If you are in Port or Port anchorage, you should immediately report the occurrence to the Port Authorities and isolate the individual concerned in a cabin having taken his temperature. The Port Authorities will then provide advice on what to do next depending upon their facilities and abilities to deal with the virus. The office should be kept advised of all communications.
If the Port will not take the sick seafarer to a medical facility, then you will have no choice but to keep the individual isolated and follow issued onboard precautions