Phylogenetic analysis of rubella virus isolated during a period of epidemic transmission in Italy, 1991-1997.

To study the molecular epidemiology of rubella virus during endemic transmission, phylogenetic analysis of the nucleotide sequence of the E1 gene was done with 31 isolates collected in northern Italy during 1991-1997, a period spanning 3 epidemics. The viruses segregated into distinct genotypic strains. Cocirculation of genotypic strains was detected; however, each epidemic was associated with specific strains, and strain displacement occurred concomitantly with each epidemic. Although most of the viruses from Italy belonged to rubella genotype I and many were related to viruses isolated concurrently in other European countries, 3 viruses belonged to rubella genotype II, which previously had been isolated only in Asia. Thus, intercontinental importation of viruses also occurred.