Objective To analyze the epidemiological characteristic and tracing process of an outbreak of COVID-19 in a sea-land border city (D city) of Guangxi in December 2021, and provide scientific data for for the emergency management and scientific traceability of similar outbreaks in the future.
Methods Epidemiological investigation of cases was carried out under the guideline of the Novel Coronavirus Epidemiological Investigation Programme on Cases of Pneumonia (Edition 8). RT-PCR method was used for samples testing. Furthermore, positive samples were analyzed by whole-genome sequence and phylogenetic analysis. R software 4.1.3 version was used for data analysis.
Results There were 20 cases in this outbreak which related 6 families. The average incubation period was (4.6±2.2) d. Compared with the Wuhan reference strain (NC_045512), the genome sequence analysis showed that there were 35-36 nucleotide mutation sites in the novel Coronavirus genome sequence of 19 local cases, which belonged to VOC/Delta variant strain (AY.57 evolutionary branch). The 11 amino acid mutation sites were the same in all the novel Coronavirus spikes (S) proteins, which were highly homologous to the 2 COVID-19 genome sequences uploaded from a neighboring country in the GISAID genome database.
Conclusion This outbreak was caused by fishermen who were infected by contacting with persons of neighboring country in the public sea area and causing located community transmission. The management of border villagers and the monitoring of epidemic strains should be strengthened to detect and deal with the outbreak as early as possible in the future.
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