1. Centre for Enteric Pathogens of Southern Italy (CEPIM), Dipartimento di Igiene e Microbiologia "G. D'Alessandro", University, Palermo, Italy
2. U.F. Biotossicologica, Azienda USL3, Pistoia, Italy
3. Centre for Enteric Pathogens of Northern Italy (CEPIS), University, Milan, Italy
4. Istituto Zooprofilattico Sperimentale della Sicilia "A. Mirri", Palermo, Italy
5. Dipartimento di Sanità Pubblica, University, Florence, Italy