[1] IST SUPER SANITA,DEPT EPIDEMIOL,I-00161 ROME,ITALY
[2] IST SUPER SANITA,DEPT VIROL,I-00161 ROME,ITALY
[3] UNIV PADUA,DEPT GASTROENTEROL,I-35100 PADUA,ITALY
[4] UNIV MODENA,DEPT GASTROENTEROL,I-41100 MODENA,ITALY
[5] UNIV TRIESTE,DEPT INTERNAL MED,I-34100 TRIESTE,ITALY
[6] UNIV PALERMO,DEPT INTERNAL MED,I-90134 PALERMO,ITALY