Taking your rat out into public

What are everyones thoughts on taking your rats out into public? I don't want to be paranoid but I worry about other people making my rats sick! lol! You never know who has rats or other animals that are sick. I never take my dog into the petsmart or petco stores because people take their animals in there, you never know what dogs have been vaccinated, etc.

Now I'm thinking the same thing about my rats, I've almost taken them with me to the petstore a few times but then I think "if I were to bring one of these rats home, I'd quarantine him for like a month first before I stuck him with my boys, why on earth would I bring my boys directly into the same building as them?"

Am I just being paranoid? Or are there others who won't take their ratties out to stores with them. We go outside a lot, and I'll take them to the store with me, sometimes they hide in my purse ... lol ...