In 2011 an outbreak of diarrhea and vomiting occurred among people who participated in the Rock 'N' Roll Marathon in Las Vegas, Nevada. No source of the outbreak was discovered, but based on the incubation period and time of illness onset, it is likely that exposure occurred prior to the onset of the race, most likely at the health and fitness expo. Media reports and participant comments tended to focus on the water provided to runners during the race as the purported source of illness. Outbreaks of sapovirus have been reported in the literature, but reports of foodborne outbreaks and outbreaks among adults outside long-term care are rare. The investigation was conducted using social media.