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. 2009 Aug;75(15):4984-92.
doi: 10.1128/AEM.00489-09. Epub 2009 Jun 12.

Prevalence and genotypes of human noroviruses in tropical urban surface waters and clinical samples in Singapore

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Prevalence and genotypes of human noroviruses in tropical urban surface waters and clinical samples in Singapore

Tiong Gim Aw et al. Appl Environ Microbiol. 2009 Aug.

Abstract

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.

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Figures

FIG. 1.
FIG. 1.
Map of the water catchment and estuarine bay located in the central of Singapore city showing sampling sites.
FIG. 2.
FIG. 2.
Phylogenetic tree based on partial nucleotide sequences of the capsid gene of environmental norovirus GI isolates. Nucleotide sequences isolated from environmental water samples are indicated in boldface and designated according to the sampling location, date, and the clone number for different genotypes. Numbers at each branch indicate bootstrap values for the clusters supported by that branch. Bootstrap values of ≥70 are shown.
FIG. 3.
FIG. 3.
Phylogenetic tree based on partial nucleotide sequences of the capsid gene of clinical and environmental norovirus GII isolates. Nucleotide sequences isolated from environmental water samples and bootstrap values were as described in the legend to Fig. 2. Nucleotide sequences of clinical samples are indicated as CL, following by the sample code. The number of identical nucleotide sequences obtained from clinical samples is listed in parentheses.

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