||Norovirus (NV) is considered as one of the most important agents causing acute viral gastroenteritis and is transmitted via fecal- oral route. Norovirus-related infections can occur to beach visitors by contrasting contaminated recreational waters. The aims of this study were (1) to validate the most efficient method on viral particle recovery; (2) to monitor Norovirus and some indicator microorganisms in the sea water for one year in the north-eastern Taiwan; and (3) to compare the isolated Norovirus strains, from the environments and those prevailing in clinics, using phylogenic analysis.
Among ten filtration combinations, adsorption on nitrocellulose membrane, followed by acid rinse consistently gave the best recovery efficiency (100.00％). In the use of RT-seminested PCR, fifty-seven of the 270 stool specimens were shown as positive, with 23 (8.52%) for NVGI and 38 (14.07%) for NVGII respectively. Compared to the RT-PCR results, the detection sensitivity was increased by approximate 5% in the addition of seminested PCR (p<0.05, Pair t-test). As for the field samples, NVGII was the predominant strain (21.47%) whilst NVGI had 13.50 %.
According to the standard pollution classification system using total coliform, E. coli and enterococci as factors, the correlation between the presence of enterococci and detectable norovirus was significant with Kendale’s tau-b analysis (p＜0.05). Therefore, enterococci can be not only a suitable indicator for water quality but also an alternative factor to evaluate the distribution of Norovirus in sea water, especially in summer. The presence of Norovirus was significantly correlated to the temperature and negatively correlated with pH value of water samples. However, no correlation was found between the presence of Norovirus and the concentration of microbial indicators. This may due to some indirect factors, such as the sunshine exposure and increasing temperature.
According to the phylogenetic analysis, NVGI isolates were belonged to GI-7 group and the clinical and the environmental strains were more closely related to Japan 1999 and Taiwan 2003 outbreak. NVGII isolates from sea water samples were belonged to GII-4(2006b). All isolates either from stool specimen or sea water samples were separated as two groups (Recombinanted strain and 2006b). The recombinanted GII strains were grouped to GII-4 according to the RdRp gene and closely related to Japan 1998 prototype (Saitama U1). Furthermore, the other group, GII-4(2006b), was more closely related to the predominant strains in Japan 2006 and China 2007 outbreak.
To sum up, the GII-4(2006b) strains were cocirculated in clinical patients and in sea water in Northern Taiwan. The opportunistic Norovirus may spread in Eastern Asia.