CEPVol. 63, No. 4, 119–124, 2020Review articleA cluster of severe pneumonia of unknown etiology in Wuhan City, Hubei province in China emerged in December 2019. A novel coronavirus named severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) was isolated from lower respi-ratory tract sample as the causative agent. The current outbreak of infections with SARS-CoV-2 is termed Coronavirus Disease 2019 (COVID-19) by the World Health Organization (WHO). COVID-19 rapidly spread into at least 114 countries and killed more than 4,000 people by March 11 2020. WHO officially declared COVID-19 a pandemic on March 11, 2020. There have been 2 novel coronavirus outbreaks in the past 2 decades. The outbreak of severe acute respiratory syndrome (SARS) in 2002–2003 caused by SARS-CoV had a case fatality rate of around 10% (8,098 confirmed cases and 774 deaths), while Middle East respiratory syndrome (MERS) caused by MERS-CoV killed 861 people out of a total 2,502 confirmed cases between 2012 and 2019. The purpose of this review is to summarize known-to-date information about SARS-CoV-2, transmission of SARS-CoV-2, and clinical features.Key words: SARS-CoV-2, COVID-19, Coronavirus, SARS-CoV, MERS-CoVIntroductionIn December 2019, a cluster of patients with pneumonia of unknown origin was identified in Wuhan, Hubei Province, China. Most patients witnessed a history of visiting Huanan Sea-food Wholesale Market. On December 31, 2019, the Chinese Center for Disease Control and Prevention (China CDC) and Wuhan City health authorities reported an outbreak of pneumonia of unknown causes in Wuhan City.1,2)On January 7, 2020, the China CDC identified a novel coronavirus from the lower respiratory tract samples of the patients with pneumonia and disclosed the genomic sequence on January 11.3,4)This novel coronavirus was later named severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). The World Health Organization (WHO) named this infection, caused by SARS-CoV-2 identified in 2019, Coronavirus Disease 2019 (COVID-19).5)Despite the effort to stop the transmission of COVID-19, the infection spread throughout mainland China, and in January 2020, cases were reported in Thailand, Japan, and South Korea.6,7)Within less than 3 months since the discovery of the unknown pathogen, the infection spread to at least 114 countries and caused more than 4,000 deaths. On March 11, the WHO announced COVID-19 outbreak a pandemic.8)In South Korea, the first case was identi-fied on January 20, 20207), and as of March 26, a total of 9,241 confirmed cases leading to 131 deaths (1.42% fatality rate) has been reported.9)Two novel strains of coronavirus have jumped species from animal to human, spread by human-to-human transmission, and caused severe acute respiratory syndrome leading to high fatality rate in the past 2 decades.10)Severe acute respiratory syndrome-associated virus (SARS-CoV), previously unknown coronavirus traced to horseshoe bats in southern China, caused 8,096 confirmed cases and 774 deaths (9.6% fatality rate) in 29 countries from November 2002 to July 2003.