[1] Karolinska Univ, Hosp Solna, Dept Med, S-17176 Stockholm, Sweden
[2] Univ London Imperial Coll Sci Technol & Med, London, England
[3] Sahlgrens Univ Hosp, Gothenburg, Sweden
[4] Nordiska Halsovardshogskolan, Gothenburg, Sweden
[5] City Hosp, Birmingham, W Midlands, England
[6] Queen Marys Sch, London, England
[7] Radcliffe Infirm, Oxford OX2 6HE, England
[8] Ulleval Hosp, Oslo, Norway
[9] Univ Hosp, Reykjavik, Iceland
[10] Univ Glasgow, Glasgow, Lanark, Scotland
[11] HS Frederiksberg Hosp, Frederiksberg, Denmark
[12] Univ Cent Hosp, Helsinki, Finland
[13] Beaumont Hosp, Dublin 9, Ireland