One of the cruise ships that has received attention in the media is MS Zaandam. On board there are over 100 passengers with flu-like symptoms. Four people have already died, including a Swedish man.

MS Zaandam left Buenos Aires on March 7, but was ported in South America and is now heading for Florida. But even there it seems to be difficult to get ashore. Florida's governor refuses to authorize the ship.

Trump promises to help

For the more than 1,000 passengers on board now stands the hope of US President Donald Trump. The president has promised that he will talk to Florida's governor. In the US, health issues are regulated at the local and state levels.

- Here a conflict arises between the different levels of the American system. It's hard to know who's winning here. But the president can turn to a federal court that can issue a temporary decision that the authorities must follow, says Dag Blanck, professor of North American Studies at Uppsala University.

Sweden: "We have an obligation to receive"

Who decides whether a ship may call a port or not switch from country to country. In many of the countries that have closed their ports, it is the governments that make that decision.

In Sweden, there are eight so-called quarantine ports for receiving vessels with contamination. Here, each region's infection prevention physician assesses what to do when a vessel arrives.

"We have an obligation to receive vessels that have declared suspected infection on board," says Ingrid Hansson, communicator at Stockholm's ports, which is one of Sweden's quarantine ports.

Not possible to deny

To completely deny a ship to call a Swedish quarantine port does Ingrid Hansson do not see as possible according to current laws.

- I find it very difficult to imagine. We have no information that this would have happened.

Nor does Ingrid Hansson see that a cruise ship will be arriving in Stockholm's ports in the near future.

- Most people who usually come to Sweden with cruise ships: Americans, Englishmen and Germans are quarantined in their home countries. The vessels that would come to Stockholm's ports in April-May have already suspended their traffic given the situation.