The analysis of the characteristics of imported COVID-19 cases from January to April in 2020: a cross-sectional study.

Background: Since the first case reported in December 2019, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused an outbreak of coronavirus disease 2019 (COVID-19) worldwide. The global case count continued to rise and the WHO declared a Public Health Emergency of International Concern (PHEIC), causing a growing risk of imported COVID-19 infection. This study aimed to provide descriptive and quantitative epidemiological characteristics of imported COVID-19 cases in China.

Methods: This cross-sectional study examined all imported COVID-19 cases in Mainland China from 22 January to 21 April 2020. Ratios, Median and percentile were used for descriptive analysis. Spearman's correlation analysis was performed between daily new imported cases in Mainland China and the country of origin. The chi-square test was used to evaluate the difference between home quarantine and compulsory centralized quarantine on native transmission.

Results: A total of 1,610 cases of COVID-19 were imported from 49 countries to 27 provincial administrative regions in China; 79.8% were from European countries and the United States of America (the USA). Before 29 March 2020, the imported cases were mainly from the USA (27.7%) and United Kingdom (UK; 42.6%). After 29 March 2020, the daily newly imported cases from Russia rapidly grew. After 12 April 2020, the number of daily newly imported cases gradually decreased and remained at a low level (12±7 cases per day). Airport entry was encouraged, and ground border crossing was limited. Among the 1,610 cases, 54.0% were in the asymptomatic incubation period on arrival in Mainland China.

Conclusions: The transmissions by imported COVID-19 were gradually and effectively curbed in Mainland China, despite a disproportionally high number of cases worldwide. Entry screening measures must be implemented universally to all inbound travelers at a point of entry or targeted to specific travel routes or to specific travelers. Compulsory centralized quarantine should be recommended in the prevention of the imported COVID-19 epidemic.