An old-fashioned case, we’re told, of flu (6)

I believe the answer is:

grippe

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'flu' is the definition.
(I know that flu can be written as grippe)

I don't understand the rest of the clue.

(Other definitions for grippe that I've seen before include "infection" , "'flu, as before" .)

I've seen this clue in the Evening Standard.

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