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For the second time in a week, illness has cut short another cruise line vacation, this time on the Caribbean Princess.

The ship, operated by Princess Cruises, is heading back to Houston on Friday, a day early because of an outbreak of suspected norovirus, according to An outbreak of gastrointestinal illness has sickened at least 173 people on board, according to the Centers for Disease Control and Prevention.

That includes 162 of the 3,102 passengers and 11 of the 1,148 crew members, the CDC reported. Two CDC health officials were expected to board the ship on Friday. The vessel launched on a seven-day cruise to the western Caribbean on Jan. 25. It was scheduled to return on Saturday.

Princess Cruise line officials did not immediately return calls to NBC News.

The move follows a high-profile outbreak of illness on the Royal Caribbean ship Explorer of the Seas, which returned early to New Jersey on Wednesday after a fast-moving stomach bug sickened nearly 700 people.

This is the third cruise ship outbreak to occur this year alone. A Norwegian Cruise Line ship, the Norwegian Star, reported that 130 passengers and 12 crew members fell ill on two-week cruise that launched Jan. 5 from Miami.

About 20 million passengers take cruises in the U.S. each year, fueling a $37.8 billion annual industry, according to the American Association of Port Authorities. There were nine vessel outbreaks in 2013 and 16 in 2012, according to the CDC.

Cruise ships that carry 13 or more passengers and have a foreign itinerary with U.S. ports are under the jurisdiction of the CDC’s Vessel Sanitation Program and cruise lines pay voluntary fees for inspection and training services. They’re required to tell CDC if 2 percent or more of passengers on a ship fall ill, the CDC says.

Norovirus is a common culprit in outbreaks on cruise ships, in nursing homes and other confined places. It is a fast-moving gut bug typically spread by infected people or contaminated food or water. Norovirus is the most common cause of acute gastroenteritis in the U.S., resulting in about 21 million illnesses, between 56,000 and 71,000 hospitalizations and as many as 800 deaths, the CDC says.

The virus lingers on surfaces and spreads very easily. Thorough handwashing with hot water and soap and meticulous environmental cleaning can help stop the spread.