Well, for starters, you table design needs work.
NEVER use a TEXT column unless you *MUST*.
Certainly never for something like itemid or userid.
TEXT columns are VERY expensive to store in the DB *and* they are even worse for querying against. They can't be indexed, for example.
Anyway, are you looking for a list by both itemid and userid of how many have not been read? Or just for one specific itemid/userid?
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.