July 18 (UPI) -- The U.S. Centers for Disease Control and Prevention has announced that an unknown illness sickened more than 100 people aboard a Royal Caribbean cruise ship earlier this month. According to a press release from the CDC's Vessel Sanitation Program, a "gastrointestinal illness outbreak" occurred on the Navigator of the Seas that traveled round-trip to Mexico from Los Angeles between July 4 and11. Out of the 3,914 passengers , 134 reported being ill, as did seven crew members. The