Chest CT in patients with a moderate or high pretest probability of COVID-19 and negative swab
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CHEST RADIOLOGY
Chest CT in patients with a moderate or high pretest probability of COVID‑19 and negative swab Caterina Giannitto1 · Federica Mrakic Sposta1 · Alessandro Repici2,3 · Giulia Vatteroni1,4 · Elena Casiraghi5 · Erminia Casari6 · Giorgio Maria Ferraroli7 · Alessandro Fugazza2 · Maria Teresa Sandri6 · Arturo Chiti3,8 · Balzarini Luca1 Received: 4 June 2020 / Accepted: 16 August 2020 © Italian Society of Medical Radiology 2020
Abstract Objectives We aimed to assess the diagnostic performance of CT in patients with a negative first RT-PCR testing and to identify typical features of COVID-19 pneumonia that can guide diagnosis in this case. Methods Patients suspected of COVID-19 with a negative first RT-PCR testing were retrospectively revalued after undergoing CT. CT was reviewed by two radiologists and classified as suspected COVID-19 pneumonia, non-COVID-19 pneumonia or negative. The performance of both first RT-PCR result and CT was evaluated by using sensitivity (SE), specificity (SP), positive predictive value (PPV), negative predictive value (NPV) and area under the curve (AUC) and by using the second RT-PCR test as the reference standard. CT findings for confirmed COVID-19 positive or negative were compared by using the Pearson chi-squared test (P values 37·5 °C), cough, and dyspnea. A patient was considered as COVID-19 positive or negative after a positive or negative bronchoalveolar lavage or a second nasopharyngeal RT-PCR test. The preferred choice in our hospital was the RT-PCR test from bronchoalveolar lavage after a first negative RTPCR swab. We excluded patients who did not undergo CT examination or without two RT-PCR tests.
Laboratory data Nasopharyngeal swabs or bronchoalveolar lavage specimens were analyzed with RT-PCR technique to confirm the presence of the SARS-CoV-2 virus in the upper or lower respiratory tract. Two methods were used. One method is based on RNA extraction through high-affinity magnetic silica (Biomérieux, France) and amplification with AllplexTM 2019nCoV Assay (Seegene, Seoul, South Korea), a multiplex real-time PCR assay for simultaneous detection of 3 target genes of SARS-CoV-2 in a single tube with the CFX96TM real-time PCR instrument (Bio-Rad, France). The assay is designed to detect N, E and RdRP genes. The second system detected the same genes and was performed on the InGenius instrument (GeneFinder COVID-19 Plus RealAmp kit— ELITech Group, South Korea).
CT acquisition technique As per our hospital COVID-19 protocol, all chest CT acquisitions were obtained with the patients in the supine position during end-inspiration without contrast medium
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injection. Chest CT was performed on a Philips (Netherlands) Brilliance 64 CT scanner dedicated only to patients with suspected COVID-19. The following technical parameters were used: tube voltage 120 kV; tube current modulation 127 mAs; spiral pitch factor 1·490; rotation time 0·4 s, matrix 512; reconstructions had a slice thickness of 2 mm.
CT image analysis Two radiologists with five and f
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