frosting with egg yolk refrigeration

Without seeing the recipe, it's very difficult to render much of an opinion. Here are some thoughts:

The odds are 20,000:1 a USDA egg is contaminated.
When in doubt, refrigerate.

I'm not much of a baker but all the buttercreams I've made (or attempted to make) have had the eggs brought to 160F during the process. I may get bashed for this statement but I see no reason to do otherwise.

It is possible there's enough sugar in the mixture to act as a preservative. See this thread (especially my last post):

http://www.food52.com/hotline/14001-must-cream-cheese-frosted-cupcakes-be-put-in-fridge

I was wodnerig whether anyone had any thoughts and also wanted to clarify that it was the frosting that was made with a raw egg yolk.