I am completely new to the haunt business, but here's my ideas for this character:
-If you have enough money, purchase one of those scent machines. Mix a few scent packets to create a horrible smell. You could mix Oak Island's Hospital, skunk, decay/compost scents. If this mixture doesn't make people realize the character is sick, may God help them.
-Maybe set up the room to make it look like the character is quarantined inside a government building. Have a path that goes along one side of the containment cell. At the end of the cell, have the path do a 180 turn and force the visitors to walk through the cell with the character.
-Maybe give the character a few warts/boils/mutations here and there. Use either green makeup on the actor's skin or use a green light to give the skin an odd color.
-For the clothes, give the character PURE white hospital-style clothes.
-Maybe have the character make a cough sound as the visitors walk by. At the same time, have "phlegm" or "blood" fly at the visitors.
_____________Like I said, I'm new to the haunt business. I've never been to a haunted house, nor have I worked for one. Just recently, I discovered my passion for scare acting. So I'm not sure how effective this room/character will be. I just poured out my ideas on a sick character. I hope I helped in some way.