Seven foodborne norovirus outbreaks attributable to the GII.P17-GII.17 strain were reported across Japan in 2017, causing illness in a total of 2,094 persons. Nori (dried shredded seaweed) was implicated in all outbreaks and tested positive for norovirus. Our data highlight the stability of norovirus in dehydrated food products.

Foodborne outbreaks caused by human norovirus GII.P17-GII.17-contaminated Nori, Japan, 2017

Emerging Infections Diseases, Volume 24, Issue 5, May 2018,  https://doi.org/10.3201/eid2405.171733

Naomi Sakon, Kenji Sadamasu, Takayuki Shinkai, Yousuke Hamajima, Hideaki Yoshitomi, Yuki Matsushima, Rika Takada, Fumio Terasoma, Asako Nakamura, Jun Komano, Koo Nagasawa, Hideaki Shimizu, Kazuhiko Katayama, and Hirokazu Kimura

https://wwwnc.cdc.gov/eid/article/24/5/17-1733_article