Background: Noroviruses are common pathogens in human gastroenteritis outbreaks worldwide. They belong to a genetically diverse group of RNA viruses with multiple genogroups (G) and genotypes. Genotype GII-4 norovirus (Lordsdale) is the predominant agent in epidemics.
Objectives: To investigate the genetic variation in GII-4 strains isolated during seven epidemic seasons in Hungary from November 2000 to June 2007.
Study design: Using the prospective epidemiological surveillance of norovirus outbreaks in Hungary, GII-4 strains were selected for further genetic analysis. After phylogenetic analysis, RNA-polymerase (open reading frame 1; ORF1), capsid (ORF2) and the ORF1/ORF2 junction were analysed by RT-PCR and sequencing.
Results: Three hundred and seventy-seven (76.8%) of 491 confirmed norovirus outbreaks were caused by genotype GII-4. GII-4 was the predominant genotype in six of the seven epidemic seasons. Four main GII-4 variants--epidemic point mutants--(GII-4-2000, GII-4-2002, GII-4-2004 and GII-4-2006b) were detected, with each variant predominating in two consecutive epidemic seasons.
Conclusions: Genotype GII-4 was confirmed as the predominant genetic type in epidemic norovirus seasons in Hungary. Genetic drift successfully promotes the re-emergence of GII-4 variants in the population. The elevated number of norovirus outbreaks in the population predicts the emergence of new GII-4 genetic variants as part of an international epidemic.