TOKYO, Jan. 21 (Xinhua) -- The average number of flu patients per medical institution in Japan in the week through Sunday came to 7.37, signaling the beginning of an epidemic, a health ministry survey said.

People shop at a supermarket in Tokyo on January 20, 2023. (File photo: AFP)

The nationwide per-institution figure was more than 1.5 times that of the previous week, while the tally of influenza patients across the country is estimated to stand at about 257,000.

By prefecture, the per-hospital number was the highest in Okinawa at 33.23. The number was above 10 in seven other prefectures, including Fukuoka at 16.96, Miyazaki at 16.63 and Saga at 15.79.

A reading above 10 suggests a major spread of seasonal flu could occur within four weeks, while a reading above 30 signals that a major spread is suspected to have occurred.