(11:30 a.m.) -- Carnival Liberty is on its 16-day voyage to Ft. Lauderdale from Rome with a few unwanted passengers ... germs, that is. As of end of day yesterday, 556 out of 2,804 guests and 154 out of 1,166 crewmembers had reported symptoms of Norovirus, an extremely common and highly contagious virus that causes gastroenteritis, often called "stomach flu."

The bad news is these figures are pretty significant, accounting for 27 percent of all passengers and 13 percent of all staffers, or 18 percent shipwide. The good news? The number of new cases being reported is dropping, according to a statement from the cruise line, and the majority of affected guests have already recovered.

After departing on November 3, at least two guests fessed up to being sick with gastrointestinal illness prior to the cruise and had even sought medical treatment in Rome before boarding Carnival Liberty, according to the statement. Though Norovirus can be passed via contaminated food and water, it is typically spread through people-to-people contact -- i.e. guests who set sail sick and pass it around.

Five days into the voyage, member beachbrat posted from the ship that "our cruise director is keeping everyone updated. He is emphasizing how important it is to keep hands clean, etc." In addition to promoting good hygiene, the cruise line has ramped up Liberty's own cleaning procedures in response to the outbreak; disinfection with special (stronger) cleansing agents is ongoing. The buffet was switched from self-service to being manned by crew to prevent guests from touching utensils.

The ship is scheduled to end its cruise on November 19. At this point, the cruise line has not announced any Noro-related changes to this or future itineraries; we'll keep you posted.

Norovirus: What You Need to Know

--by Melissa Baldwin, Senior Editor