how common is salmonella?

Question
Hi,
I have agreed to do my friend a favor and watch her turtle for 4 months.  The turtle is pretty large (5x4"?) but I don't know what kind of turtle it is.  

I have a dog that I adore, he has been through a lot and is recovering from illness.  After a general turtle info search, I read that they can have salmonella.  Now I'm terrified that my dog will get this from the turtle.  I asked my friend and she said the turtle has never been to the vet.  Is there a test that can be done on the turtle to rule salmonella out before I take it? Should I be worried?  

Thank you.

Answer
Hello It is common in red ear slidders under 4 inches. As long as  you wash your hands before and after handeling, and you wash after handling any of the turtles items water includesd, and do not let it roam by your dog it should be fine. They can have a fecal done to establish risk.