[1] Acad Med Ctr, Dept ENT, NL-1100 DD Amsterdam, Netherlands
[2] UCL, Sch Med, Royal Natl Throat Nose & Ear Hosp, Inst Laryngol & Otol, London W1N 8AA, England
[3] Ghent Univ Hosp, B-9000 Ghent, Belgium
[4] Free Univ Brussels Hosp, Brussels, Belgium
[5] Katholieke Univ Leuven Hosp, Louvain, Belgium
[6] Univ Uppsala Hosp, Uppsala, Sweden
[7] Univ Nottingham Hosp, Queens Med Ctr, Nottingham NG7 2UH, England
[8] Univ Hosp Sestre Milosrdnice, Zagreb, Croatia
[9] Univ Penn, Med Ctr, Dept Otorhinolaryngol Head & Neck Surg, Philadelphia, PA 19104 USA
[10] Med Univ Lodz, Fac Med, Dept Allergy & Clin Immunol, Lodz, Poland
[11] Univ Cent Hosp, Dept Otorhinolaryngol, Helsinki, Finland
[12] Inst Invest Biomed August Pi & Sunyer, Barcelona, Spain
[13] Univ Siena, Inst Discipline Otorinolaringol, Siena, Italy
[14] Karl Franzens Univ Graz, ENT Dept, Graz, Austria
[15] Cent Hosp Skovde, Dept Otorhinolaryngol, S-54185 Skovde, Sweden