On Sunday, the Crown Princess docked in California after 172 people became sick from the highly contagious norovirus.

More than four percent of the ship, which had a total of 4,167 people on board including 3,007 passengers, got sick during a nearly 28-day voyage from Los Angeles to Hawaii to Tahiti.

The ship underwent a deep cleaning at a terminal in San Pedro before it left last night on its next voyage to the Mexican Riviera.  The Centers for Disease Control and Prevention is scheduled to board the ship to investigate the outbreak and see how the cruise line will handle future health and safety procedures.

Princess Cruises spokeswoman Susan Lomax told FoxNews.com that for the embarking passengers on the new voyage who were delayed by the cleaning, the cruise line refunded a day-and-a-half of their cruise fare and provided onboard and future cruise credits.  Passengers on the cruise that were on the voyage affected by the norovirus will not receive any compensation. 

“All ports of call were visited as planned.  In fact, we are getting praise from our passengers onboard for our swift action to stop the spread and the great communication from the Captain!,” she wrote in an email.

The Cruise Ship Disease?

Norovirus is a disease that is not limited to cruise lines. In fact, it strikes anywhere there is a large concentration of people.  Approximately 20 million people catch the norovirus each year from contact with infected people or by eating contaminated food, according to the CDC. The illness, which includes symptoms such as vomiting, diarrhea, fever and body aches, is often wrongly identified as “stomach flu” or “food poisoning.” According to the CDC norovirus website, the disease is highly contagious and only takes 10 to 100 viral particles to catch it, whereas the common flu requires about 10,000 particles.  As the second most common virus in the nation, norovirus can break out any place, and it commonly does.

Avoiding Norovirus on Cruise Ships 

The virus can also live on surfaces for many hours, even days. The best way to avoid the disease is simple --basic hygiene. 

That was a message Lomax reiterated: “As it is the cold and flu season, when the stomach flu circulates on land, we encourage all of our guests to be diligent in following the widely accepted practices of frequent hand washing with soap and water and the use of hand sanitizers.”

It is not killed by soap or alcohol-based hand sanitizers -- but it can be dislodged. The most effective prevention is to wash your hands with soap, rinse them thoroughly, and dry them with a disposable paper towel. Watch what you touch, especially banisters, elevator buttons and shared restaurant utensils. Do not rub your eyes or nose, or bite your fingernails. 

Cleaning of ships

According to the CLIA (the Cruise Lines International Association), which has a FAQ page about norovirus on ships, the cruise line industry follows a clear protocol to ensure that ships are properly cleaned. The cruise lines have a voluntary program with CDC, called the “Vessel Sanitation Program” which provides methods for the CDC to inspect and monitor cruise ship health issues. 

The CDC opened an investigation into the Crown Princess outbreak, in accordance to CLIA guidelines.  Those guidelines also require that ships that have a substantial outbreak affecting 3 percent or more of passengers (The Crown Princess was more than 4 percent) begins its “Outbreak Protection Protocol,” which includes cleaning all areas of the ship, and not allowing passengers to touch certain shared surfaces, such as food serving utensils in buffet lines. 

But these steps don’t ensure the same ship won’t be hit again. In April, 129 people on the same ship contracted norovirus during a seven-day cruise off the California coast. Lomax said that the ship went through the same stringent disinfecting process after it docked.

Passenger Rights and Insurance 

If you encounter a norovirus cruise, you have the right to leave the ship, but that is all. You are not guaranteed any compensation from the cruise line, nor can you cancel an upcoming cruise on a ship just because it has experienced a recent outbreak of norovirus. You will have to pay the same cancellation penalty you would pay if you cancel for a personal reason.

Norovirus, like most diseases, comes under the legal principle “force Majeure,” or “Acts of God.”  If you contract norovirus during a cruise, the staff will likely restrict you to your cabin for 48 hours and deliver your food and drink. The disease is uncomfortable but rarely dangerous, except in the very elderly or health compromised. 

So if you if you think it’s worth it to get travel insurance to protect against illness or cancellation, consider this: It is really good only as a protection if you happen to catch the virus onboard the ship and you incur costs because of it. 

Regular travel insurance will not allow you to cancel a planned cruise just because the ship has had an outbreak of norovirus on a previous cruise, unless you specifically buy a “Cancel for Any Reason” travel insurance policy. 

John Cook, president of QuoteWright.com, an independent online travel insurance store said, “Basically, every travel policy names certain covered “perils.” Things like lost luggage, trip interruption and medical conditions are all included.” 

Travel insurers do classify norovirus as a medical condition.  But travel insurance will only apply if the ship’s doctor charges you a fee (not usual in norovirus cases), or recommends hospitalization, then insurance should cover the medical evacuation and related expenses, although policies differ in this respect. 

“But your policy will probably limit how much compensation you can get per day for a medical issue,” Cook advised. “Flights are usually covered, but other expenses will likely be capped at about $150 per person, per day, at a maximum of five days.” 

Cook recommends saving your receipts for everything -- taxis, hotels, meals, etc. You will have to pay out of pocket and submit a claim for reimbursement later. 

Trip interruption is different, with the compensation based on a prorated per diem cost of the vacation. But if a cruise line gives the passengers compensation, then the insurance company will not see your situation as a “loss” and will not reimburse you. 

Furthermore, “pain and suffering” is not considered a peril by travel insurers, so if there is no financial loss to the policy holder the insurance company will not pay. 

Paul Motter and the Associated Press contributed to this report.