Discussion
As of February 12th, 2020, 28 cases of COVID-19 have been reported in Korea, with the first case observed in a traveler residing in Wuhan, China. The SARS-CoV-2 was isolated from a Korean patient who had self-administered antipyretics for initial symptoms such as chills and fever. The patient had experienced intermittent coughing with sputum 3 days after the administration of antipyretics. The SARS-CoV-2 could replicate in other cells (Vero E6 and Caco-II cells), in addition to Vero cells (data not shown). The first SARS-CoV-2 was successfully isolated by inoculating human airway epithelial cells with bronchoalveolar-lavage fluid samples from a patient with pneumonia [16]. Since human airway epithelial cells (because of their resemblance to pseudostratified mucociliary epithelium) require 4–6 weeks to differentiate in vivo, isolation of SARS-CoV-2 using Vero cells or Caco-II cells is more convenient. Further studies are needed to select more sensitive cell lines suitable for virus isolation from low viral load samples.
The sequence of the suspected novel coronavirus (KCDC03) was analyzed using the sequences of 54 SARS-CoV-2 including 6 human coronaviruses, Bat-CoVs, and 51 SARS-CoV-2 that have been registered in GISAID by several countries including China, and a phylogenetic tree was produced. Results show that the isolate from Korea was clustered with the new coronavirus, SARS-CoV-2 and classified as betacoronavirus. High homology (99.94%–99.99%) was confirmed with the viral sequences reported from other countries, such as those from Wuhan/IVDC-HB-01/2019(GISAID accession ID: EPI_ISL_402119). Homology with bat CoV (bat-SL-CoVZC45), SARS-CoV (AY278741) and MERS-CoV (JX869059) was 89.1%, 77.5%, and 50%, respectively. However, the lowest homology of 99.5% was observed with BetaCoV/Wuwhan/IVDCHB-04/2020, which could be because of the inaccurate sequence of IVDCHB-04, Hence, it has been excluded from the comparative analysis in other studies.
Prior to identification of SARS-CoV-2 as the causative agent of the unknown pneumonia in Wuhan, China, pan-CoV RT-PCR was being used to detect SARS-CoV-2 in Korea. The Pan-CoV RT-PCR detects all human coronaviruses and animal-derived coronaviruses (personal communication). Since the release of the SARS-CoV-2 sequence, a real-time RT-PCR method has been established in the diagnosis of COVID-19 patients. Currently, the diagnosis of COVID-19 is based on gene detection via real-time RT-PCR. With the isolation of the causative agent, development of serological tests and rapid diagnostic tests in addition to virus detection will be required.