I don’t think that he just thinks about that, he must be obsessing a lot if he has OCD
. This tendency is based on unnatural fear
and will eventually lead to OCD, if it hasn’t already. There must have been some childhood experience around fear that has not been resolved and it is coming up now in this form. He must meet with a counselor along with his parents and find out where this fear originated and what the occasion was. The obsession is about hygiene and perhaps infection
that stimulates this kind of reaction. He will need to get a reality check
with a medical person to dispel
these fears and accept
that his immune system is able to fight minor infections rather efficiently. Of course he must be able to trust that source and accept it as a fact: this may take time but is a very important exercise in his therapy. He may also learn that certain amount of hygiene is essential but not extreme and any excessive forms are to be considered as OCD. They will finally cripple him if it reaches chronic states of OCD. If it has already reached difficult proportions, you may need to go on medication and the counselor will advise you so.