The flu spreading around area is nasty (7)
I believe the answer is:
hateful
'nasty' is the definition.
(similar in meaning)
'the flu spreading around area' is the wordplay.
'spreading' indicates anagramming the letters.
'around' indicates putting letters inside.
'area' becomes 'a' (maths abbreviation).
'the'+'flu'='theflu'
'theflu' anagrammed gives 'hteful'.
'hteful' enclosing 'a' is 'HATEFUL'.
'is' acts as a link.
(Other definitions for hateful that I've seen before include "Detestable" , "Dreadful" , "Unpleasant" , "repellent" , "Abhorrent" .)