Sir, my son has a problem of frequent cold, cough and sore throat. this time he has cough for more than 40 days, sometimes acute, usually dry. Montaux test is normal (6X7 mm after 48 hours). Chest x-ray, abdomen USG, IgE and ESR etc are also normal. Kindly guide be what can be cause of this cough and what can be possible line of treatment.