hi i had gone through your query and understand your concerns.i would come up with the possibility of LOW IMMUNITY or DECREASED RESISTANCE POWER may be the cause for your grand father redcurrant cellulitis
other possible causes include;
-anaerobes should be suspected.
-There may be an obvious portal of entry for infection such as a recent abrasion or a venous leg ulcer. The web spaces of the toes should be examined for evidence of fungal infection
is best done serologically by streptococcal titres: antistreptolysin O titre (ASOT) and antiDNAse B titre (ADB).
i advise you taking Homeopathic
medicines gives safe and permanent cure for your grand father cellulitis complaints
consult your local homeopathic physician for correct diagnosis of the case and remedy to fit his complaints
I hope this is helpful for you, thank you