Songster's throat infection (6)
I believe the answer is:
thrush
This clue is a double definition.
'songster's' is the first definition.
(I've seen this before)
'throat infection' is the second definition.
(I've seen this before)
(Other definitions for thrush that I've seen before include "Brown songbird" , "Songbird with brownish back and speckled breast" , "Common British songbird" , "Bird that sings" , "Speckle-breasted songbird" .)