1. John Hopkins University; General Internal Medicine; Baltimore MD USA 21287
2. Temple University Hospital; Department of Internal Medicine; Philadelphia USA
3. University of Zurich; Institute of General Practice; Zurich Switzerland 8091
4. Centre for Research in Environmental Epidemiology (CREAL); Doctor Aiguader 88 Barcelona Spain 08003
5. Hospital del Mar Research Institute (IMIM); Barcelona Spain
6. CIBER Epidemiología y Salud Pública (CIBERESP); Barcelona Spain
7. University of Pompeu Fabra; Department of Experimental and Health Sciences; Barcelona Spain
8. Johns Hopkins Bloomberg School of Public Health; Epidemiology; 615 Wolfe Street Mail room W5010 Baltimore MD USA 21205