Dr. Letellier treats all types of allergies (respiratory, drug-related, and food-related) in patients of all ages. He is also a specialist in internal medicine and clinical immunology, a highly multidisciplinary field that manages patients with multiple conditions, systemic and autoimmune diseases, and health assessments.Dr. Letellier treats all types of allergies (respiratory, drug-related, and food-related) in patients of all ages. He is also a specialist in internal medicine and clinical immunology, a highly multidisciplinary field that manages patients with multiple conditions, systemic and autoimmune diseases, and health assessments.