Clinical and Radiological Features
COVID-19 has spread in more than 100 countries and regions around the world, raising grave global concerns. COVID-19 transmits mainly through respiratory droplets and close contacts, causing cluster infections. The symptoms are dominantly fever, fatigue, and dry cough, and can be complicated with tiredness, sore throat, and headache. A few patients have symptoms such as stuffy nose, runny nose, and diarrhea. The severe disease can progress rapidly into the acute respiratory distress syndrome (ARDS). Reverse transcription polymerase chain reaction (RT-PCR) and Next-generation sequencing (NGS) are the gold standard for diagnosing COVID-19. Chest imaging is used for cross validation. Chest CT is highly recommended as the preferred imaging diagnosis method for COVID-19 due to its high density and high spatial resolution. The common CT manifestation of COVID-19 includes multiple segmental ground glass opacities (GGOs) distributed dominantly in extrapulmonary/subpleural zones and along bronchovascular bundles with crazy paving sign and interlobular septal thickening and consolidation. Pleural effusion or mediastinal lymphadenopathy is rarely seen. In CT imaging, COVID-19 manifests differently in its various stages including the early stage, the progression (consolidation) stage, and the absorption stage. In its early stage, it manifests as scattered flaky GGOs in various sizes, dominated by peripheral pulmonary zone/subpleural distributions. In the progression state, GGOs increase in number and/or size, and lung consolidations may become visible. The main manifestation in the absorption stage is interstitial change of both lungs, such as fibrous cords and reticular opacities. Differentiation between COVID-19 pneumonia and other viral pneumonias are also analyzed. Thus, CT examination can help reduce false negatives of nucleic acid tests.
The literature has attributed the outbreak of the COVID-19 Pneumonia to a place called Huanan Seafood Market in Wuhan City, Hubei Province, China, so far, where live animals such as poultry, bats, marmots and other wild animals are sold, suggesting the possible transmission of pathogens from animals to humans. The present whole-genome phylogenetic analysis on 2019-nCoV shows that it has a much closer phylogenetic relationship to the SARS-like coronaviruses bat-SL-CoV ZC45 and bat-SL-CoV ZXC21 from Rhinolophus Sinicus (a species of Chinese Horseshoe Bat). Therefore, bats are considered the possible main host of 2019-nCoV. It has not been defined, however, whether 2019-nCoV pneumonia is transmitted through Rhinolophus Sinicus directly or via an intermediate host. Most scholars believe that Rhinolophus Sinicus is the most primitive host of the 2019-nCoV, and that the virus might be spread to humans through a yet unknown animal host, possibly pangolin. Recently, 149 mutational sites in 2019-nCoV have been detected, as suggested by the most recent Chinese research. The virus has evolved into two subtypes, L- and S-subtype, with the latter having stronger aggressiveness and infectiousness.
RNA, the hereditary substance of the virus, may become detectable post systemic infection of SARS-CoV-2. Nucleic acid detection aims to find RNA of SARS-CoV-2 in samples from the patient, so it is also the “Golden Standard” and an important approach in clinical diagnosis. There are mainly two methods in detecting nucleic acids of SARS-CoV-2, including NGS (Next-generation sequencing) and reverse transcription polymerase chain reaction (RT-PCR). NGS, the next generation of sequencing technology, was the first method that succeeded in detecting the new pathogen at the initial stage of the epidemic and defined soon the sequences of nucleic acids of SARS-CoV-2. The simplest and fastest strategy for detection will be undoubtedly the targeted fluorescence quantitative RT-PCR using primer probes designed for the conserved domains of the nucleic acid sequence that have been defined for the virus. This method involves a proliferation of specific RNA sequences in the sample post to their reverse transcription. Theoretically, the quantity of genome segments of the virus post to each amplification will be multiplied, and the visual detection will become feasible when segments of the targeted genes reach a certain number after more than 30 amplifications. Targets detected for nucleic acids of SARS-CoV-2 consist of three conserved sequences in the viral genome, including open reading frame 1ab (ORF1ab), nucleocapsid protein (N), and Envelope gene.
Journal of Clinical chemistry and Laboratory Medicne