Epidemiological investigation of an imported COVID-19 case infected with Delta variant from Nepal in Chongqing of China

  Objective  To analyze the epidemiological characteristics of a COVID-19 case imported from Nepal in Chongqing of China, and provide evidence for the prevention and control of imported COVID-19.

  Methods  Field epidemiological investigation was conducted for the case and the close contacts. Respiratory tract samples, such as throat swabs and nasopharyngeal swabs, were collected. Real-time fluorescent RT-PCR was used to detect the nucleic acid of SARS-CoV-2. The whole genome sequencing of SARS-CoV-2 was performed. Chemiluminescent fluorescence was used to detect the specific IgM and IgG antibodies to SARS-CoV-2.

  Results  The COVID-19 case imported from Nepal belonged to common type. The results of two SARS-CoV-2 nucleic acid tests and two IgM antibody tests of the cases were all negative within the 72 hours before returning to China, and the results of above tests of the case were all negative at airport customs after entering China. On the fifth day of centralized isolation, the test result of SARS-CoV-2 nucleic acid of the case was positive, and the gene sequencing found b.1.617.2 evolutionary clade of the Delta variant circulating in India recently. On the first day after admission to hospital, the case's IgM test result was negative and the IgG test result was positive.

  Conclusion  The Delta variant spread fast, the prevention of imported cases should be strengthened through precise and area specific measures. It is necessary to strengthen the personal protection in the closed-loop management process at air port, such as quarantine, transfer and isolation, and hospital infection control, medical observation and nucleic acid and antibody detections in the centralized isolation. Full doses of COVID-19 vaccination should be completed in time. At the same time, nasopharyngeal swab specimens should be collected form some travelers entering China.