Epidemiological information and sample collection. The epidemiological data was retrieved from the China Information System For Disease Control And Prevention and the population data came from the Taiyuan Statistical Yearbook. A total of 2,701 throat swab specimens were sent to the virus microbiology laboratory of Taiyuan Center for Disease Control and Prevention (Taiyuan CDC) for enterovirus nucleic acid testing within 24h from January 1, 2016 to December 31, 2020. Upon receipt of specimens by laboratory, each specimen was assigned a unique laboratory code and entered into the Gastrointestinal Information Database of Taiyuan CDC (Excel).
RNA extraction and EV identification. Viral RNA was extracted from the throat swab specimens using a MagMAXTM-96 Viral RNA Isolation Kit (Thermo Fisher Scientific, Foster City, CA) according to the manufacturer′s instructions. RNA was eluted in a final volume of 50µL of elution buffer and used immediately or stored at-80℃. All steps of specimen preparation and RNA extraction were done in the biosafety cabinet. RNA was detected using a three-channel real-time RT-PCR kits (Diagnostic Kit for pan-EV, EV-A71, CVA16, Shanghai ZJ Bio-Tech Co., Ltd, Shanghai, China). A 25 µL reaction system consisting of 1 µL enzyme mixture,19 µL reaction solution, and 5 µL viral nucleic acid was prepared. PCR cycling parameters were set up as per the manufacturer’s protocols: 50°C for 30 min, 95°C for 10 min, followed by 45 cycles of 95°C for 10 s, and 55°C for 40 s in a CFX96 Real-time Thermal Cycler (Bio-Rad, Hercules, CA, USA). A positive result was defined as a cycle threshold (Ct) value ≤ 43, and the positive control was defined as a Ct value ≤ 35. The negative specimens were not under the scope of our study. The specimens positive for other EVs were detected using commercially available real-time RT-PCR kits ( Nucleic Acid Detection Kit for CVA10, BioMax Biotechnology Co., Ltd, Beijing, China). A 20 µL reaction system consisting of 5 µL primer probe mixture, 5 µL RT-PCR reaction solution (containing enzymes), and 10 µL viral nucleic acid was prepared. PCR cycling parameters were set up according to the instructions: 25°C for 2 min, 53°C for 10 min, 95°C for 2 min, followed by 45 cycles of 95°C for 5 s, and 60°C for 30 s in a CFX96 Real-time Thermal Cycler (Bio-Rad, Hercules, CA, USA). A positive result was defined as a Ct value ≤ 37, and the positive control was defined as a Ct value ≤ 32. The negative specimens were not under the scope of our study.
VP1 region amplification and nucleotide sequencing. In total, 31 specimens were detected to amplify the entire VP1 region of CVA10 by using the One Step RT-PCR kits (CVA10 Target region (VP1) Molecular typing Kit, BioMax Biotechnology Co., Ltd, Beijing, China) with specific in-house primer pairs (forward primer with nucleotide position 2172-2192nt, CVA10-VP1-S: GCTCAGTAACACTCAYTTYCG, and reverse primer with nucleotide position 3376-3394nt, CVA10-VP1-A: CTCGAGAACTGTCYTCCCA). The primers yielded a CVA10 amplification product of 1223 bp, spanning the entire VP1 region of CVA10 (894 bp). The reaction system for each tube consisted of 12.5 µL PCR Buffer, 2 µL PCR Enzyme, 0.5 µL RT Enzyme, 3µL Primer Mix, and 7 µL viral nucleic acid up to a final volume of 25 µl. The amplification conditions were as follows: 45°C for 10 min, 94°C for 2 min, followed by 45 cycles of 98°C for 10 s, 55°C for 15 s, and 68°C for 20 s in a ABI ProFlex™ 96-Well PCR System (Thermo Fisher Scientific, Foster City, CA). Amplification products were determined using 1% agarose gel electrophoresis image analysis system, and sent to Tsingke (Beijing) Biotechnology Co., Ltd for DNA bi-directional sequencing.
Phylogenetic analyses. Sequences were spliced by Sequencher software (version 5.4.6), and EV-types were verified by enterovirus automated genotyping tool [23]. Phylogenetic trees were constructed based on the VP1 sequences of the CVA10 identified in this study and the sequences downloaded from the GenBank database using the MEGA software (Version 11.0.11) [24]. Phylogenetic analysis using neighbor joining (NJ) method was performed based on the Kimura 2-parameter model, and the reliability was evaluated by 1000 bootstrap replicates. Bootstrap values greater than 80% were considered statistically significant for grouping. Genotype differences were computed by the group mean distance computing method in MEGA software.
Nucleotide Accession Number. All the CVA10-Taiyuan sequences obtained during this study were submitted in GenBank under accession numbers OP244619 - OP244649, which are shown in supplementary Table S1.
Statistical analyses. Data analyses were performed using IBM SPSS Statistics software (Version 26.0). The Pearson's Chi-Square Test was used to analyze the data, and the value of P༜0.05 was considered statistically significant.