Molecular epidemiology of norovirus gastroenteritis in Soma, Japan, 2001–2003

Abstract

The aim of the present paper was to investigate the molecular epidemiology of norovirus gastroenteritis in Japan using polymerase chain reaction (PCR) and subsequent phylogenetic analysis. From September 2001 to August 2003, 515 stool samples or rectal swabs were collected from almost all children visiting the Department of Pediatrics, Public Soma General Hospital with gastroenteritis. Samples were examined on reverse transcription (RT)-PCR to detect norovirus genome. The nucleotide sequences of the PCR products were determined and phylogenetic analysis performed. The norovirus genome was detected in 66 samples. The peak season of norovirus gastroenteritis was from November 2001 to February 2002 and from September 2002 to December 2002. Norovirus gastroenteritis occurred most frequently in 1-year-old children. Norovirus strains produced four distinct clusters on phylogenetic analysis. Some strains detected in Soma were closely related to the strains detected in other regions in the world. The Mexico type and Lordsdale type were predominant in the 2001/2002 and 2002/2003 seasons, respectively, and the outbreaks continued for several months. Genetically different noroviruses might cause repeated gastroenteritis outbreaks every year in the Soma area. The long duration of the outbreak by a predominant strain in an epidemic season and the prevalence of infection mainly in the young age group suggested that norovirus epidemics were caused by person-to-person transmission rather than foodborne transmission. Based on molecular epidemiology, it is suggested that the annual prevalence of norovirus gastroenteritis in the Soma area might be caused by person-to-person transmission of genetically different norovirus strains, which might be transmitted from other region in the world.