In China, when there are no more new local cases reported, imported cases have become a major challenge. In this study, 71 overseas imported COVID-19 cases in Beijing were reported. Our results demonstrated the effectiveness of combined screening tools to detect overseas imported COVID-19 cases.
Focusing on the period from 29 February to 20 March 2020, there was a consistent increase in the number of imported COVID-19 cases from overseas in Beijing, China. Cases from various regions demonstrated import situation at different points in time, with strong correlations to the epidemic situation in case exporting countries. Therefore, more attention should be paid on returnees from the high-burden areas according to the dynamic development of outbreak of COVID-19 in different countries. The first imported case seen in Beijing was from Iran on 29 February 2020, corresponding to the severity of the COVID 19 outbreak occurred in Iran at the same time. However, over the course of the next few days, the case exporting regions diversified, and cases from around the world were identified. This demonstrated the global spread of the disease along with the development of the pandemic. This also suggests that dynamic epidemiological history is of paramount importance for alert and early detection of COVID-19 patients.
All imported cases were screened first at the customs via temperature monitoring and self-health declaration and then transferred to emergency department of infectious diseases in Beijing Ditan Hospital. In this study, the most common symptoms were fever and cough, similar to the cohorts reported in current available literatures [11–13]. Only 2 cases were asymptomatic, but SARS-CoV-2 nucleic acid was positive. Fever is less frequent in those infected with SARS-CoV-2 than those with SARS-CoV (99%) and MERS-CoV (98%)[14]. Furthermore, asymptomatic carriers are potential sources of SARS-CoV-2 transmission and cannot be ignored [15, 16]. As screening heavily on syndromic detection, a substantial proportion of asymptomatic cases may be missed.
Previous studies have shown that chest CT scan is of great significance to screen the suspected cases of COVID-19[17]. In the early stage, there were ground-glass opacification with or without consolidative abnormalities, especially showed with a peripheral distribution. In severe cases, lung consolidation may occur, but pleural effusion was rare [18]. In our study, nearly half of imported cases showed abnormal chest CT images, with GGO and consolidation. This was consistent with the study by Huang et al [19].Therefore, in clinical practice, when SARS-CoV-2 nucleic acid is negative or the result cannot be returned in time, chest CT images can be used as an important alert and help to quarantine the patient at the very first time. Notably, normal chest CT imaging was found in 36(50.70%) cases compared to 17% of a recently study by Pan et al [20]. Therefore, a normal result from the initial CT scan does not rule out COVID-19 completely. The imaging features of COVID-19 were diverse and depended on the stage of infection after the onset of symptoms. A retrospective analysis of chest CT in 121 patients with COVID-19 by Bernheim et al[21] showed more frequent normal CT findings (56%) in the early stages of the disease (0–2 days). In this regard, we suggest that follow-up CT scan should be performed with an interval of 3 days to show the pulmonary dynamic changes.
In this study, all cases received SARS-CoV-2 test at initial presentation. The sum of nucleic acid test prior to a positive diagnosis for each patient was analyzed. However, 7 cases didn’t obtained positive results until 3–5 rounds of testing later. These negatives could result from improper sampling techniques or low viral load in the area sampled [22, 23]. Therefore, for patients with high clinical suspicion, specimens should be continuously collected for multiple tests to avoid missed diagnosis.
There are several limitations to our study. First, due to the limited number of patients, our conclusions need to be further verified by large samples and multi-center data. Secondly, due to time constraints, those who were excluded from COVID-19 at initial presentation had not been followed up for longer periods of time. Therefore, continued attention needs to be paid to the report of local CDC on COVID-19 outbreaks for further verification.