Hi.. Thanks for the query.. As per your complain bad breath also known as Halitosis can occur due to a number of causes like poor oral hygiene, oral and dental infections,post nasal drip, sinusitis, acid reflux,respiratory infections, diabetes etc.. As he has undergone Nissen surgery that is for acid reflux then first of all I would like to know that are his symptoms relieved? Also if he is on any medication? You should consult an Oral Physician or an Otolaryngologist and get evaluated and a thorough clinical evaluation and investigations depending upon suspected cause can help in diagnosis.. Treatment of underlying cause will relieve the symptoms.. As of now he should start gargling with a flavoured mouthwash twice a day.. You should chew flavored sugarfree chewing gum.. Do warm saline gargles twice a day.. Limit the intake of high aroma foods like onion and garlic.. Drink plenty of water and maintain a good oral hygiene.. Hope this helps.. Regards.