How posh people used to pronounce actually spread disease (6)
I believe the answer is:
infect
'spread disease' is the definition.
(infect someone with a disease)
I don't understand how the remainder of the clue works.
(Other definitions for infect that I've seen before include "Contaminate with disease" , "Impart a disease" , "Transmit disease to another" , "Cause sickness (with a virus)" , "Taint with disease" .)