Guy's: key hospital for injection and nursing, with fear of epidemic maybe (6,5)

'fear of epidemic maybe' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'guy's key hospital for injection and nursing' is the wordplay.
I cannot quite understand how this works, but
'key' could be 'alt' (the Alt keyboard button) and 'alt' is present in the answer.
'hospital' could be 'h' (abbreviation for hospital on maps) and 'h' is present in the answer.
'nursing' could be 'care' (I've seen this in another clue) and 'care' is found in the answer.
The remaining letters 'ehs' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

'with' is the link.

Can you help me to learn more?