Jack and David huge in Kildare and sick in hospitals (5,7)

I believe the answer is:

giant-killers

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'huge in kildare and sick in hospitals' is the definition.
I know nothing about this answer so I can't judge whether this works.

'jack and david' is the wordplay.
'jack' becomes 's' (I can't justify this - if you can you should believe this answer much more).
'and' says to put letters next to each other (I've seen this in other clues).
'david' becomes 'giantkiller' (I've seen this before).
's' after 'giantkiller' is 'GIANT-KILLERS'.

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I've seen this clue in the Irish Times.

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