Objective:To analyze the prevalence of human respiratory syncytial virus（RSV）and the evolutionary characteristics of the adhesion glycoprotein（G）gene in Xi'an from 2023 to 2024.Methods:Respiratory specimens were collected from patients with acute respiratory infections in Xi'an between October 2023 to October 2024. RSV nucleic acid screening was performed using real-time fluorescence quantitative PCR；full-length G gene sequencing was conducted on nucleic acid-positive specimens. Genotyping characterization of the obtained sequences was performed using Nextclade v3.10.0 software.Results:A total of 2 548 respiratory tract infection samples were collected，with 104 cases（4.08%，104/2 548）testing positive for RSV. The highest RSV positivity rate was observed in children aged ≤1 year（12.24%，18/147），and significant difference in positivity rates were found among age groups（χ 2=37.868， P<0.001）. Since October 2023，RSV has seen an epidemic peak during January to February 2024，and gradually declined thereafter，with no positive cases from May to September 2024. Among the 43 RSV-positive samples，12 strains were identified as subtype A（all genotype A.D.3），and 31 strains were subtype B（14 genotype B.D.4.1.1 and 17 genotype B.D.E.1）. Conclusion:From October 2023 to October 2024，RSV had an epidemic peak in January and February in Xi＇an，with subtype B being the predominant circulating type.

Objective:To investigate the epidemiological and genetic characteristics of hand, foot and mouth disease (HFMD) caused by coxsackievirus A6 (CVA6) in Xi′an city from 2021 to 2023.Methods:Collected clinical cases of HFMD, epidemiological information and samples were obtained. The specimens were tested by the real-time RT-PCR for enterovirus A71(EVA71), CVA16, CVA6 and CVA10, respectively. The VP1 regions of CVA6 were amplified and sequenced, MEGA X was used for phylogenetic analysis.Results:From 2021 to 2023, a total of 1 393 HFMD samples were collected, 1 106 (79.40%, 1 106/1 393) of which were positive for enteroviruses. The proportions of EVA71, CVA16, CVA6 and CVA10 were 0.45% (5/1 106), 16.64% (184/1 106), 72.42% (801/1 106) and 2.17% (24/1 106). A total of 801 HFMD cases tested positive for CAV6, including 783 mild cases and 18 severe cases, mainly in children aged ≤5 years (86.02%, 689/801), with a male/female ratio of 1.49∶1. The composition ratio of CVA6 infection differed with year(χ 2=332.62, P<0.01), and the highest composition ratio of CVA6 was in 2023 (91.01%, 638/701). The nucleotide and amino acid similarities in the VP1 region of Xi′an strains of CVA6 were 92.4%-99.8% and 98.3%-100.0%, respectively. Compared with the CVA6 prototype strain(Gdula), the nucleotide and amino acid similarities in the VP1 region of Xi′an strains were 82.2%-84.0% and 95.4%-96.0%, respectively, and there were 18 amino acid mutations in different degrees. Based on the phylogenetic analysis of VP1 region sequences, the CVA6 strains in Xi′an city from 2021 to 2023 belonged to D3a subtype, and could be divided into two clusters with 18 strains in cluster 1 while two strain in cluster 2. Conclusions:The sub-genotype D3a of CVA6 is the predominant virus causing HFMD in Xi′an city from 2021 to 2023, and there are two transmission chains. The monitoring and prevention of CVA6 should be strengthened.

Objective:To analyze the prevalence of human respiratory syncytial virus（RSV）and the evolutionary characteristics of the adhesion glycoprotein（G）gene in Xi'an from 2023 to 2024.Methods:Respiratory specimens were collected from patients with acute respiratory infections in Xi'an between October 2023 to October 2024. RSV nucleic acid screening was performed using real-time fluorescence quantitative PCR；full-length G gene sequencing was conducted on nucleic acid-positive specimens. Genotyping characterization of the obtained sequences was performed using Nextclade v3.10.0 software.Results:A total of 2 548 respiratory tract infection samples were collected，with 104 cases（4.08%，104/2 548）testing positive for RSV. The highest RSV positivity rate was observed in children aged ≤1 year（12.24%，18/147），and significant difference in positivity rates were found among age groups（χ 2=37.868， P<0.001）. Since October 2023，RSV has seen an epidemic peak during January to February 2024，and gradually declined thereafter，with no positive cases from May to September 2024. Among the 43 RSV-positive samples，12 strains were identified as subtype A（all genotype A.D.3），and 31 strains were subtype B（14 genotype B.D.4.1.1 and 17 genotype B.D.E.1）. Conclusion:From October 2023 to October 2024，RSV had an epidemic peak in January and February in Xi＇an，with subtype B being the predominant circulating type.

Objective:To investigate the epidemiological and genetic characteristics of hand, foot and mouth disease (HFMD) caused by coxsackievirus A6 (CVA6) in Xi′an city from 2021 to 2023.Methods:Collected clinical cases of HFMD, epidemiological information and samples were obtained. The specimens were tested by the real-time RT-PCR for enterovirus A71(EVA71), CVA16, CVA6 and CVA10, respectively. The VP1 regions of CVA6 were amplified and sequenced, MEGA X was used for phylogenetic analysis.Results:From 2021 to 2023, a total of 1 393 HFMD samples were collected, 1 106 (79.40%, 1 106/1 393) of which were positive for enteroviruses. The proportions of EVA71, CVA16, CVA6 and CVA10 were 0.45% (5/1 106), 16.64% (184/1 106), 72.42% (801/1 106) and 2.17% (24/1 106). A total of 801 HFMD cases tested positive for CAV6, including 783 mild cases and 18 severe cases, mainly in children aged ≤5 years (86.02%, 689/801), with a male/female ratio of 1.49∶1. The composition ratio of CVA6 infection differed with year(χ 2=332.62, P<0.01), and the highest composition ratio of CVA6 was in 2023 (91.01%, 638/701). The nucleotide and amino acid similarities in the VP1 region of Xi′an strains of CVA6 were 92.4%-99.8% and 98.3%-100.0%, respectively. Compared with the CVA6 prototype strain(Gdula), the nucleotide and amino acid similarities in the VP1 region of Xi′an strains were 82.2%-84.0% and 95.4%-96.0%, respectively, and there were 18 amino acid mutations in different degrees. Based on the phylogenetic analysis of VP1 region sequences, the CVA6 strains in Xi′an city from 2021 to 2023 belonged to D3a subtype, and could be divided into two clusters with 18 strains in cluster 1 while two strain in cluster 2. Conclusions:The sub-genotype D3a of CVA6 is the predominant virus causing HFMD in Xi′an city from 2021 to 2023, and there are two transmission chains. The monitoring and prevention of CVA6 should be strengthened.

Objective:To investigate the genetic and evolutionary characteristics of hemagglutinin (HA) and neuraminidase (NA) genes of influenza B/Victoria (BV) virus in Xi′an city from 2019 to 2023.Methods:Twenty-five BV strains isolated from the Xi′an influenza surveillance network laboratory between 2019 and 2023 were collected. The HA and NA genes were sequenced using MiniSeq high-throughput sequencing platform. An evolutionary tree was constructed using bioinformatics software to analyze homology and mutation sites, and to predict N-glycosylation sites online. The antigenicity of the strains was analyzed through hemagglutination inhibition tests.Results:The BV influenza in Xi′an exhibited a distinct seasonal transmission pattern from 2019 to 2023, with peak prevalence occurring during the winter and spring seasons. The evolutionary analysis of the HA genes shows that the strains from Xi′an in 2019 belong to the V1A.3 branch, and the strains from 2021 to 2023 belong to the V1A.3a.2 branch. Analysis of antigenic sites showed that there were variations in 6 sites of 3 antigenic determinants in the HA proteins of the BV strains from 2021-2022 compared to 2019, and 2 sites of 1 antigenic determinant changed in the HA proteins in 2023 compared to 2021-2022. The evolutionary analysis of the NA genes indicates that the BV strains from Xi′an in 2019 belong to the A. 1.1 branch. By 2021 and 2022, it had evolved into the A. 1.2 clade, and by 2023, it had further evolved into the B clade and its derivatives, with no strains showing mutations associated with resistance to NA inhibitors. Antigenic analysis indicated that the majority of BV strains in Xi′an were similar to the strains included in the vaccine composition. Furthermore, glycosylation analysis showed that the potential N-glycosylation sites in the HA proteins of BV strains from 2021-2023 were reduced by one compared to those from 2019, and only a few strains from 2023 displayed alterations in the potential N-glycosylation sites of the NA proteins.Conclusions:The HA and NA genes of the BV strains from 2019 to 2023 are continuously mutating and evolving into new branches. Since 2021, V1A.3a.2 has become the dominant evolutionary branch of the HA genes, while the evolutionary branches of the NA genes from 2019 to 2023 have been continuously changing.

Objective:To analyze the etiological and epidemiological characteristics of hand, foot and mouth disease (HFMD) in Xi′an from 2019 to 2021, so as to provide evidence for the prevention and control of HFMD.Methods:Stool specimens and anal swabs were collected from patients with HFMD. Enteroviruses (EVs) including enterovirus 71 (EV71), coxsackievirus A16 (CVA16), CVA6 and CVA10 were detected by RT-PCR. Excel 2007 and SPSS18.0 software were used for data collection and statistical analysis, respectively. The epidemiological data of HFMD cases were analyzed by descriptive epidemiology method. The VP1 gene sequence of the representative strain of each CVA6 genotype was downloaded. Phylogenetic trees were constructed using MEGA X software and the genetic characteristics were analyzed.Results:A total of 1 531 HFMD cases were involved and 1 365 were positive for EVs with a positive rate of 89.16%. The detection rates of EV71, CVA16, CVA6, CVA10 and other EVs were 1.31% (20/1 531), 32.46% (497/1 531), 38.47% (589/1 531), 5.09% (78/1 531) and 11.23% (172/1 531), respectively. There were significant differences in the pathogen composition in HFMD cases of different clinical types (χ 2=46.14, P<0.01) and occupations (χ 2=34.65, P<0.01) as well as in different years (χ 2=462.86, P<0.01). The average age was greater in patients with CVA16 infection than in those with CVA6 or CVA10 infection ( F=6.00, P<0.01). In 2019, the HFMD cases were mainly caused by CVA16, while in 2020 and 2021, the main pathogen was CVA6. Enterovirus-positive cases showed a bimodal distribution with the main peak from May to July and the secondary peak from September to November. CVA16 was the predominant pathogen in spring and summer, and CVA6 was the predominant pathogen in autumn. CVA6 was the dominant pathogen in eight districts and counties of Xi′an; CVA16 was the dominant pathogen in six districts and counties; CVA6 and CVA16 co-circulated in one district. The CVA6 isolates belonged to two evolutionary branches of D3a subtype. Conclusions:CVA6 and CVA16 were the prevalent pathogens of HFMD and CVA6 subtype D3a circulated in Xi′an from 2019 to 2021. The pathogen composition of HFMD cases showed obvious differences in population, time and regional distribution.

Objective:To characterize the epidemiology of hand, foot and mouth disease (HFMD) cases caused by coxsackievirus group A type 6 (CV-A6) in Xi’an from 2016 to 2020 and provide evidence for the prevention and control of HFMD.Methods:The enterovirus (EV) types were identified using real-time RT-PCR. The data of HFMD cases were collected from the National Notifiable Infectious Diseases Reporting System of China Center for Disease Control and Prevention. Descriptive epidemiological method were used to analyze the distributions and the data were statistically analyzed with Excel 2007 and SPSS 18.0.Results:In the 4 034 HFMD cases, 17.85% had enterovirus group A type 71 (EV-A71) infections, 23.92% had coxsackievirus group A type 16 (CV-A16) infections, and 47.79% had other EV infections. 2 571 HFMD cases were randomly selected, including 1 268 other EV positive cases. The detection rate of CV-A6 in HFMD cases was 34.73% (893/2 571), and the constituent ratio of CV-A6 in other EV positive cases was 70.43% (893/1 268). The cases mainly occurred in children aged≤5 years (95.18%), more boys were affected than girls (1.47∶1). HFMD caused by CV-A6 was concentrated in April to June. Compared with EV-A71 and CV-A16, the clinical classification had significant difference in CV-A6 group ( χ2=139.55, P<0.001), but the ratio of sex and age-group had no significant difference ( F=2.74, P=0.065; χ2=2.43, P=0.297). Conclusions:The predominant pathogen of HFMD in Xi’an from 2016 to 2020 were other EV, among which CV-A6 accounted for the highest proportion in other EV positive cases. It is necessary to strengthen the prevention and control of HFMD caused by CV-A6 and carry out the surveillance for various pathogens of HFMD.

Objective:To understand the composition of the pathogen spectrum of hand, foot and mouth disease(HFMD)in Xi′an from 2017 to 2018 and the genetic characteristics of enterovirus 71 (EV-A71).Methods:From 2017 to 2018, 1735 anal swab specimens from HFMD patients in Xi′an HFMD sentinel hospitals were collected, and qPCR was used to identify EV-A71, Coxsackie virus A 16 (CV-A16) and other enteroviruses. Selected EV-A71 strains were isolated, and VP1 region was amplified and sequenced, then phylogenetic tree and homologic comparison were conducted.Results:A total of 1 565 positive samples of enterovirus RNA were detected, positive rate was 90.20%(1565/1735), of which 24.79%(388/1 565)were positive for EV-A71, 21.85%(342/1 565)were positive for CV-A16, and 53.36%(835/1 565)were positive for other enterovirus. The main pathogen in 2017 was EV-A71(45.08%) and in 2018 was non-EV-A71-non-CV-A16 enteroviruses (73.38%), and the difference in pathogen composition was statistically significant ( χ2=370.57, P<0.001). HFMD caused by EV-A71 was concentrated in April to July, accounting for 73.97% (287/388) of the total cases. The homology analysis of the EV-A71 VP1 region showed that the 20 isolated EV-A71 strains belonged to the C4a subtype, with nucleotide and amino acid homology of 94.4%-96.1% and 99.4%-100% respectively, which were separated from those of the previous Xi′an City, the homology of EV-A71 obtained was above 91.5%. The result of the genetic evolution analysis of the EV-A71 VP1 region showed that the EV-A71 strain and the representative strain of the C4a subtype in Xi′an from 2008 to 2018 were in the same branch, forming multiple epidemic clusters, the variation degree of VP1 region increased with time. Conclusions:Non-EV-A71-non-CV-A16 enteroviruses were the main pathogens of HFMD in Xi′an from 2017 to 2018, and C4a subtype EV-A71 is still circulating in Xi′an. The monitoring of the pathogen spectrum and molecular epidemiology of HFMD should be strengthened to provide work for further effective prevention and treatment of HFMD.

Objective:To explore the positive rates of 2019-nCoV nucleic acid at different time of courses of COVID-19.Methods:Patients with confirmed COVID-19 were enrolled in this study. Nasal and throat swabs were collected from different courses of disease. Real-time RT-PCR was used to detect 2019-nCoV nucleic acid.Results:From January 23 to February 20, 2020, a total of 120 confirmed cases of COVID-19 were reported in Xi’an, and 85 cases(70.83%) were positive in first detection. The COVID-19 cases included consistently nucleic acid positive and intermittently nucleic acid positive patients. 2019-nCoV nucleic acid could be detected in incubation period, and the longest observed duration of nucleic acid positive in this study was 26 days. The positive rate of 2019-nCoV nucleic acid was up to 84.21% on the 6th day, and the positive rate decreased as time passed during the course of COVID-19. Three patients (2.86%) were tested positive for 2019-nCoV nucleic acid again in nasal and throat swabs after discharge.Conclusions:The positive rate of 2019-nCoV nucleic acid was higher in the early stage of disease. 2019-nCoV nucleic acid can be detected in incubation period, and virus shedding may last for a long period.

Objective:To investigate the positive rates of 2019-nCoV nucleic acid in different specimens from confirmed COVID-19 cases during hospitalization and after discharge.Methods:Patients with confirmed COVID-19 were enrolled from designated hospitals. Nasal swabs, throat swabs, and specimens of stool, urine and blood were collected during hospitalization. After the patients were discharged, nasal swabs, throat swabs and stool specimens were collected during follow-up. Real-time RT-PCR was used to detect 2019-nCoV nucleic acid.Results:This study involved 25 confirmed COVID-19 cases. During hospitalization, all patients tested positive in both nasal and throat swab 2019-nCoV nucleic acid tests, and nine of them (36.00%) were positive in stool specimen test. Urine and blood specimen test results were all negative. Nasal swabs, throat swabs and stool specimens were collected from each patient 7 d and 14 d after discharge. Two patients (8.00%) tested positive for 2019-nCoV nucleic acid again in nasal and throat swab tests on 7 d, while all stool specimen tests were negative. No 2019-nCoV nucleic acid was detected in nasal swabs, throat swabs or stool samples on 14 d.Conclusions:2019-nCoV nucleic acid was detected in stool samples of confirmed COVID-19 cases during hospitalization. Nasal and throat swab nucleic acid tests turned positive again in some patients after discharge.