See Irish American as source of complaint (5)
I believe the answer is:
virus
'source of complaint' is the definition.
(a virus might cause a medical complaint)
'see irish american' is the wordplay.
'see' becomes 'v' (short for 'vide', Latin meaning 'see elsewhere').
'irish' becomes 'IR' (abbreviation).
'american' becomes 'US' (United States).
'v'+'ir'+'us'='VIRUS'
'as' is the link.
(Other definitions for virus that I've seen before include "Microscopic infectious agent" , "Harmful computer code" , "Submicroscopic organism, cause of disease" , "Pathogenic agent" , "Infectious particle" .)