A month in charge of preventing infection (7)
I believe the answer is:
aseptic
'preventing infection' is the definition.
(aseptic means excluding infectious microorganisms)
'a month in charge' is the wordplay.
'month' becomes 'sept' (Sept is an example).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'a'+'sept'+'ic'='ASEPTIC'
'of' is the link.
(Other definitions for aseptic that I've seen before include "avoiding germs" , "Free from bacteria, surgically clean" , "ideal conditions for hospital?" , "Free from harmful bacteria" , "Sterile" .)