Photo/IllutrationThe Asahi Shimbun

The influenza epidemic has reached new heights for the third straight week, the health ministry said Feb. 9, with an absence of high fever making many sufferers unaware they are carrying the virus.

The average number of patients infected hit a new high of 54.33 per medical institution during the latest count for the week through Feb. 4, with a majority of the patients infected with the type B variant of the flu.

Medical experts fear that some type B flu sufferers are spreading the virus at workplaces and schools unknowingly as they do not regard their symptoms as the flu.

The latest figure was calculated by the number of flu sufferers reported at about 5,000 medical institutions that are designated as fixed monitoring points across the country between Jan. 29 and Feb. 4. The number for the preceding week was 52.35.

An estimated 2.82 million people are inflicted with the illness nationwide, up from 2.74 million during the week through Jan. 28.

By prefecture, Oita had the highest rate at 77.09, followed by Fukuoka at 69.96, Saitama at 68.29, Kanagawa at 66.31 and Kochi at 66.19, according to the health ministry.

The number for Tokyo was 53.23, Aichi 62.52 and Osaka 45.02.

All 47 of the nation’s prefectures far exceeded the “alert level” of 30, the ministry said.

By age group, those aged 5-9 represented the most, with an estimated 620,000 cases.

The type B virus was responsible for 51.8 percent of flu sufferers who were treated at medical institutions over the five weeks through Feb. 4, and the number of patients hit by the type is increasing week after week.

Type B usually strikes in February and March, but it began spreading earlier this year than usual.

Over the same period, type A Hong Kong flu was responsible for 26.2 percent of the infections, while Influenza A virus (H1N1), which caused an outbreak in the 2009-2010 season, was blamed for 22 percent of the cases.

Medical experts warned that a person can be infected with more than one type of flu this season due to the three types of viruses spreading at the same time.

(This article was written by Shuichi Doi and Keitaro Fukuchi.)