More than 200 passengers aboard Carnival Cruise Lines' Conquest fell ill last week due to a gastrointestinal disorder that has plagued the cruise industry over the last three months. Physicians say the Norwalk-like virus is believed to be the same that has sickened hundreds of passengers aboard at least three cruise ships since September. The Conquest left New Orleans on December 8 with 3,160 passengers and returned Sunday. Carnival officials believe a passenger who reported being sick two days before the ship left port most likely carried the virus onto the vessel.