COVID–19 is a new disease with high infectivity caused an enormous impact on public health . The Spring Festival travel rush has triggered massive population movements which gave rise to the confirmed cases of COVID–19 outside Wuhan with a history of exposure to Wuhan, as well as second-generation cases infected by the former or by individuals from Wuhan emerged across China in succession. In order to better master the characteristics of COVID–19 in patients outside Wuhan city for appropriate treatment, we carried out our study to investigate the discrepancy in CT manifestations of this pneumonia in patients outside Wuhan between cases with a history of exposure to Wuhan and the second-generation infection.
Our study revealed that abnormal findings on initial CT scans can be found in each patient outside Wuhan with a history of exposure to Wuhan but cannot in each patient with the second-generation infection. In patients with the second-generation infection, some patients could have abnormal initial CT appearances, and some could not. Our findings can be explained by the following pathological mechanism. As reported [15–17], RNA virus is characterized by error-prone viral replication and recombination and usually generates progeny viruses with highly diverse genomes which might result in reduction of virulence and pathogenicity. We could presume that the 2019-nCoV as a novel RNA virus might have the similar characteristics of reduction of virulence and pathogenicity resulted from the error-prone viral replication and recombination.
As shown in our study, GGO and consolidation could be the most common patterns of CT abnormalities of the confirmed COVID–19 in patients outside Wuhan, which was consistent with the published reports [9–11]. As reported , GGO and consolidation could respectively reflect the potential pathological abnormalities in different stages of the disease. Seen mainly in the early stage of the disease, the underlying pathologic change of pure GGO can be small amount of exudation of fluid in alveolar cavity and interlobular interstitial edema . Consolidation lesions could be regarded as a marker of more severe phase , reflecting a large amount of cell-rich or fibrous exudation accumulated in the alveolar cavity and pulmonary interstitium . It is noteworthy that 3 cases of second-generation with normal finding on initial CT scan developed into focal GGOs during follow-up CT, suggesting that the limitation of CT in the early detection of asymptomatic patients with the second-generation. The COVID case without abnormal manifestation on initial CT scan should be confirmed by 2019-nCoV detection via RT-PCR together with a history of close contact with the infected individuals exposed to Wuhan recently.
Moreover, we found that the discrepancies of extent and density scores obtained on the initial CT could exist between patients with a history of exposure to Wuhan and with the second-generation infection. In detail, the extent of lung lobe involved by COVID–19 lesions in patients with an exposure history of Wuhan was strikingly greater than that in patients with second-generation infection. The previous discrepancies of extent and density scores between groups can be explained as follows. In patients with a history of exposure to Wuhan, GGOs with consolidation or other abnormalities (i.e., reticular and/or interlobular septal thickening) involving multiple lobes could be more common than in patients with the second-generation infection, resulting in elevated CT density and extent scores in group A when compared with group B. Our findings suggest that patients with a history of exposure to Wuhan might have more rapid progression of disease and increasing likelihood of mixed bacterial coinfection [18–19]. Based on the comparison of CT density score between groups, we can presume that the COVID–19 in second-generation infected patients could be milder when compared to those with a history of exposure to Wuhan.
Our study had several limitations. For one thing, a larger sample size of COVID–19 patients is required for further investigation, especially with an emphasis on asymptomatic second-generation patients. For another thing, the semi-quantitative scoring system of disease in this study was based on the typical CT manifestations applied in the expert consensus , the other abnormal findings such as reticulation and interlobular septal thickening did not particularly evaluated, and further modification is required.
In conclusion, the CT findings of COVID–19 vary according to the routes of infection. Patients with a history of exposure to Wuhan tend to have more severe CT manifestations, suggesting that CT could accurately evaluate the COVID–19 in the population. Cases with second-generation infection could be manifested as normal finding on the initial CT scan, but may progress to mild abnormalities on follow-up CT, indicating 2019-nCoV detection via RT-PCR could be essential in the population with high risk of infection. We hope that our findings can help clinicians outside Wuhan formulate more accurate and effective prevention and treatment measures.