Photo/IllutrationThe Asahi Shimbun

Two types of flu are spreading quickly throughout Japan in a growing and record outbreak, with an estimated 2.83 million people contracting the viruses last week, according to the Ministry of Health, Labor and Welfare.

The ministry announced Jan. 26 that the number of flu patients reported from monitor clinics and hospitals last week nearly doubled from the week before.

For the period of Jan. 15 to 21, the ministry revealed there were new 51.93 patients per medical institution on average. The figure almost doubled from the week before and surpassed the 30-patient mark, when the ministry usually sends out an official warning of an outbreak.

It is the largest number recorded since 1999 when the current survey method was rolled out.

About 5,000 medical institutions across Japan are designated as fixed-monitoring points for infectious diseases. They are required to report the numbers of patients of particular diseases to the authorities.

According the ministry, the nationwide estimate for flu patients in the week is about 2.83 million, as increase of 1.12 million from the week before.

By age group, about 590,000 flu patients aged between 5 and 9 formed the largest group. Youths aged 10 to 19 totaled 400,000.

By prefecture, Kagoshima Prefecture had the highest average number of patients per fixed-monitoring point clinics or hospitals with 86.53, followed by Miyazaki Prefecture, 84.97; Fukuoka Prefecture, 83.99; Oita Prefecture, 82.40; and Saga Prefecture, 69.64.

Tokyo reported 49.67, Aichi Prefecture, 62.12, and Osaka Prefecture, 44.17.

Of all 47 prefectures, the number has surpassed the warning mark of 30 in 44 prefectures.

The number of nursery schools, kindergartens, elementary and junior and senior high schools that were forced to close a class, a grade or the entire school to prevent the spread jumped to 7,536 institutions in the week from 161 the week before, a drastic rise by nearly 50 times.

There are primarily two types of viruses seen in the past five weeks. One is the Influenza A virus (H1N1), which was first reported and caused a pandemic in the 2009-2010 flu season, and another is the Influenza B virus. They are found almost evenly and together account for more than 80 percent of the infections.

Influenza B, which usually is more common in February and March, apparently started to become an epidemic earlier, and together with the A type, they are pushing up the number of flu patients.

“It seems the Influenza B virus is spreading mainly among children,” said Norio Sugaya from Keiyu Hospital in Yokohama. “We need to be vigilant as it could spread among adults and the elderly hereafter.”

This year, as Influenza A and B viruses are spreading at the same time, people could contract flu more than once in a season.

Sugaya said it is important to continue taking preventative measures even after recovering from the flu.

According to the flu expert, Influenza B causes a relatively lower fever than the A virus in adults. Grown-ups often mistakenly think they do not have flu, then go out and end up infecting more people with the virus.

“When you have suspected symptoms, even just a minor fever, please see a doctor to take the test (for influenza viruses),” said Sugaya.

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