On Wednesday, nearly 3,700 people onboard Genting’s World Dream cruise were being held on the ship and undergoing testing for coronavirus.

Three people who were on the ship from Jan. 19 to Jan. 24 have tested positive for coronavirus, according to a letter to guests from Dream Cruises, which operates the ship. As a result, Taiwan’s government blocked the ship’s port of call in Kaohsiung and forced its return to Hong Kong on Wednesday. There are 1,871 passengers and 1,820 crew members onboard.

Edith Poon, spokesperson for Genting Hong Kong Limited, the holding company that owns Dream Cruises, confirmed that 30 crew members self-declared symptoms of the virus. "We are currently waiting for the results to come in," she told USA TODAY. "Upon availability of the results, we shall comply with the Department of Health's instruction on the next step forward. Until then, as advised by the Department of Health, all passengers of the cruise ship are to remain onboard."

Common signs of infection include fever, cough, shortness of breath and breathing difficulties.

“We would like to inform you that all passengers had received stringent temperature checks in Guangzhou Nansha upon disembarkation,” per the letter to guests. “At that time, all passengers tested returned negative results."

Poon noted that all passengers of the ship must undergo temperature checks and other health screen before people will be allowed to disembark.

There have been more than 24,600 cases diagnosed worldwide, with all but 216 coming from mainland China and Hong Kong and the rest spread across more than 20 countries. Nearly 500 have died and about 1,000 have recovered.

Diamond Princess quarantined for 14 days after 10 positive tests

The World Dream is the third cruise ship to be placed under quarantine in the past week.

On Wednesday, Princess Cruises announced that the 3,700 people aboard the Diamond Princess will remain under quarantine at sea for two weeks after Japanese health officials diagnosed 10 people with coronavirus.

"These 10 persons, who have been notified, … will be taken ashore by Japanese Coast Guard watercraft and transported to local hospitals for care by shoreside Japanese medical professionals," Princess Cruises said in a statement provided by spokesperson Alivia Owyoung.

"The ship plans to go out to sea to perform normal marine operations including, but not limited to, the production of fresh water and ballast operations before proceeding alongside in Yokohama where food, provisions, and other supplies will be brought onboard," the statement added. "Guests will continue to be provided complimentary internet and telephone … the ship’s company is working to keep all guests comfortable."

The cruise line added that they will "continue to fully cooperate with and follow the instructions of global medical authorities and the Japanese government."

The ship had already been held outside the port Tuesday in Yokohama, Japan, for 24 hours while medical professionals ran tests on guests and crew after a passenger from Hong Kong was diagnosed at a hospital during a port call there.

False alarm on Costa Smeralda

Costa Cruises had its own scare on Jan. 30 when a female Chinese passenger aboard the Costa Smeralda displayed symptoms. The ship was held in quarantine off the coast of Italy while health officials ran tests on her and her traveling companion. In the end, she was diagnosed with the common flu and the rest of the passengers were allowed to disembark in the city of Civitavecchia.

Cruise lines beef up screening, cancel cruises and port calls in China

After the World Health Organization declared coronavirus a global health emergency on Jan. 30, the trade group Cruise Lines International Association announced new guidelines. Its 270 member ships pledged to deny boarding to any passenger or employee who had been in mainland China in the past 14 days.

Coronavirus: Cruise ships to deny boarding to anyone who has recently been in China

Some cruise lines, including Royal Caribbean and Celebrity, went further in their screening efforts, saying no one who had been to Hong Kong in the past 15 days could board their ships, either. Royal Caribbean also said that anyone holding a passport from China or Hong Kong would be subject to additional health screenings regardless of the last time they were there. Cruise & Maritime Voyages has announced it wouldn't allow anyone who had been to mainland China in the past 30 days to board.

Royal Caribbean also canceled eight China cruises, joining other lines that have scrapped sailings or port calls to the country where the epidemic began in late 2019.

The following companies have either canceled entire cruises, moved embarkation or disembarkation ports or replaced port calls to China or Hong Kong with stops in other nearby countries: Azamara, Costa Cruises, Celebrity Cruises, Crystal Cruises, Cunard Line, Dream Cruise Line, Holland America, MSC Cruises, Princess Cruises, Seabourn, Silversea and Star Cruises.

Coronavirus: The latest on cruise line cancellations and policy changes

How to stay healthy on a cruise

Wash your hands often and use hand sanitizer. The Centers for Disease Control says this is still the best defense against picking up viruses at sea or on land. Also avoid touching your eyes, nose and mouth if you haven't washed your hands lately.

Cough or sneeze into a tissue. And then dispose of the tissue immediately.

Clean your cabin's surfaces. Cruise Critic suggests bringing disinfecting wipes or household cleaner so you can wipe down the common surfaces in your stateroom, like tables, desk and balcony furniture. Then head to the bathroom faucets and toilet seat as well as door handles and light switches. And go over the TV remote and cabin phone while you're at it.

Remove any decorative bedding. While the housekeepers change the sheets and pillowcases regularly, the same doesn't go for bedspreads and decorative pillows. Cruise Critic recommends stashing them in the closet or asking your cabin steward to remove them for the duration of your cruise.

Protect yourself before leaving home

But the most important thing you do can do to protect yourself during a trip should occur well before you head to the airport or cruise terminal: research.

Look at your medical insurance in advance to identify any coverage gaps. Research how your health insurance policy covers illness or injury while traveling well in advance of boarding. Does it cover you in the event of medical emergencies while on the ship or in foreign countries? Does it include medevac services? If your policy does not – or if you are a senior who depends on Medicare, strongly consider purchasing a travel medical insurance policy.

Check your travel insurance policy, too. Don't assume your travel insurance will cover everything if you get sick or injured, either. For travel to developed countries, SmarterTravel estimates that $50,000 in medical and $50,000 medevac would be adequate coverage. Travel to less developed areas, however, might call for slightly higher limits. It’s ultimately your call.

Research your cruise line's medical services. In light coronavirus, the Cruise Lines International Association members have committed to staffing their infirmaries around the clock to provide initial care for the time being.