In poor health bearing note: it's catching (7)
I believe the answer is:
nailing
'catching' is the definition.
(I've seen this before)
'in poor health bearing note' is the wordplay.
'in poor health' becomes 'ailing' (an ailing person is unwell).
'bearing' is a charade indicator (letters next to each other).
'note' becomes 'n' (abbreviation).
'ailing' put after 'n' is 'NAILING'.
'it's' is the link.
(Other definitions for nailing that I've seen before include "Fixing" , "Catching" , "Tacking" , "Securely pinning" , "Securing" .)