Infected? No admittance unfortunately (12)
I believe the answer is:
contaminated
'infected?' is the definition.
(infecting is a kind of contaminating)
'no admittance unfortunately' is the wordplay.
'unfortunately' indicates an anagram (a bad or unfortunate spelling).
'no'+'admittance'='noadmittance'
'noadmittance' anagrammed gives 'CONTAMINATED'.
(Other definitions for contaminated that I've seen before include "Made impure" , "infected" , "Polluted - anatomic dent (anag)" , "Bad" , "No longer pure" .)