You should definitely steam clean it and disinfect it.
Either have it prof cleaned by a carpet cleaning co or rent the machine and do it your self.
here is a tutorial! http://www.bondrewards.com/how-to-clean-a-used-mattress/
Hi Naomi - This article is how to clean a mattress in 5 easy steps. Hope this helps! Hugs, Holly
PS - We have a FREE eBook with recipes for all of my homemade and all-natural cleaners. You can download it here --> https://pinkfortitude.com/thank#GreenClean
Here's a really comprehensive post