Multiple outbreaks of gastroenteritis due to a single strain of genotype GII/4 norovirus in Kobe, Japan, 2006: risk factors for norovirus spread in health care settings.

A large number of gastroenteritis outbreaks due to a norovirus GII/4 strain and its variants occurred during November and December 2006 in Kobe, Japan. Of the 118 outbreaks, 6 were foodborne and 112 were caused by person-to-person transmission in healthcare settings such as nursing homes and hospitals. The distribution of norovirus outbreaks in healthcare settings was skewed, particularly in the south coastal area. Moreover, several outbreaks occurred within 1 km(2) in various areas. Outbreaks in neighboring settings, especially within 1 km, and travel from the sources of outbreaks were risk factors for the spread of the norovirus. The use of ineffective disinfectants such as alcohol and benzalkonium chloride might also have helped to spread the infection.