Norovirus outbreaks at nursing homes in osaka, Japan.

*Corresponding author: Mailing address: Department of Infectious Diseases, Osaka Prefectural Institute of Public Health, 13-69 Nakamichi, Higashinari-ku, Osaka 537-0025, Japan. Tel: +81-6-6972-1321, Fax: +81-6-6972-2393, E-mail: nsakon@ iph.pref.osaka.jp An epidemic outbreak of norovirus (NoV) raged through nursing homes in Japan in the past winter season (January, 2005). Twenty-five outbreaks of confirmed NoV in nursing homes and hospitals were involved, together with 13 outbreaks in other facilities. In the present report, we describe three separate outbreaks that occurred in nursing homes in Osaka, Japan. Case 1 Between the 15th and 16th of December 2004, two residents in a nursing home in Daito City showed symptoms of gastroenteritis including vomiting and fever, and were diagnosed with viral gastroenteritis in a hospital; five other residents had similar symptoms. NoV infection was suspected to have been spread by person-to-person contact and was not considered to be foodborne because there was no common source of food. On the 22nd of December, four stool samples were tested. NoV (GII.4; CAW type) was detected in all samples by reverse transcriptase-polymerase chain reaction (RT-PCR) using G2F1/G2SKR primers and Yuri primers (1,2). In total, 39 residents had symptoms; 2 of 28 residents on the second floor, 16 of 35 residents on the third floor, 14 of 35 residents on the fourth floor, and one short-term resident on the first floor. Additionally, 6 staff members, including one cook had symptoms of gastroenteritis (Fig. 1A). Most of those infected were located on the third and fourth floors. Residents of the third floor had senile dementia, residents of