1 Clinical Epidemiology and Medical Statistics Unit, Department of Medical, Surgical and Experimental Sciences, University of Sassari, Sassari, Italy.
2 World Health Organization Regional office for Europe, Copenhagen, Denmark.
3 International Union Against Tuberculosis and Lung Disease, Paris, France, Department of Medicine, Therapeutics, Dermatology and Psychiatry, Kenyatta University, Nairobi, Kenya.
4 Faculdade de Medicina, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil.
5 Servizio di Epidemiologia Clinica delle Malattie Respiratorie, Istituti Clinici Scientifici Maugeri IRCCS, Tradate, Italy.