The U.S. State Dept. has issued the following:
U.S. citizens, particularly travelers with underlying
health conditions, should not travel by cruise ship. CDC notes
increased risk of infection of COVID-19 in a cruise ship
environment. In order to curb the spread of COVID-19, many
countries have implemented strict screening procedures that
have denied port entry rights to ships and prevented passengers
from disembarking. In some cases, local authorities have
permitted disembarkation but subjected passengers to local
quarantine procedures. While the U.S. government has
evacuated some cruise ship passengers in recent weeks,
repatriation flights should not be relied upon as an option for
U.S. citizens under the potential risk of quarantine by local
authorities.
Source: travel.state.gov
See also CDC Interim Guidance for Ships on Managing Suspected Coronavirus Disease 2019
There are around 6 ships worldwide now waiting for port - some with cases, some just denied port because people on the boat are from areas like Italy and Iran.