Investigation of the first cluster of COVID-19 imported from the sea in Zhangzhou, China

Objective To analyze the first cluster of coronavirus disease 2019(COVID-19) imported from the sea in Zhangzhou, China in June 2022, and provide a reference for optimizing the epidemic prevention and control measures.

Methods Field epidemiological methods were used to investigate the activity trajectory of cases, identify and trace the close contacts, identify the sites involved in the epidemic, and conduct personnel and environmental sampling and testing.Positive samples were analyzed by gene sequencing.

Results On June 5, 2022, a truck driver engaged in seafood transportation was found to be positive for COVID-19 nucleic acid in the"All Those in Need Are Tested"work.The source of infection was traced to the contact with five Chinese mainland crew members during the loading process who were infected by trading with overseas personnel.A total of 13 cases of COVID-19 were determined in this outbreak, including 11 males and 2 females; the age ranged from 40 to 60 years, with an average age of 50 years; viruses were transmitted in three generations, with an average intergenerational transmission time of 3 d.The environmental samples of the truck, fishing boat, and truck driver's residence were positive for COVID-19 nucleic acid.Gene sequencing showed that the variant type in the 13 positive infected persons was Omicron variant (BA.2.3), which was highly homologous with that in the cases entering Xiamen from Taiwan, China during the same period.

Conclusion This outbreak is an imported cluster epidemic caused by crew members'contact with overseas personnel at sea, suggesting that the contact of crew members and fishermen with overseas ships and personnel at sea should be lessened during the COVID-19 epidemic, and nucleic acid screening and health management should be strictly implemented for personnel returning to the port to prevent and control the import of the epidemic from the sea.