The number of influenza patients per medical institution in Japan exceeded the alarm level of 30, which suggests an outbreak of the disease, in the week through Sunday, the health ministry has said.
The number grew by 22.24 from the preceding week to 38.54, according to a survey that covered reports from about 5,000 regularly monitored medical institutions.
The total number of flu patients who were treated at medical institutions across the country during the week is estimated at some 1,635,000, nearly tripling from some 586,000 the previous week.
By prefecture, the number of patients per institution was highest in Aichi, at 75.38, followed by Kumamoto, at 58.79, Gifu, at 53.94, Kagoshima, at 52.34, and Shizuoka, at 52.22.
Of the flu viruses detected in patients in the past five weeks, type A, which spread globally as a new type in 2009, accounted for the biggest share, followed by the type-A Hong Kong strain and type B.