Possible Clues:

• Infectious disease
• Mark allowed that high temperature could indicate infectious disease
• Allow blemish to come first always, after following disease
• Disease causing rash
• Complaint made by clever RAF set
• Mark allowed in any case, after loud complaint
• Infectious disease of children
• Infectious disease producing rash
• Disease? There's mark left unfortunately, always
• Mortification sickness perhaps for Pimpernel with a cold