Biomedical illustration of noroviruses in the gastrointestinal tract. Noroviruses, family Caliciviridae, are a group of single-stranded RNA, non-enveloped viruses that cause acute gastroenteritis in humans. Noroviruses spread from person to person, through contaminated food or water, and by touching contaminated surfaces. Norovirus is the leading cause of non-bacterial food-borne disease outbreaks in the United States. Also shown are cross-sections of villi and epithelial cells.outbreaks in the United States. Also shown are cross-sections of villa and epithelial cells. .