1 Institute and Policlinic for Occupational Medicine, Environmental, Medicine and Prevention Research, University of Cologne, Cologne, Germany. Electronic address: peter.morfeld@rub.de.
2 Institute and Policlinic for Occupational Medicine, Environmental, Medicine and Prevention Research, University of Cologne, Cologne, Germany.
3 Department of Medical Sciences and Public Health, Occupational, Medicine Unit, University of Cagliari, Cagliari, Italy.