Photo/Illutration This undated handout image shows influenza viruses. (Provided by the Japan Institute for Health Security)

The influenza outbreak has triggered a national alert as flu cases are surging and hospitalizations are increasing, particularly among children and the elderly, the health ministry announced on Nov. 21.

The national alert comes five weeks earlier than last season.

The average number of patients per designated medical institution jumped to 37.73 in the week of Nov. 10-16, a 1.7-fold increase from the previous week’s 21.82, the health ministry reported.

The alert level is triggered when the average exceeds 30 patients per designated medical institution.

The threshold was surpassed in 24 of Japan's 47 prefectures. The outbreak is particularly severe in eastern Japan, with Miyagi Prefecture reporting the highest figure at 80.02 cases per institution, followed by Saitama Prefecture with 70.01.

Major metropolitan areas were also hit hard, with Tokyo at 44.75 and Osaka at 31.57.

Hospitalizations for the week totaled 1,466, an increase of more than 500 from the previous week. The most affected age groups were children aged 1-4 and 5-9, and adults 80 and over.

The spike has also led to a sharp rise in school and class closures. A total of 6,235 educational and child care facilities nationwide suspended operations, nearly 1.7 times the number from the previous week.

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