With the influenza season approaching its peak this winter, the number of patients reached about 660,000 nationwide in the week of Jan. 13 to 19, almost doubling the 340,000 tallied the previous week.
The Health, Labor and Welfare Ministry issued a warning last week that the outbreak has reached epidemic proportions and that the peak won't be reached until early February.
The health ministry said Okinawa Prefecture, followed by Miyazaki, Gifu, Oita and Fukuoka, are the hardest-hit areas.
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