They've probably just realised Hepatitis B is a form of STD.
Anything sexual is HARAM!!
.......unless it's with a cousin.
Being the humanitarians that they are they want to spare you the trouble of coming all this way if you're a proven, diseased fornicator. Purely incidentally, this will also spare them the embarrassment of having to deal with it and some associated, indirect cost.
You'll have to take care of it yourself anyway since no DIRECT STD-related costs will be covered by the clinic. One of the (many, many) medical coverage loopholes some of the swingers here have discovered after a careless but enjoyable night out with crew.