An expert of infectious diseases indicates that Japan's influenza outbreak may peak in the next few weeks.

The National Institute of Infectious Diseases says about 5,000 medical institutions nationwide reported a total of more than 51,000 influenza cases during the seven-day period through Sunday.

The number of flu patients per institution during the week was 10.36. A figure above the advisory level of 10 indicates that a major spread of the virus is possible in the coming four weeks.

The southern prefecture of Okinawa reported over 41 patients per institution during the seven-day period.
Okinawa's figure has exceeded 30 -- the threshold to issue a warning -- for three straight weeks. The prefecture issued the warning on January 19.

There were 16 prefectures that had an outbreak exceeding the advisory level. They include Fukui with 25, Osaka with 24, Fukuoka with 21 and Kyoto with 20.

Toho University Professor Tateda Kazuhiro says that the spread of the flu virus has slightly slowed, but that infections usually peak in February.

Tateda calls on people to stay alert and take measures, such as the appropriate use of face masks, in the coming few weeks.