Public health officials in Japan say the average weekly number of influenza patients per medical institution has hit a record high.

The National Institute of Infectious Diseases carries out a survey of about 5,000 medical institutions. It says a total of 317,812 cases were reported in the week to December 29, an increase of over 100,000 from the previous week.

The average number of 64.39 flu cases per medical institution is the highest since the survey started in its current form in 1999. The figure increased by 21.73 from a week earlier.

By prefecture, Oita in southwestern Japan topped the list with 104.84 cases. Kagoshima, also in the southwest, had 96.4 cases. Osaka had 67.53 cases, while Tokyo had 56.52.

The weekly number increased in all 47 prefectures compared to the previous week. In 43 of them, the weekly number of patients per medical institution exceeded the warning level of 30 cases.

The rapid increase in the number of flu patients has created a shortage of anti-influenza drugs.

An Osaka-based generic drug manufacturer, Sawai Pharmaceutical Company, says it has temporarily suspended shipments of its anti-flu drug in both capsule and syrup formats.

The firm says it is unable to keep up with the sharp increase in demand since mid-December. It suspended shipments to medical institutions on Wednesday.

The maker says it continued operating its plants during the yearend and New Year holidays. It plans to resume shipments of the syrup in late January, and capsules in early February.

According to health ministry data for last November, the drug accounted for around 25 percent of the total supply of anti-influenza drugs made available to medical institutions.

The ministry is asking clinics, hospitals, and pharmacies not to order more than they actually need, and to consider using similar drugs produced by other pharmaceutical companies.