Suggest Treatment For OCD Symptoms In A Teenager

hi I have a mental health question regarding my teenage son (17) he has a fear of getting sick and does these rituals for hand washing after the bathroom he always feels like his hands are dirty. we sent him to a therapist because we suspected OCD . we were told no just a fear of getting sick , he hates to throw up , his is quite thin yet he eats , very finicky eater, washes hands up to the bicep after using restroom washes hands twice, and is constantly wiping everything including himself off with alcohol wipes, he questions how we wash the laundry and the dishes ,checks expiration dates on not just food but non food items, it has pretty much halted his regular day to day activities. please is there anything we can do to help him to understand or actually to believe that he is going overboard and bordering on excessive.???