It would never have occurred to me that the host parent would call me to let me know that someone might have a cold ... ?

If I was pregnant / immuno-compromised / particularly worried about the risk, then *I* would call *them* to check.

Personally, I think that going to any party (park, home, playcentre, pool, whatever) or any gathering of people - kids or otherwise - has an inherent risk of bugs.

I've caught as many colds in Drs waiting rooms, trains and at work as I have anywhere else. C'est la vie.

JMO.