Identifying SNP threshold from P2 sequences for investigating norovirus transmission.

Noroviruses are a group of non-enveloped single-stranded positive-sense RNA virus belonging to Caliciviridae family. They can be transmitted by the fecal-oral route from contaminated food and water and cause mainly acute gastroenteritis. Outbreaks of norovirus infections could be difficult to detect and investigate. In this study, we developed a simple threshold detection approach based on variations of the P2 domain of the capsid protein. We obtained sequences from the norovirus hypervariable P2 region using Sanger sequencing, including 582 pairs of epidemiologically-related strains from 35 norovirus outbreaks and 6402 pairs of epidemiologically-unrelated strains during the four epidemic seasons. Genetic distances were calculated and a threshold was performed by adopting ROC (Receiver Operating Characteristic) curve which identified transmission clusters in all tested outbreaks with 80 % sensitivity. In average, nucleotide diversity between outbreaks was 67.5 times greater than the diversity within outbreaks. Simple and accurate thresholds for detecting norovirus transmissions of three genotypes obtained here streamlines molecular investigation of norovirus outbreaks, thus enabling rapid and efficient responses for the control of norovirus.

Mutations and Phylogenetic Analyses of SARS-CoV-2 Among Imported COVID-19 From Abroad in Nanjing, China.

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a pandemic and is threatening human health globally. The rapid genome sequencing and bioinformatic analysis of SARS-CoV-2 have become a helpful tool in the battle against the COVID-19. Here, we report the genetic characteristics, variations and phylogenetic analysis of SARS-CoV-2 sequenced from 42 clinical specimens. The complete genomes sequencing of SARS-CoV-2 were performed using Oxford Nanopore sequencing. All genomes accumulated mutations compared to the Wuhan-Hu-1 (GenBank Accession No: MN908947.3). Our data of the 42 whole genomes revealed 16 different lineages. The B.1.1 lineage was the most frequent, and 5, 2, 2, 3, and 1 sequences were classified as lineages of B.1.1.7, B.1.351, P.1, B.1.617.2, and C.37, respectively. A total of 328 nucleotide mutation sites were found in 42 genomes, among which A23403G mutation (D614G amino acid change in the spike protein) was the most common substitution. The phylogenetic trees of 42 SARS-CoV-2 sequences and GISAID-available SARS-CoV-2 sequences were constructed and its taxonomic status was supported. These results will provide scientific basis for tracing the source and prevention and control of SARS-CoV-2 imported from abroad in Nanjing, China.