Coronaviruses are RNA viruses that infect humans, birds and other mammals causing disease involving the respiratory, gastrointestinal and neurologic systems. While most coronaviruses cause mild respiratory illness consistent with the common cold, two lethal coronaviruses have been previously identified, including the acute respiratory syndrome coronavirus (SARS-CoV) in 2002 demonstrating 10% mortality and the Middle East respiratory syndrome coronavirus (MERS-CoV) in 2012 producing 37% mortality. 

In December 2019, a novel coronavirus (2019-nCoV) was isolated from a cluster of patients with pneumonia in Wuhan, China, a large city with a population of 11 million people. As reported in the Lancet, two thirds of the initial affected patients had a history of exposure to the Huanan seafood market, which was shut down on January 1, 2020.¹ Nucleic acids from bronchoalveolar lavage fluid samples of 3 patients were tested for 18 viruses and 4 bacteria by polymerase chain reaction (PCR) and reverse transcription PCR (RT-PCR).⁵  Isolated RNA was used to clone and sequence the genome of the 2019-nCoV, which was observed to be most similar to a SARS-like betacoronavirus previously isolated from bats. Therefore, 2019-nCoV is hypothesized to have a primary reservoir in bats, but the means of transmission directly to humans or through an intermediary host has not been elucidated. While the first reports of infection suggested this zoonotic coronavirus had limited or no human-to-human transmission, we have now learned that interhuman transmission has occurred since the middle of December, 2019.³  The most recent data estimates the mean incubation period to be approximately 5 days.  However, transmission was observed to occur in as few as 3 days after exposure to an initially asymptomatic individual in Vietnam, who later developed symptomatic infection and tested positive for 2019-CoV by RT-PCR.²

A case series of 41 patients in Wuhan, China with confirmed 2019-nCoV revealed that the most common presenting symptoms include fever (98%), cough (76%), dyspnea (55%) and myalgias (44%).¹  The median age was 49 years. Less than half of patients had comorbid conditions, like diabetes or cardiovascular disease. One third of patients required admission to the intensive care unit (ICU), typically for respiratory support for acute hypoxic respiratory failure. Dyspnea occurred at a median of 8 days after symptom onset and acute respiratory distress syndrome (ARDS) developed at a median of 9 days. Most patients had a normal procalcitonin level (< 0.1 ng/mL). Chest CT was abnormal in all cases consistent with pneumonia and 98% of patients had bilateral consolidation and/or ground glass opacity. ARDS developed in 29% of patients. All patients were treated empirically for influenza and bacterial pneumonia. Methyprednisolone (40-120 mg per day) was administered when severe community-acquired pneumonia was diagnosed. The observed mortality in this case series of patients with 2019-nCoV was 15% and as of January 22, 2020, 68% of the cohort was discharged. More recent mortality rate estimates comprising nearly 800 reported cases are closer to 3%.⁴  

The clinical presentation of patients infected with 2019-nCoV differs from SARS-CoV and MERS-CoV based on the absence of upper respiratory symptoms like rhinorrhea, sneezing or sore throat, localizing the novel virus to the lower airway. Additionally, gastrointestinal symptoms are less common with 2019-nCoV, while approximately one quarter of SARS-CoV and MERS-CoV patients had diarrhea. Increased amounts of inflammatory cytokines have been measured in all 3 lethal coronaviruses. Currently, no specific antiviral therapy for 2019-nCoV is available. The 2019-nCoV remains under intense monitoring by the CDC, given the risk of a pandemic. As directed by the CDC, healthcare workers must screen patients with fever, cough and dyspnea in the United States for travel to China or other affected regions (Table 1) in the past 2 weeks. Transmission of 2019-nCoV is suspected to occur by large droplets and contact rather than aerosols. Patients with suspected novel coronavirus infection should have a facemask placed over mouth and nose and be rapidly isolated in an airborne infection isolation room. Healthcare workers should adhere to standard contact and airborne isolation, utilize eye protection and perform hand hygiene with soap and water.⁶ 

Table 1.

References: 

1. Huang C, et al. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet [Internet]. 2020 Jan 24;1-10. Available from: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)30183-5/fulltext

2. Lan T et al. Importation and human-to-human transmission of a novel coronavirus in Vietnam. . New Engl J Med [Internet]. 2020 Jan 28;1-2. Available from: https://www.nejm.org/doi/full/10.1056/NEJMc2001272?query=featured_home

3. Li Q, et al. Early transmission dynamics in Wuhan, China, of novel coronavirus-infection pneumonia. New Engl J Med [Internet]. 2020 Jan 29;1-9. Available from: https://www.nejm.org/doi/full/10.1056/NEJMoa2001316?query=RP

4. Perlman S. Another decade, another coronavirus. New Engl J Med [Internet]. 2020 Jan 24;1-2. Available from: https://www.nejm.org/doi/full/10.1056/NEJMe2001126?query=featured_home

5. Zhu N, et al. A novel coronavirus from patients with pneumonia in China, 2019. New Engl J Med [Internet]. 2020 Jan 24;1-7. Available from: https://www.nejm.org/doi/pdf/10.1056/NEJMoa2001017?articleTools=true. 

6. Centers for Disease Control and Prevention (CDC): National Center for Immunization and Respiratory Diseases (NICRD), Division of Viral diseases. 2019 Novel Coronavirus, Wuhan, China. Retrieved from https://www.cdc.gov/coronavirus/2019-nCoV/clinical-criteria.html.