Role of Ultra-Low Dose Chest CT and Chest Radiography for Coronavirus Disease 2019
The novel coronavirus-2 (SARS-CoV-2) infection with associated severe acute respiratory syndrome originated in China in December 2019 and reached the Lombardy region of northern Italy two months later. Ticino is the Swiss canton neighboring Lombardy in which the first Swiss cases were diagnosed on February 25th, 2020. On the 11th of March 2020, the World Health Organization (WHO) declared SARS-CoV-2 a pandemic. At the time of the writing of this article infection due to SARS-CoV-2 continue to increase worldwide. The most frequent symptoms of pneumonia caused by SARS-CoV-2 are fever and cough. Approximately 5% of infected patients are admitted to intensive care units . Significant increases in C-Reactive Protein (CRP) and Lactic Acid Dehydrogenase (LDH) as well as lymphocytopenia are present in most patients with SARS-CoV-2 and are considered negative prognostic indicators. Moreover, an increase of these biological parameters seems to correlate with the extension of infiltrates seen on chest CT scans.
The viral nucleic acid test, Reverse Transcription Polymerase Chain Reaction (RT-PCR) assay, has played a pivotal role in the diagnosis of SARS-CoV-2 and in clinical decision making regarding hospitalization and isolation of individual patients, however its lack of sensitivity, insufficient stability, and relatively long processing time have proven this test to be insufficient for timely characterization in the acute clinical setting and for the progression of the pandemic. The front-line radiological examination performed in these patients is usually a conventional chest radiograph, yet this modality has proven to be of limited value due to frequent false negative results.
By comparison, chest CT has proven to be more sensitive, with well documented features in patients with SARS-CoV-2 pneumonia, such as sub-pleural (peripheral), multifocal, bilateral ground glass opacities being commonly observed in more than half of patients. In the second phase of the disease, characteristic CT signs of lung damage such as crazypaving pattern or consolidations may appear. Several studies have demonstrated the evolution of chest CT findings of SARSCoV-2 pneumonia by classifying its radiological characteristics at different stages of infection. Specifically, in a retrospective study, chest CTs of 121 symptomatic patients infected with SARS-CoV-2 were reviewed and during the first two days of SARS-CoV-2 infection chest CT scans showed no infiltrates in half of the patients. Subsequently (between days 6-12), infiltrates appear in >90% of cases. Chest CT demonstrates a low false negative rate in the diagnosis of SARS-CoV-2 pneumonia and demonstrates the effectiveness of anti-inflammatory (inhaled interferon) or non-specific antiviral (lopinavir) therapies used in a later phase of the disease. Therefore, CT is a useful tool for diagnosis, management and therapeutic follow up of SARSCoV-2 pulmonary infections.
Nevertheless, medical radiation exposure remains an everimportant issue due to the broad range of the patient population effected by the pandemic, which includes all ages, as well as young individuals. New technologies and protocols such as ultra-low dose CT (uldCT) identify individual cases not seen on conventional radiography and can be implemented as a means of large-scale public health surveillance with reduced radiation exposures. Therefore, in epicenters of the pandemic, uldCT could be used as a screening tool or as an adjunct to RT-PCR to exclude occult infection, especially prior to surgery or intensive immunosuppressive therapies. The purpose of this study was to evaluate the utility of chest uldCT from initial diagnosis in the Emergency setting, compared to that of conventional chest radiographs in patients suspected for pneumonia with laboratory-confirmed SARS-CoV-2