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Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has caused a worldwide pandemic. The first reports of patients with COVID-19 were provided to World Health Organization on December 21, 2019 and were presumably associated with seafood markets in Wuhan, China. As of October 25, 2020, more than 42 million cases have been confirmed worldwide, with more than 1.1 million deaths. Asymptomatic transmission contributes significantly to transmission, and clinical features are non-specific to the disease. Thus, the diagnosis of COVID-19 requires specific viral RNA testing. The disease demonstrates extensive human-to-human transmissibility and has infected healthcare workers at high rates. Clinical awareness of the epidemiology and the risk factors for nosocomial transmission of COVID-19 is essential to preventing infection. Moreover, effective control measures should be further identified by comprehensive evaluation of hospital and community responses. In this review, we provide a comprehensive update on the epidemiology, presentation, transmission, risk factors, and public health measures associated with COVID-19. We also review past insights from previous coronavirus epidemics [i.e., severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS)] to suggest measures to reduce transmission., Competing Interests: The authors have no potential conflicts of interest to disclose., (© Copyright: Yonsei University College of Medicine 2021.)

In December 2019, an acute respiratory disease caused by novel species of coronavirus (SARS-CoV-2), emerged in China and has spread throughout the world. On 11 th March 2020, the World Health Organization (WHO) officially declared coronavirus disease 19 (COVID-19) a pandemic, severe coronavirus-mediated human disease. Based on genomic and phylogenetic studies, SARS-CoV-2 might originate from bat coronaviruses and infects humans directly or through intermediate zoonotic hosts. However, the exact origin or the host intermediate remains unknown. Genetically, SARS-CoV-2 is similar to several existing coronaviruses, particularly SARS-CoV, but differs by silent and non-silent mutations. The virus uses different transmission routes and targets cells and tissues with angiotensin-converting enzyme 2 (ACE2) protein, which makes it contagious. COVID-19 shares both the main clinical features and excessive/dysregulated cell responses with the two previous Middle East respiratory syndrome coronavirus (MERS) and severe acute respiratory syndrome coronavirus (SARS) epidemics. In this review, we provide an update of the current knowledge on the COVID-19 pandemic. Gaining a deeper understanding of SARS-CoV-2 structure, transmission routes, and molecular responses, will assist in the prevention and control of COVID-19 outbreaks in the future., Competing Interests: Competing Interests: The authors have declared that no competing interest exists., (© The author(s).)