Japanese health authorities say the high number of influenza cases across the country for the seven days through Sunday remained at the same level as the previous week.

The National Institute of Infectious Diseases and other facilities say about 5,000 medical institutions nationwide reported a total of 35,021 flu cases during the week.

The number of flu patients per institution stood at 7.09. Based on the data, health officials estimate there were about 258,000 cases of flu infection.

By prefecture, the southern prefecture of Okinawa reported more than 22 patients per institution, followed by Chiba at over 15 and Ehime at a little over 14.

A total of nine prefectures reported cases over the advisory level of 10 patients per institution for the same period. The six others are Miyazaki, Oita, Tokyo, Ibaraki, Yamaguchi and Saitama.

A figure above the advisory level is believed to indicate a major flu outbreak may strike in the coming four weeks.