[1] Univ Gothenburg, Sahlgrenska Acad, Inst Clin Sci, Dept Otorhinolaryngol Head & Neck Surg, Grona Straket 9, S-41345 Gothenburg, Sweden
[2] Sahlgrens Univ Hosp, Dept Otorhinolaryngol, Reg Vastra Gotaland, Gothenburg, Sweden
[3] Telemark Hosp, Dept Occupat & Environm Med, Skien, Norway
[4] Univ Oslo, Inst Hlth & Soc, Dept Community Med & Global Hlth, Oslo, Norway
[5] Univ Gothenburg, Sahlgrenska Acad, Inst Med, Occupat & Environm Med, Gothenburg, Sweden