Demographic characteristics of overseas imported COVID-19 cases
From 29 February to 20 March 2020, 71 imported COVID-19 cases (2.79%) were identified from 2545 overseas travellers screened at emergency department of infectious diseases, Beijing Ditan Hospital, Capital Medical University. The demographic characteristics of the cases are described in Table 1. There were 27(38.03%) males and 44(61.97%) females. The median age of the cases was 24 years (IQR, 20-39; range, 6-55 years). A total of 11 clusters occurred, involving 39.44% of all COVID-19 cases. The cases were mainly acquired from Europe (63 cases, 88.73%). Of these, 22 (30.99%) cases were from Spain, followed by 17 (23.94%) cases from the United Kingdom and 16(22.54%) cases from Italy, respectively. The period from 29 February to 10 March 2020 was characterized by low numbers of imported cases. From 11 March onward, there was a gradual increase in the number of imported cases, of which the majority were 14 per day (Figure 2).
Clinical characteristics of overseas imported COVID-19 cases
The most common clinical manifestations at onset of illness were fever and cough, which accounted for 30 cases (42.25%) and 35 cases (49.30%), respectively. 15 (21.13%) cases had sore throat. In addition, 14 (19.72%) cases had fatigue, 9 (12.68%) cases had headache, 7 (9.86%) cases had myalgia or arthragia, 5(7.04%) cases had shortness of breath, 2(2.82%) cases had nausea or vomiting and 1(1.41%) cases had diarrhea. The median time from illness onset to hospital admission was 4.0 days (IQR, 2-7; range, 11 hours to 13 days).
According to laboratory findings at initial presentation, the white blood cell (WBC) count of 7 (9.90%) cases was lower than the normal range (4×109/L), and 4 cases (5.63%) had lymphocytopenia (the lymphocyte count was less than 1.0×109/L). 8(11.27%) cases had platelets higher than the normal range (300×109/L), and no case had lower platelets than the normal range (100×109/L). There were 13 (18.31%) cases with high CRP. There was a normal PCT value.
According to chest imaging findings at initial presentation, of 71 imported cases, 35 (49.30%) cases showed abnormal chest CT images, consisting 19 cases (26.76%) of bilateral pneumonia and 16 cases (22.54%) of unilateral pneumonia (Table 2),with typical findings of patchy ground-glass opacity(GGO) in lungs(Figure 3 A, B). There were 6(8.45%) cases of unilateral patchy consolidation and 5(7.04%) cases of bilateral consolidation in lungs (Figure 3 C, D). 36(50.70%) cases had no abnormality in the parenchyma of both lungs.
During the diagnostic procedure, we found that 59 cases (83.10%) got a positive result in the first RT-PCR test at initial presentation. However, the remaining 12 cases(16.9%) were further confirmed after admitting to the isolation ward. 5 cases (7.04%) got a positive result in the second RT-PCR test. 7 cases (9.86%) didn’t obtained positive results until 3-5 round of tests later (Figure 4).
The effectiveness of screening strategy
From 29 February to 20 March 2020, with the combination of screening tools, particularly CT and RT-PCR, 2.79% (71/2545) of entry screening cases were detected and isolated in time. However, those who were excluded from COVID-19 were tested for SARS-CoV-2 again after 14 days of isolation and all results were negative with telephone follow-up. At the same time, the local Centers for Disease Control and Prevention (CDC) had not reported any new confirmed cases in this population.