Crossword Genius

Disease picked up when the impossible happened (5,3)

Ross

I believe the answer is:

swine flu

'disease' is the definition.
(swine flu is a disease)

I cannot understand how the remainder of the clue works.

(Other definitions for swine flu that I've seen before include "hazard!" , "Bug" .)

I've seen this clue in The Guardian and The Irish Times.
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