A local COVID - 19 outbreak in Dalian caused by imported cold - chain products contaminated by SARS-CoV-2

ABSTRACT

On December 15, 2020, four dock workers tested positive for severe acute respiratory syndrome-coronavirus 2 (SARS-COV-2) nucleic acids and were reported by Dalian. Up until then, Dalian City had not reported local cases for 136 consecutive days. In this coronavirus disease 2019 (COVID-19) outbreak (referred to as the "Dalian COVID-19 outbreak"), samples from all infected persons (83) and part from the ship cargoes in contact With them during December 15, 2020 to January 8, 2021 were collected. Confirmed cases accounted for 61.45% (51/83) and asymptomatic infections accounted for 38.55% (32/83). Through high-throughput sequencing, 76 SARS-CoV-2 whole-genome sequences were obtained, of which 72 (86.75%) were from clinical samples, and 4 from cold-chain food packaging surface samples on cargo ship A of country R. Refer to Wuhan reference strain (NC_045512), genome analysis revealed 12-16 nucleotide mutations in 76 whole genomes sharing 12 nucleotide mutations and belong to the SARS-CoV-2 branch of B.1.1. Viral genomics and field epidemiological investigations showed that the Dalian COVID-19 outbreak was a local epidemic caused by dock workers infected with imported cold - chain products contaminated with SARS - CoV - 2. During transmission, 3 Virus generations and three relatively independent transmission chains were formed.