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A top cruise line is taking new measures to keep coronavirus off its ships and to keep passengers happy -- but even sick guests and those who have traveled in impacted countries are encouraged to return ... once they've recovered, of course.

Carnival Cruise Line -- one of the 9 cruise brands under the Carnival Corp. umbrella -- tells TMZ ... it's implemented an enhanced screening process due to concerns over coronavirus, and guests who are deemed unable to board at the terminal will get all their money back.

On top of that, we're told the sick guests will be reimbursed for transportation, and bonus -- they'll also get a 20 percent credit for a future cruise. A pretty decent consolation.

As for other safety precautions ... CCL says it's worked with the CDC and the World Health Organization to update screening procedures. Additionally, anyone who's traveled to China, Hong Kong, South Korea or Macau within 14 days of their cruise's scheduled departure will not be allowed to set sail.

Meanwhile, Crystal Cruises are also offering ill or restricted passengers an option plan -- 100 percent refund or a 125 percent future cruise credit -- but ONLY if they notify Crystal within 7 days of departure. Otherwise, we're told there could be cancelation fees.

The cruise industry, in particular, is taking coronavirus very seriously after a Princess Cruise liner was quarantined for 2 weeks earlier this month with 3,700 passengers on board. The ship was isolated in Japan's Yokohama Bay when at least 700 guests were reportedly diagnosed with the virus. They were eventually evacuated, but 4 of them have died.