[1] Univ Bergen, Dept Clin Sci, POB 7804, N-5020 Bergen, Norway
[2] Haukeland Hosp, Dept Occupat Med, POB 1400, N-5021 Bergen, Norway
[3] Wake Forest Sch Med, Div Publ Hlth Sci, Dept Epidemiol & Prevent, Med Ctr Blvd, Winston Salem, NC 27157 USA
[4] Univ N Carolina, Dept Med, Chapel Hill, NC 27599 USA
[5] Univ N Carolina, UNC Gillings Sch Global Publ Hlth, CB 7445,404A Rosenau Hall,421 Pittsboro St, Chapel Hill, NC 27599 USA