1. Otorhinolaryngology Department, Speciality Hospital No 71, Social Security Mexican Institute, Torreón, Coahuila, México
2. Medical Research Unit in Clinical Epidemiology, Speciality Hospital No 71, Social Security Mexican Institute, Torreón, Coahuila, México
3. Clinical Immunology and Allergy Department, Speciality Hospital No 71, Social Security Mexican Institute, Torreón, Coahuila, México