Disorder of intestine, involving runs - not initially notifiable (9)
I believe the answer is:
enteritis
'disorder' is the definition.
(enteritis is a kind of disease)
'intestine involving runs not initially notifiable' is the wordplay.
I cannot quite see how this works, but
'runs' could be 'r' (cricket abbreviation) and 'r' is located in the answer.
'not' could be 'nt' ('n't' can be a synonym of 'not') and 'nt' is found in the answer.
This explanation may well be incorrect...
'of' acts as a link.
(Other definitions for enteritis that I've seen before include "tummy upset" , "gut problem" , "Inflammation of the intestine" , "complaint" , "Intestinal inflammation" .)