I suggest sprinkling baking soda over the whole carpet, unless you can find the spot. Then let it sit a half hour to an hour. Then vacuum it up. You can repeat this if the smell doesn't go away. When this happened with my son, I could get the spot right away so I used vinegar/water or simple green.
If you rewet the area it will bring the smell back, but if you are cleaning with the vinegar solution it should take care of it. I just have never put vinegar into my carpet shampooer, though I don't think it would hurt anything.
You might try washing the lower portion of the walls with vinegar/water also, in case it got there. I forget the ratio, maybe 4v:1w?
These cleaners should take care of it, you shouldn't have to buy anything special.