A 74-year-old woman with history of hypertension and heart disease, who had been discharged 10 days before knee prosthetic surgery, was admitted with 4-day history of fever, dry cough and dyspnoea. She had not left home since discharge and no family member was affected. Analysis revealed lymphopenia, elevation of C-reactive protein and a positive RT-PCR. The patient was admitted to the intensive care unit, with a favourable course.
Chest X-ray at admission showed diffuse reticular pattern with small opacities in both basal regions (Figure 1). Axial CT performed on first day showed diffuse ground glass opacity predominantly in the lower lobes with small peripheral consolidations in a posterior distribution (figures 2 and 3). Chest X-ray on the second day showed disease progression with diffuse reticular pattern and increased density in both lungs (figure 4) Chest x-ray on the eighth day showed improvement with decreased of high density and reticular pattern, more evident in the upper left lobe (figure 5).
Background The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS- CoV-2) disease in China at the end of 2019 (COVID 19) is a novel viral pandemic, that today affect to 693,282 and have caused death to 33,106 people around the world . Studies suggest zoonotic origin of the infection with subsequent human-human spread through droplets or direct contact [2-4]. Infection has mean incubation period of 6.4 days with a range of 0-24 days, and hospital-related transmission and asymptomatic carriers have been described [4-6]. The mean age of people affected in China was 47-49 years, 12-15% was elderly patients and male sex comprised more than half of the cases . Clinical Perspective Fever is the most common symptom described in many studies followed by dry cough and dyspnoea [4,6,7]. Most patients had a normal white blood cell count, but more than 50% had leukopenia [4,7,8] According to a summary report of many cases, 14% were severe (dyspneoa, tachypnea and blood oxygen saturation<93%) and 5% were critical (respiratory failure and shock septic) . These groups were more likely to have comorbidities (at least 20%), being hypertension the most common . The overall case-fatality rate was 2.3% and in elderly patients was 8-15%.  Imaging Perspective Chest radiographs are of little diagnostic value in early stages, whereas CT findings may be present even before symptom onset  and almost all patients with COVID 19 had characteristic CT features in disease process . More than half of patients presented bilateral multilobar ground-glass opacification (GGO) with a peripheral distribution [8,10] sometimes with a rounded morphology [ 11, 12]. CT in the intermediate stage shows and increase in the number and size of GGOs and transformation of GGO into multifocal consolidative opacities, septal thickening and development of a crazy paving pattern . Bronchiectasis, pleural thickening, subpleural involvement, pleural effusion, pericardial effusion, lymphadenopathy, cavitation, CT halo sign and pneumothorax are uncommon but Main Document 2 may be seen with disease progression . Pleural effusion and lymphadenopathy was considered of poor prognosis . Imaging patters corresponding to clinical improvement usually occur after week 2 of the disease . Outcome The reference standard in COVID-19 diagnosis is real-time reverse transcription polymerase chain reaction (RT-PCR) of viral nucleic acid that has low sensitivity, however, chest CT has high sensitivity for diagnosis in patients with initial false negative RT-PCR results [14,15, 16], so it can be considered a useful diagnostic tool and radiologists must know the typical findings of this disease. Teaching Points The presence of ground glass opacity and peripheral consolidations of bilateral distribution in the current clinical and epidemiological context is diagnosis of COVID-19.
 Zunyou Wu, Jennifer McGoogan. Characteristics of and Important Lessons From the Coronavirus Disease 2019 (COVID-19) Outbreak in China. Summary of a Report of 72.314 Cases From the Chinese Center for Disease Control and Prevention. Jama published online 24, 2020. (PMID: 32091533).
 Roujian Lu, Xiang Zhao, Juan Li, Peihua Niu, Bo Yang, Honglong Wu, Wenling Wang, Hao Song, Baoying Huang Na Zhu, Yuhai Bi, Xuejun Ma, Faxian Zhan, Liang Wan, Tao Hu, Hong Zhou, Zhenhong Hu, Weimin Zhou, Li Zhao, Jin Chen, Yao Meng, Ji Wang, Yang Lin, Jianying Yuan, Zhihao Xie, Jinmin Ma, William J Liu, Dayan Wang, Wenbo Xu, Edward C Holmes George F Gao, Guizhen Wu, Weijun Chen, Wifwn Shi, Wenjie Tan. Genomic Characterisation and Epidemiology of 2019 Novel Coronavirus: Implications for virus origins and receptor bindibg. The Lancet; 395 February 22 2020. (PMID: 32007145).
 Chih-Cheng Lai, Tzu-Ping Shih, Wen-Chien Ko, Hung-Jen Tang, Po-Ren Hsueh. Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and Coronavirus Diseae-2019 (COVID-19): The Epidemic and the Challenges. International Journal of Antimicrobial Agents 55(2020) 105924. (PMID: 32081636).
 Yan Bai, Lingsheng Yao, Tao Wei, Fei Tian, Dong-Yan Jin, Lijuan Chen, Meiyun Wang. Presumed Asymptomatic Carrier Transmission of COVID-19. Jama published online February 21, 2020. (PMID: 32083643).
 Chinh- Cheng Lai, Yen Hung Liu, Cheng-Yi Wang, Ya-Hui Wang, Shun-Chung Hsueh, Muh-Yen Yen, Wen-Chien Ko, Po-Ren Hsueh. Asymptomatic Carrier State, Acute Respiratory Disease, and Pneumonia Due to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2): Facts and Myths. Journal of microbiology, Inmunology and Infection, https://doi.org/10.1016/j.jmii.2020.02.012 (PMID: 32173241).
 Fengxiang Song, Nannan Shi, Fei Shan, Zhiyong Zhang, Jie Shen, Hongzhou Lu, Yu Ling, Yebin Jiang, Yuxin Shi. Emerging2019 Novel Coronavirus (2019-nCoV) Pneumonia. Radiology 2020; 295:210-217. (PMID: 32027573).
 Rui Han, Lu Huang, Hong Jiang, Jin Dong, Hongfen Peng, Dongyou Zhang. Early Clinical and CT Manifestations of Coronavirus Disease 2019 (COVID-19) Pneumonia. American Journal of Roentgenology 2020; 215:1-6. (PMID: 32181672)
 Sana Salehi, Aidin Abedi, Sudheer Balakrishnan, Ali Gholamrezanezhad. Coronavirus Disease 2019 (COVID-19): A systematic Review of Imaging Findings in 919 Patients. American Journal of Roentgenology 2020 Mar 14:1-7. doi: 10.2214/AJR.20.23034. (PMID: 32174129)
 Xi Xu, Chengcheng Yu, Jing Qu, Lieguang Zhang, Songfeng Jiang, Deyang Huang, Bihua Chen, Zhiping Zhang, Wanhua Guan, Zhouku Ling, Rui Jiang, Tianlu Hu, Yan Ding, Lin Lin, Qingxin gan, Liangpin Luo, Xiaoping Tang, Jinxin Liu. Imaging and Clinical Features of Patients with 2019 Novel Coronavirus SARS-CoV-2. European Journal of Nuclear Medicine and Molecular Imaging, published online: 28 February 2020. (PMID: 32107577).
 Michael chung, Adam Bernheim, Xueyan Mei, Xueyan Mei, Ning Zhang, Mingqian Huang, Xianjun Zeng, Jiufa Cui, Wenjian Xu, Yang Yang, Zahi Fayad, Adam Jacobi, Kunwei Li, Shaolin Li, Hong Shan. CT Imaging Features of 2019 Novel Coronavirus (2019-nCoV), Radiology, 2020; 295:202-207. (PMID: 32017661).
 Chun Shuang Guan, Zhi Bin Lv, Shuo Yan, Yan Ni Du, Hui Chen, Lian Gui Wei, Ru Ming Xie, Bu Dong Chen. Imaging Features of Coronavirus Disease 2019 (COVID-19): Evaluation on Thin-Section CT. Academic Radiology; 2020:--:1-5. Article in press. (PMID: 32204990).
 Zheng Ye, Yun Zhang, Yi Wang, ZixiNG Huang, Bin Song. Chest CT Manifestation of New Coronavirus Disease 2019 (COVID 19): A Pictorial Review. European Journal of Radiology. 2020, Publish online March 19. (PMID: 32193638).
 Tao AI, Zhenlu Yang, Hongyan Hou, Chenao Zhan, Chong Chen, Wenzhi Lv, Qian Tao, Ziyong Sun, Liming Xia. Correlation of Chest CT and RT-PCR Testing in Coronavirus Disease 2019 (COVID-19) in China: A Report of 1014 Cases. Radiology, published online Feb 26, 2020. (PMID: 32101510).
 Yicheng Fang, Huangqi Zhang, Jicheng Xie, Minjie Lin, Lingjun Ying, Peipei Pang, Wenbin Ji. Sensitivity of Chest CT for COVID-9: Comparison to RT-PCR. Radiology, published online Feb 19, 2020. (PMID: 32073353).
 Chunqin Long, Huaxiang Xu, Qinglin Shen, Xianghai Zhang, Bing Fan, Chuanhong Wang, Bingliang Zeng, Zicong Li, Xiaofen Li, Honglu Li. Diagnosis of the Coronavirus disease (COVID-19): rRT-PCR or CT? European Journal of Radiology 2020; published online March 25. (PMID: 32229322).