Norovirus diarrhea is a great threat to public health worldwide. To characterize the prevalence of circulating noroviruses associated with sporadic gastroenteritis cases in Guangzhou, 215 stool specimens were collected during two consecutive cold seasons in 2013-2015. Noroviruses were detected in 25 (11.63 %) samples, and GII.4 (6/9) and GII.17 (10/16) were identified as the most predominant variants of each of those seasons. The remaining strains belonged to the genotypes GII.P12/GII.3, GII.2, and GI.Pb/GI.6. The phylogenetic relationships of the GII.17 strains were analyzed based on their capsid protein sequences. This study suggests a significant shift of predominant variants associated with sporadic gastroenteritis in Guangzhou.

Background Human norovirus is regarded as the leading cause of nonbacterial acute diarrhea in developing and developed countries. Among all genotypes, GII.4 has been the predominant genotype, but in East Asia, it was replaced by the GII.17 in 2014/2015. However, after the prevalence of new GII.17 variant in South China, a sharply increase in the number of norovirus infections associated with sporadic acute diarrhea was detected. In this study, we would investigate the prevalence and genetic diversity of noroviruses in the sporadic acute gastroenteritis cases in the post-GII.17 period in South China. Methods Norovirus was screened from 217 patients with sporadic acute gastroenteritis from August 2015 to October 2017 by reverse transcription-polymerase chain reaction. Then, two regions including the partial RNA polymerase and the capsid gene of positive samples were amplified and sequenced. Phylogenetic analyses were performed to determine norovirus genotypes. Complete VP1 sequences of GII.4 strains detected in this study were also amplified and subjected into evolutionary tracing analyses. Results A total of 43 (19.82%) norovirus samples were confirmed from 217 stool specimens, and it was found that GII.4 resurged as the new predominant variant, accounting for 76.74% (33/43) of positive samples. Only one local strain GZ2015-L550 was clustered with the contemporary GII.P16/GII.4–2012 recombinant variant, and other 32 local strains belonged to the clade with the GII.Pe/GII.4–2012 variant. Other genotypes including GII.17 ( n = 4), GII.3 ( n = 4), GII.8 ( n = 1) and GI. 6 (n = 1) were also detected. Furthermore, all GII.4 strains were phylogenetic analyzed based on their capsid P2 subdomains. Combined with other reported 754 strains, the GII.4–2012 variant could be divided into two clades. Most GII.4 strains collected in 2016 and 2017 in this study (7/8) formed a new cluster A in Clade II with additional 103 contemporaneous strains. In addition, evolutionary tracing of the capsid P2 subdomain of this variant was also analyzed, and one specific amino acid substitutions (N373) was identified for Cluster A. Conclusion In summary, this study confirmed a norovirus infection peak in the post-GII.17 period in South China, which was caused by the resurgence of the GII.4 variant. Electronic supplementary material The online version of this article (10.1186/s12879-019-4331-6) contains supplementary material, which is available to authorized users.

Noroviruses are regarded as the major causes of acute gastroenteritis worldwide, but their prevalence in sporadic diarrhea in South China remains unclear. This study was performed to characterize the genotypes of circulating norovirus strains associated with sporadic diarrhea cases in Guangzhou from November 2010 to January 2011. Among fecal specimens collected from 89 patients with acute diarrhea, nine samples (10.11%) were norovirus positive and 32 samples (35.96%) were rotavirus positive. The partial polymerase and the capsid regions of these norovirus samples were sequenced and phylogenetically analyzed. Three genotypes (GII.4, GII.6, and GII.b/GII.3) were identified, among which GII.4-2006b was the most predominant genotype (4/9, 44.4%), followed by GII.6 (3/9, 33.3%). A novel GII.4-2010 variant was first detected in China. Furthermore, the near full-length genome of the GZ2010-L26 strain, which belonged to GII.4-2006b, was sequenced and analyzed. Thus, the results of this study suggested that, second to rotavirus, noroviruses are the important pathogens responsible for sporadic acute gastroenteritis during winter in Guangzhou, and the GII.4-2006b variant remains the predominant genotype.

Human sapovirus (SaV) is an important viral agent for acute diarrhea worldwide, but timely prevalence data of human SaV in South China are still lacking. In this study, a 4‐year surveillance was conducted to characterize the prevalence and genetic characteristics of the circulating SaV associated with sporadic diarrhea in South China. From November 2013 to October 2017, 569 fecal samples from patients with acute diarrhea were collected. SaV was detected in 11 samples with a positive rate of 1.93%. Three human genogroups of GI, GII, and GIV were identified, including five GI.1 strains, three GI.2 strains, one GI.3 strain, one GII.8 strain, and one GIV strain. Furthermore, multiple alignments of complete capsid protein VP1 genes of five local GI.1 strains and other available GI.1 strains in GenBank were performed. Average pairwise identities were calculated at 95.33% and 99.36% at nucleotide and amino acid levels, and only six variable amino acid sites were found during its 36‐years’ evolution process. GI.1 strains could be further phylogenetically divided into four clusters with an approximate temporal evolution pattern, and local strains belonged to Cluster‐d with other four strains from China and Japan. In summary, SaV was identified as an etiological agent responsible for sporadic gastroenteritis in Guangzhou with a low prevalence rate as in other Chinese cities, but its high genetic diversity suggested the necessity of continuous SaV surveillance in the future.

In order to verify that a high-power marine gas turbine engine can be redesigned to be a reversible one, concept verification was done on a reversible turbine test rig. The reversible power turbine test pieces were designed, which are transformed to be capable of rotating reversely. And more than 100 times of operational tests were done for the switching devices. Based on the reversible turbine test rig, 50 times of switching tests between normal and reverse rotational direction were done by compressed air under low temperature condition. While more than 100 times of operational tests were done with hot gas at temperature of 400–500 °C. The tests results show that the switching devices could operate flexibly and the output power reached over 40% of rated power condition. During the switching tests between the normal and reverse rotational direction, the propeller could stop running. All of these verify the concept feasibility of reversible gas turbine engine. Based on this concept, preliminary design was completed for a high-power marine gas turbine engine redesigned into a reverse one, which laid solid foundation for the following detailed design, experimental verification and application.