In early December 2019 a patient was diagnosed with an unusual pneumonia in the city of Wuhan, China. By December 31 the World Health Organization (WHO) regional office in Beijing had received notification of a cluster of patients with pneumonia of unknown cause from the same city.1 Wuhan, the capital city of Hubei Province in central China, is the nation’s seventh largest city, with a population of 11 million people. Over the next few days, researchers at the Wuhan Institute of Virology performed metagenomics analysis using next-generation sequencing from a sample collected from a bronchoalveolar lavage and identified a novel coronavirus as the potential etiology. They called it novel coronavirus 2019 (nCoV-2019).2 The US Centers for Disease Control and Prevention (CDC) refers to it as 2019 novel coronavirus (2019-nCoV).3
As of February 4, 2020, more than 20 000 cases of 2019-nCoV have been reported, 98.9% of them in China, and the outbreak is linked to more than 400 deaths. As the epidemic is evolving and the situation is rapidly changing, up-to-date reliable information on the number of cases and recommendations on management of cases and preventive interventions can be found at various sites, including the webpage developed by the CDC.3 Currently the number of infections outside of China remains small (approximately 180), but cases have been detected in 26 countries, including 11 cases in the United States.
While it is unclear how many people are truly infected, a modeling study suggests that as of January 25, 2020, 75 815 individuals have been infected in Wuhan alone.4 The authors calculated the basic reproductive number (the number of cases one infected individual generates), R0, of this outbreak to be 2.68 (95% CI, 2.47-2.86) and that the epidemic is doubling every 6.4 days. Because of extensive travel between China and cities like Bangkok, Hong Kong, Singapore, Tokyo, and Taipei, these locations have identified the majority of cases outside of mainland China. As testing becomes more frequent, the true number of cases and the full spectrum of disease will become more clear. However, for now, it appears that compared with the other 2 zoonotic coronaviruses that occurred in the last 20 years (severe acute respiratory syndrome [SARS] in 2002 and Middle East respiratory syndrome [MERS] in 2012), 2019-nCoV seems to have greater infectivity (eg, a higher R0) and a lower case fatality rate.1
From genetic sequencing data, it appears that there was a single introduction into humans followed by human-to-human spread. This novel virus shares 79.5% of genetic sequence with SARS-CoV and has 96.2% homology to a bat coronavirus.2 In addition, 2019-nCoV shares the same cell entry receptor, ACE2, with SARS-CoV. What is yet unclear is which animal is the intermediate species between bats and humans. For SARS it was civet cats, for MERS it is camels. While the source of 2019-CoV is yet unknown, early on the Huanan Seafood Wholesale Market was linked epidemiologically.1,5
The incubation period of this virus has been reported to be 5.2 days (95% CI, 4.1-7.0),6 although there is suggestion that it may be as long as 14 days. It is unclear when transmission begins and, although cases have been reported that suggest transmission during the asymptomatic phase, it is likely that the majority of secondary cases come from symptomatic individuals.
The clinical syndrome is nonspecific and characterized by fever and dry cough in the majority of patients, with about a third experiencing shortness of breath. Some patients have other symptoms such as myalgias, headache, sore throat, and diarrhea7. The median age of patients is between 49 and 56 years.7,8 Cases in children have been rare. Although most cases appear to be mild, all patients admitted to the hospital have pneumonia with infiltrates on chest x-ray and ground glass opacities on chest computed tomography.8,9 About a third of patients subsequently developed acute respiratory distress syndrome and required care in the intensive care unit. This is particularly true for patients with comorbid conditions such as diabetes or hypertension.8
When a patient presents with fever and respiratory symptoms (in particular a dry cough), clinicians should obtain a detailed travel history. If the patient has a history of travel to Hubei Province in the last 14 days, they should be considered a person under investigation (PUI) (Figure).