Clin. Lab. 3+4/2013 271 Clin. Lab. 2013;59:271-276 ©Copyright ORIGINAL ARTICLE Emergence of Norovirus GII/4 2006a and 2006b Variants in Hospitalized Children with Acute Gastroenteritis in Thailand AKSARA THONGPRACHUM 1,2 , PATTARA KHAMRIN 3 , WISOOT CHAN-IT 1 , RUNGNAPA MALASAO 3 , NATTHAWAN CHAIMONGKOL 3 , SHOKO OKITSU 1,2 , MASASHI MIZUGUCHI 1 , NIWAT MANEEKARN 3 , SATOSHI HAYAKAWA 2 , HIROSHI USHIJIMA 1,2 1 Department of Developmental Medical Sciences, School of International Health, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan 2 Division of Microbiology, Department of Pathology and Microbiology, Nihon University School of Medicine, Tokyo, Japan 3 Department of Microbiology, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand SUMMARY Background: Norovirus (NoV) is recognized as a significant cause of acute gastroenteritis in infants and young children worldwide. This study investigated the prevalence of NoV infection in hospitalized children with gastro- enteritis in Chiang Mai, Thailand in 2006. Methods: A total of 156 fecal specimens were collected from children with diarrhea admitted to McCormick Hos- pital in 2006. All fecal specimens were examined for NoV by RT-PCR and the genotypes were identified by se- quence analysis. Results: A high prevalence of NoV infection was detected (20.5%, 32/156). NoV GII/4 was the most predominant genotype with a prevalence of 87.5% (28/32), while GII/3, GII/6, GII/12, and GII/15 were less common (3.1% each). Among GII/4 strains, 2006b variant (75%, 21/28) emerged as the leading strain and dominated over the Hunter’04-like variant, which was the most common strain in the previous season of 2005. In addition, the 2003, 2004, and 2006a variants were also detected. NoV infections were most commonly observed in the rainy season in Thailand. Conclusions: This study demonstrated the emergence of GII/4 2006b variants as the major pathogen causing acute gastroenteritis among infants and children at the age of less than 5 years old who admitted to hospital in Chiang Mai, Thailand in 2006. Additionally, other GII/4 variants of 2003, 2004, and 2006a were also reported. (Clin. Lab. 2013;59:271-276. DOI: 10.7754/Clin.Lab.2012.120316) KEY WORDS norovirus, Thailand, 2006b variant, gastroenteritis INTRODUCTION Norovirus (NoV) is recognized as the most common eti- ological agent responsible for gastroenteritis outbreaks worldwide. NoV is a member of the Caliciviridae fami- ly which contains a positive sense single-stranded RNA genome, approximately 7.7 kb in size. Based on the va- riations in the capsid gene sequences, NoV can be ge- netically classified into 5 genogroups (GI-GV), of which three have been found in humans; GI, GII, and GIV [1,2]. The NoV genogroups detected in humans have been further subdivided into at least 8 genotypes in GI, 17 genotypes in GII, and only one genotype in GIV [1,2]. Several epidemiological studies have reported that NoV GII/4 genotype is the most predominant genotype cir- culating in many epidemiological settings worldwide [3-6]. Recent molecular surveillances reveal that capsid sequences of GII/4 strains have evolved over the last 20 years and continue changing with new variants emerg- ing every two or three years [7,8]. Several NoV GII/4 variants have been widely classified according to the year of detection as novel GII/4 variants of 1996, 2002, _____________________________________________ Manuscript accepted June 1, 2012