hi i've read about this recently on one of the yahoo groups. there was a fantastic article but as far as i was aware the actual cat showed no symptoms, it was only apparent when there were problems with breeding & problems keeping the kittens alive.
here's the article for you, with some links which are all useful. hope it's some help to you. i just found a good article in my favourites from doctor susan little too ( a well respected cat specialist).
http://www.kittykouch.com/articles/gstrep.html
http://www.kittykouch.com/articles/gstrepupdate.html (part 2)
http://catvet.homestead.com/Strep.html