Epidemiological characteristics of imported cases of coronavirus disease 2019 in Chengdu, Sichuan

  Objective  To understand the epidemiological characteristics of imported coronavirus disease 2019 (COVID-19) cases detected in Chengdu, Sichuan, and provide scientific basis for the prevention and control of COVID-19.

  Methods  The data of imported COVID-19 cases in Chengdu were obtained from National Notifiable Disease Report System of China CDC, field epidemiological investigation reports by CDCs in Chengdu, and flight related information from Chengdu airport. Software Epidata Manager, WPS 2019 and R 4.0.3 were used for data management and statistical analysis. Descriptive statistics and χ² test were used to analyze the characteristics of the imported cases and inbound flights.

  Results  As of November 30, 2020, a total of 90 900 passengers from 36 countries and regions via 677 inbound flights (including 44 chartered airplane flights) had entered China at Chengdu Shuangliu International Airport. The passengers were mainly from Asia(63.98%, 58 154/90 900), but the attack rate in flights from Africa was relatively high ( χ²=133.137, P<0.001). Of the 677 flights, 136 flights had imported COVID-19 cases. The maximum of case number on one flight was 36, and the maximum daily case number was 25. The imported COVID-19 cases detected in Chengdu accounted for 6.88% of the total imported cases in China during the same period. Most cases had mild symptoms, and 162 (60.90%) were sub-clinical, most cases were diagnosed by chest CT. Up to 73.97% (324/438) of imported cases in Chengdu were diagnosed after the custom port preliminary quarantine screening, involving 38 clusters. The imported COVID-19 cases detected in Chengdu were mainly males (82.89%, 373/450), aged 20–50 years old (80.00%, 360/450) and workers (40.89%, 184/450). Most cases were not local residents.

  Conclusion  The imported cases of COVID-19 detected in Chengdu were mainly from countries or regions in Africa and Asia. Majority of the cases were sub-clinical, so strengthening the port case screening and close contact screening are essential to the prevention and control of COVID-19 in Chengdu, even in China.