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The Epidemiology of the Omnipresent Coronavirus

Roberts, James R. MD

doi: 10.1097/01.EEM.0000731736.21884.56
    COVID-19, coronavirus, pandemic, epidemiology
    COVID-19, coronavirus, pandemic, epidemiology:
    This illustration from the Centers for Disease Control and Prevention reveals the ultrastructure morphology of the novel coronavirus. Note the spikes that adorn the outer surface of the virus, imparting the look of a corona surrounding the virion, when viewed through an electron microscope. This virus, named the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was identified as the cause of a rapidly spreading respiratory illness first detected in 2019, hence the name coronavirus disease 2019 (COVID-19).

    I hesitated to write about the coronavirus because we are inundated almost daily with new information, and everything is constantly changing. What is known today will, in all likelihood, be different or modified in a few weeks. But I will try to focus things a bit. Emergency Medicine News has published a number of superb articles with current coronavirus information relevant to emergency physicians; just visit the website to read a few (or 50):

    The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was identified at the end of 2019 as the cause of a cluster of cases of pneumonia in Wuhan, China. This disease quickly spread throughout China, and was followed quite rapidly by a global pandemic. No other viral infection has spread so rapidly and caused such morbidity in recent years. More than 250,000 Americans have died from this disease, and more than nine million people have been infected in the United States alone.

    No emergency physician can work for any length of time and not see numerous COVID-19 cases. The infection is important in bona fide ED patients, but it can readily infect emergency staff. The virus can be transmitted through normal social interaction with amazing speed and ease. Simply being in a closed room for any length of time with an infected individual can almost guarantee that anyone not wearing protective equipment will become infected. Unfortunately, asymptomatic individuals can readily spread the disease.

    This month starts a discussion of COVID-19 by defining the biology and epidemiology of the virus.

    Clinical Characteristics of Coronavirus Disease 2019 in China

    Guan W, Ni Z, et al. N Engl J Med. 2020;382(18):1708

    This report describes 1099 patients with laboratory-confirmed COVID-19 infections from 552 hospitals in China through January 2020. The first cases of pneumonia of an unknown origin were identified the month before in Wuhan, the capital city of Hubei Province. The pathogen was identified as an RNA coronavirus that has since spread worldwide. The authors reviewed the medical records of patients with a positive polymerase chain reaction (PCR) assay of a nasal pharyngeal swab; only laboratory-confirmed cases were included in the analysis. The authors reviewed clinical signs and symptoms documented in the hospital record, laboratory findings, and radiographic assessments via a chest x-ray or chest CT. The primary endpoint was admission to the ICU, the use of mechanical ventilation, or death. The outcomes of 1099 patients were reported, and this was the first large-scale scientific report of COVID-19.

    A total of 3.5 percent of individuals were health care workers. The medium incubation period from known exposure was four days, the median age of patients was 47 years, and only one percent of patients were under 15. Fever was present in 43 percent on admission, but 89 percent of patients subsequently developed one during hospitalization. The most common presenting symptoms were cough (68%), nausea and vomiting (5%), and diarrhea (4%). A coexisting illness, such as hypertension or COPD, was present in 24 people. A chest CT scan was abnormal in 86 percent, the most common finding being diffuse ground glass opacities and bilateral patchy infiltrates. Lymphocytopenia was present in 83 percent, thrombocytopenia in 36 percent, and leukopenia in 34 percent upon admission.

    The primary composite endpoint occurred in only six percent of the 1099 patients. Of all patients, only 3.6 percent were admitted to the ICU, 2.3 percent underwent invasive mechanical ventilation, and 1.4 percent died. These endpoints were seen in 21 percent of those with a severe coexisting disease. The majority of patients (58%) received intravenous antibiotics, and oxygen therapy was administered in 42 percent. The median duration of hospitalization was 12 days.

    COVID-19 in Critically Ill Patients in the Seattle Region-Case Series

    Bhatraju PK, Ghassemieh BJ, et al. N Engl J Med. 2020;382(21):2012

    This first report of cases in the United States reviews the clinical characteristics of 24 patients with confirmed COVID-19. These authors evaluated patients with a positive PCR assay from a nasal pharyngeal swab. The mean age was 64 (±18), 63 percent were men, and the duration of symptoms before hospitalization was seven days (±4). No patient had traveled to China. All had hypoxic respiratory failure, and 75 percent required mechanical ventilation, with a median duration of 10 days.

    Most patients had hypotension and required vasopressors. The most common symptoms upon admission were shortness of breath, cough, and fever, though only 50 percent had a fever on admission. All patients had bilateral pulmonary opacities on chest x-ray. Twelve of the 24 patients died. Diabetes was an underlying condition in 58 percent. Blood and sputum cultures failed to reveal a bacterial source, and no patient was positive for influenza or another respiratory virus.

    Comment: Coronaviruses are RNA viruses similar to the organism that causes severe acute respiratory distress syndrome (SARS). Person-to-person respiratory spread is the primary means of transmission. Transmission is thought to occur via respiratory droplets released when a patient coughs, sneezes, or talks directly and closely to another person. Such infectious droplets may remain in the air for a few hours. Transmission may also occur by touching contaminated surfaces on which the virus had been deposited. SARS-CoV-2 has been detected in nonrespiratory specimens, including stool, but the role of other sites in transmission is uncertain.

    The virus can live for many days on a number of surfaces. Apparently, droplets typically do not travel more than about six feet, hence the current social distancing recommendations. Importantly, the potential to transmit this virus begins before symptoms develop, and transmission is highest in the early course of the illness. Transmission after seven to 10 days of illness is thought to be unlikely, and the spread from infected individuals without symptoms has been well documented. This characteristic makes this virus readily transmitted from individuals who do not appear ill. Most infections, about 80 percent, are clinically mild. Severe disease is present in about 15 percent and critical disease in about five percent. The overall fatality rate is two to three percent, and 60 percent of those requiring mechanical ventilation will die.

    Asymptomatic infections of COVID-19 have been well documented, and as many as 30 to 40 percent of infected patients can remain asymptomatic. More than half of infected asymptomatic individuals will have positive findings on chest CT. The illness can occur in otherwise healthy individuals of any age, but severe disease usually occurs in older adults with underlying medical comorbidity. Associated comorbidities are the common ones, such as cardiovascular disease, diabetes, hypertension, chronic lung disease, cancer, chronic kidney disease, obesity, and smoking. Lab abnormalities are common in those with a poor outcome, including lymphocytopenia, thrombocytopenia, elevated liver enzymes, an elevated D-dimer, and signs of acute kidney injury.

    Interestingly, fever is not always present early in this disease, and may not always develop in those who become ill. COVID-19 is a respiratory illness, so an abnormal chest x-ray is routine. A CT scan is more sensitive for finding the common bilateral patchy ground glass opacities, but CT scan results do not usually change management. Pleural effusions are not common. Loss of taste and smell, often for a prolonged period, is a curious finding in those infected.

    This disease is associated with long-term sequelae. Recovery time is variable, usually two to six weeks, depending on the severity of the illness. Only about 40 percent of those hospitalized report a return to baseline by 21 days. Of those mechanically ventilated, only about 13 percent will be symptom-free 60 days after onset. The most common persistent symptoms, which can last for weeks to months, are fatigue, cough, dyspnea, joint pain, and chest pain. Those critically ill can have rather prolonged persistent impairment in cognition, overall mental health, and decreased physical function.

    Pregnancy does not appear to increase susceptibility to COVID-19 infection, and most infected patients fully recover without undergoing delivery. Pregnant women can avoid exposure by following the general recommendations: physical distancing, wearing a face covering, and avoiding indoor groups of people and crowded spaces, such as bars and restaurants. Washing or sanitizing hands and disinfecting frequently touched surfaces are recommended. Clinical manifestations of COVID-19 in pregnant women are generally similar to those in others with the virus. Pregnant women with a history of contact with a person who has confirmed, probable, or suspected COVID-19 infection should self-isolate for 14 days and be monitored for symptoms.

    Emergency delivery is not indicated for women with preterm COVID-19 and nonsevere illness who have no medical indications for prompt delivery. Ideally, a normal delivery will occur sometime after a negative test result is obtained or isolation status is lifted, minimizing the risk of postnatal infection.

    COVID-19 is not an indication to alter the route of delivery. Most pregnant patients (at least 85%) with known or suspected COVID-19 have mild disease that does not warrant hospital care. Pregnant women with mild disease and comorbidities (poorly controlled hypertension, gestational or pregestational diabetes, chronic renal disease, chronic cardiopulmonary disease, or other immunosuppressive conditions) or those with moderate to severe disease should be hospitalized. Emergency clinicians should consult OB/GYN on most pregnant patients with known or suspected infection.

    Children of all ages can get COVID-19, but the young are less commonly affected and have milder symptoms than adults. (New Engl J Med. 2020;382[17]:1663; U.S. children under 18 account for approximately eight to 10 percent of cases, and infection usually results from household exposure but can be transmitted from other students, teachers, or school staff. A minority of children (2-4%) with COVID-19 require hospitalization. Fever, cough, and shortness of breath are the most commonly reported symptoms, but other common symptoms include myalgia, sore throat, headache, and nausea and diarrhea. Like adults, children with underlying medical conditions are at greater risk for severe disease and the need for hospitalization, intensive care, and mechanical ventilation. There have been increasing reports of a rare and poorly understood multisystem inflammatory syndrome similar to Kawasaki disease associated with COVID-19 infections in children. Knowledge of this condition is evolving.

    COVID-19-specific antibodies and cell-mediated responses are induced following infection. Most of these responses are protective, but the specifics of immunity must still be definitively established. It is unknown whether all infected patients mount a protective immune response or how long any protective effect will last. Reinfection seems to occur rarely.

    Possible Risk Factors Predisposing to Severe COVID-19 Infection∗

    • Cancer
    • Chronic kidney and liver disease
    • COPD
    • Organ transplant
    • Obesity
    • Smoking
    • Heart failure
    • Coronary artery disease
    • Cardiomyopathy
    • Sickle cell disease
    • Diabetes
    • Increased age

    ∗All underlying medical conditions predispose to more serious COVID-19 infections.

    Patient Characteristics in More Than 370,000 Confirmed Cases of COVID-191

    • Hospitalization: 14%2
    • Cough: 50%
    • Fever (subjective or >100.4°F/38°C): 43%
    • Myalgia: 36%
    • Headache: 34%
    • Dyspnea: 29%
    • Sore throat: 20%
    • Diarrhea: 19%
    • Nausea/vomiting: 12%
    • Loss of smell/taste: <10%
    • Abdominal pain: <10%
    • Rhinorrhea: <10%
    • Death: 5%3

    1. Symptoms are nonspecific and can be seen with a number of viral illnesses.

    2. Hospitalizations were six times higher (45%) among patients with underlying medical conditions than those without them (8%).

    3. Death in those with underlying medical conditions (20%) was 12 times higher than in those without them (1.6%).

    Source: MMWR: Morb Mortal Wkly Rep. 2020;69[24]:759;

    Resources for the Latest COVID-19 Information

    CME for InFocus!

    Earn CME by completing a quiz about this article. You may read the article here, on our website, or in our iPad app, and then complete the quiz, answering at least 70 percent of the questions correctly to earn CME credit. The cost of the CME exam is $10. The payment covers processing and certificate fees.

    Visit for more information about this educational offering and to complete the CME activity. This enduring material is available to physicians in all specialties, nurses, and other allied health professionals. Lippincott Continuing Medical Education Institute, Inc., is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. Lippincott Continuing Medical Education Institute, Inc., designates this enduring material for a maximum of 1 AMA PRA Category 1 Credit™. Physicians should only claim credit commensurate with the extent of their participation in the activity. This activity expires Dec. 31, 2022.

    Learning Objectives for This Month's CME Activity: After participating in this CME activity, readers should be better able to describe how the SARS-CoV-2 virus is spread and explain how it affects infected patients.

    Dr. Robertsis a professor of emergency medicine and toxicology at the Drexel University College of Medicine in Philadelphia. Read the Procedural Pause, a blog by Dr. Roberts and his daughter, Martha Roberts, ACNP, PNP, at, and read his past columns at

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