For each infection, dropping in is ideal (10)
I believe the answer is:
perfection
'ideal' is the definition.
(perfection is a kind of ideal)
'for each infection dropping in' is the wordplay.
'for each' becomes 'per' (I've seen this before).
'dropping' indicates named letters should be taken away.
'infection' with 'in' removed is 'fection'.
'per'+'fection'='PERFECTION'
'is' is the link.
(Other definitions for perfection that I've seen before include "Faultlessness" , "Highest state" .)