epidemic onset and ending weeks

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