1 Inserm U1219, Institut de Santé Publique, d'Epidémiologie et de Développement, Bordeaux School of Public Health, Université de Bordeaux, CHU de Bordeaux, Bordeaux, 33000 France. Electronic address: [email protected].
2 University of California, San Francisco, Department of Epidemiology and Biostatistics, San Francisco, CA, USA.