If you have no infection on board, and you have appropriate equipment for testing temperature, you
can always insist that you take everyone’s temperature prior to coming on board.
If not, then you can always insist that your crew stay more than a meter from anyone visiting from outside.
If you do have an infected person on board, then this should be notified to the relevant Authorities and it is extremely unlikely that anyone other than medical specialist will want to come on board.