On that note I suggest that the UI should have the following three "states":

1/ New article, never read:

    22 comments

I know that they are all unread, don't need to tell me.

2/ Visited article

    25 comments (3 unread) 

This is nicer IMHO than having another | separator. The 3 unread could be bold as it is now.

3/ Visited and all read:

    25 comments (0 unread) 

But this time 0 unread does not need to be bold.