One hundred and thirty-nine people on the Cunard Queen Victoria cruise ship have reported gastrointestinal symptoms like vomiting and diarrhea with a mystery illness ravaging the vessel. The ship is in its third week of fifteen in a journey around the world. The outbreak has been monitored by the Centers for Disease Control and Prevention since Jan. 22 when the ship docked at Fort Lauderdale, although the cause and exact nature of the disease is unclear. Cruise ships are notorious breeding grounds for norovirus, which has earned it the nickname “cruise ship virus,” because the gastrointestinal disease’s quick person-to-person spread is facilitated by the densely populated close quarters and shared spaces on cruise ships. A Cunard spokesperson told NBC News that after initial reports they “immediately activated their enhanced health and safety protocols,” which included quarantining the ill and beefing up sanitation measures. It is next set to arrive in San Francisco on Feb. 6.