The main results of this meta-analysis are as follows: 1) the sensitivity of chest CT for COVID-19 was great in Wuhan, but varied among other regions; 2) few studies reported the specificity of chest CT which was about 25%.
Chest CT plays an important role in detection of COVID-19, especially in the initial and peak period of epidemic, in China. Although the RT-PCR assay remains the standard of reference, it has been reported that false negative after the initial test was not rare and shortage of laboratory kit in the early stage of the outbreak restricted the early detection of COVID-19. As our findings, chest CT had great sensitivity for early detecting COVID-19, especially in regions more affected by epidemic such as Wuhan. Therefore, a clinical diagnosis criteria based on typical CT imaging features was temporarily adopted in the Guideline of Diagnosis and Treatment, which was only applicable in Hubei Province, China.3 This move allowed to early detect a large number of clinical diagnoses of COVID-19 under the background of shortage of RT-PCR assay which contributed to effective control of epidemic situation in China. Nevertheless, as mentioned above, among regions other than Wuhan, the reported sensitivity of chest CT varied and generally lower than that in Wuhan. Several reasons might underlie this phenomena, such as heterogeneity of experience of radiologists, severity of illness and epidemic. However, unfortunately, most studies did not provide relative informations. Wu Jian et al. reported a relative low sensitivity of chest CT (69%) and in their study the proportion of severe patients was only about 3.8% far less than the average level of China which was about 15%.6, 11 Moreover, Harrison et al. investigated the performance of radiologists in reading chest CT images of COVID-19 which found the experience of radiologists had a great impact on the diagnosis accuracy of chest CT.15 Overall, chest CT has a great sensitivity for detecting COVID-19, especially in regions with severe epidemic situation, and was helpful to early detect suspicious cases, which was vital to control epidemic.
In contrast to the great sensitivity of chest CT, the specificity was relative low with reporting about 25%. The typical chest CT findings of COVID-19 included ground-glass opacities
(GGOs), consolidations and interlobular thickening, which were usually multifocal and involved bilateral lungs.16 In mild patients or early period of COVID-19, chest CT could be negative or pure GGO lesions. The CT imaging features might overlap between COVID-19 and other viral pneumonia, which could reduce the specificity of chest COVID-19. Nevertheless, considering the rapidly spreading epidemic of COVID-19, it was priority to identify any suspicious case in order to isolate the patients and avoid cross infection. Therefore, In the context of emergency disease control, sensitivity was more important than specificity. On the other hand, as mentioned above, although RT-PCR was still regarded as standard reference, false negative results were not rare. Actually, in the study reporting specificity of chest CT, the results of RT-PCR turned from negative to positive in 15 patients and of these patients, 14 patients had positive findings in the initial chest CT.5
In addition to detection, chest CT also play an important role in management of COVID-19. As other pneumonias, the severity of COVID-19 is also positively related to chest CT findings. Intensive care unit (ICU) patients on admission often presented with bilateral multiple lobular and subsegmental consolidation, while non-ICU patients presented with bilateral GGOs and subsegmental consolidation. 17 Moreover, chest CT is helpful to surveil disease progression of COVID-19. Pan et al. investigated 21 confirmed patients and summarized four stages of COVID-19: early, progressive, peak, and absorption. 18 Growth of GGOs and expansion of consolidation are indicator of disease progression, and otherwise might indicate the improvement. 19-22
In conclusion, on the basis of limited and heterogeneous data, chest CT offers the great sensitivity for detecting COVID-19, especially in region with severe epidemic situation. The specificity is low. In the context of emergency disease control, chest CT provide a fast, convenient and effective method to early recognize suspicious cases, and contribute to reduction of cross infection.