To elucidate the importance of the norovirus and other enteric viruses, and the difference of the genetic relatedness on norovirus between the outbreak and sporadic cases, a total of 557 stool samples, consisting of 503 sporadic cases and 54 samples of 4 outbreaks were collected and tested for norovirus and other enteric viruses in Beijing, China, July 2007–June 2008. The data showed norovirus, rotavirus, astrovirus, and sapovirus, were detected in 26.6%, 6.1%, 1.8%, and 0.5%, respectively. Norovirus was detected almost throughout the surveillance period, norovirus co-infecting with rotavirus, astrovirus, and sapovirus, respectively, were identified both in outbreak and the sporadic cases. GII.4/2006 was identified as the predominant strain circulating both in outbreak and sporadic cases. The results showed that norovirus was rather the important agent than other enteric viruses affected adults with acute gastroenteritis; no significant genetic relatedness of the dominant strains was found between the outbreak and sporadic cases.

Site-directed mutagenesis (SDM) has been a very important method to probe the function-structure relationship of proteins. In this study, we introduced an easy-to-use, polymerase chain reaction (PCR)-based SDM method for double-stranded plasmid DNA, with a designed restriction site to ensure simple and efficient mutant screening. The DNA sequence to be mutated was first translated into amino acid sequence and then the amino acid sequence was reversely translated into DNA sequence with degenerate codons, resulting in a large number of sequences with silent mutations, which contained various restriction endonuclease (RE) sites. Certain mutated sequence with an appropriate RE site was selected as the target DNA sequence for designing a pair of mutation primers to amplify the full-length plasmid via inverse PCR. The amplified product was 5′-phosphorylated, circularized, and transformed into an Escherichia coli host. The transformants were screened by digesting with the designed RE. This protocol uses only one pair of primers and only one PCR is conducted, without the need for hybridization with hazardous isotope for mutant screening or subcloning step.