The health ministry has urged local governments to pay attention to a norovirus epidemic after suspected cases of infectious gastroenteritis caused by norovirus this year increased at the highest pace since 2006.

The average number of suspected norovirus patients reported by 3,000 medical institutions stood at 11.39 in the week of Nov. 12-18, the highest number seen in the period since 16.42 in 2006 and close to last year's peak of 12.76, the National Institute of Infectious Diseases said Tuesday.

The number came to as high as 22.42 in Miyazaki Prefecture, 20.03 in Fukuoka Prefecture, 19.42 in Oita Prefecture, 19.21 in Osaka Prefecture and 18.36 in Hyogo Prefecture.

Gastroenteritis symptoms caused by norovirus include repeated vomiting and diarrhea, and end in a day or two. But norovirus could also cause dehydration in young children and the elderly, affecting chronic diseases.

Humans can be infected if they eat oysters containing norovirus or inhale near dry vomit from infected patients. Some of those infected may not develop any related symptoms, however.