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Applied and Environmental Microbiology, August 2009, p. 4984-4992, Vol. 75, No. 15
0099-2240/09/$08.00+0     doi:10.1128/AEM.00489-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Prevalence and Genotypes of Human Noroviruses in Tropical Urban Surface Waters and Clinical Samples in Singapore {triangledown}

Tiong Gim Aw,1* Karina Yew-Hoong Gin,1 Lynette Lin Ean Oon,2 Eileen Xueqin Chen,2 and Chee Hoe Woo3

School of Civil and Environmental Engineering, Nanyang Technological University, Singapore,1 Department of Pathology, Singapore General Hospital, Singapore,2 Technology and Water Quality Office, Public Utilities Board, Singapore3

Received 27 February 2009/ Accepted 29 May 2009

The prevalence and genotypes of norovirus genogroup I (GI) and GII in tropical urban catchment waters and an estuarine bay were studied. A comparative analysis was performed with environmental isolates of noroviruses and concurrently identified clinical isolates in Singapore during gastroenteritis outbreaks between August 2006 to January 2007. Noroviruses in environmental water samples were concentrated by using ultrafiltration techniques and then analyzed by reverse transcription-seminested PCR assay targeting the partial capsid region of noroviruses and DNA sequencing. Among the 60 water samples collected, noroviruses were detected in 43 (71.7%) of these samples. Of these 43 norovirus-positive samples, the coexistence of both GI and GII strains was identified in 23 (53.5%) water samples. The phylogenetic analysis revealed multiple genotypes of noroviruses GI and GII in environmental water samples. GI and GII strains were clustered into seven and nine (including two unclassified) genotypes, respectively. The major norovirus genotypes in environmental water samples were GI/2 and GI/4 and GII/4. Genotyping of the 21 norovirus-positive clinical samples showed that all of the strains belonged to the GII/4 cluster. The environmental and clinical norovirus GII/4 isolates showed high levels of nucleotide sequence identity to each other and to the novel GII/4 variant associated with global epidemics of gastroenteritis during 2006. This study suggests the emergence and circulation of multiple novel norovirus GI and GII genotypes in water environments. Further comprehensive surveillance of water environments for noroviruses and routine clinical reporting is warranted.

* Corresponding author. Mailing address: School of Civil and Environmental Engineering, Nanyang Technological University, Block N1, #B3b-18, 50 Nanyang Avenue, Singapore 639798. Phone: 65 6790 5948. Fax: 65 6791 9394. E-mail: tgaw{at}pmail.ntu.edu.sg

{triangledown} Published ahead of print on 12 June 2009.

Applied and Environmental Microbiology, August 2009, p. 4984-4992, Vol. 75, No. 15
0099-2240/09/$08.00+0     doi:10.1128/AEM.00489-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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