key: cord-1000782-petj3uk0
authors: Ward, John W.; del Rio, Carlos
title: The COVID‐19 Pandemic: An Epidemiologic, Public Health, and Clinical Brief
date: 2020-05-21
journal: Clin Liver Dis (Hoboken)
DOI: 10.1002/cld.973
sha: ebb8d8b220051e92ffbe92abbf82924397a88e37
doc_id: 1000782
cord_uid: petj3uk0

nan

The COVID-19 Pandemic Ward and del Rio review US epidemic accelerated, with cases doubling every 6 to 7 days. 7 By March 29, 2020, more than 100,000 persons had COVID-19 in the United States, the largest burden of COVID-19 globally. 2, 7 As of April 29, 2020, the COVID-19 pandemic has grown to more than 3 million confirmed cases and more than 206,000 deaths in 179 countries. The United States now has more than 1 million cases (33%) and more than 50,000 deaths (25%). 2, 7 The potential is high for large COVID-19 epidemics in Brazil, Russia, India, and many African countries.

SARS-CoV-2 is transmitted directly through inhalation or mucosal surface exposure to an infected person's respiratory droplets or indirectly when touching the face after contact with contaminated objects. 2, 4, 7 SARS-CoV-2 can remain viable on environmental surfaces for up to 72 hours. 8 SARS-CoV-2 is highly infectious with an R0 of approximately 2.2 to 3.0, meaning each infected person will infect about two to three other persons. 7 Large COVID-19 outbreaks have occurred in health care facilities, households, cruise ships, religious services (e.g., funerals), and other large gatherings 1,2,7 Individuals can transmit SARS-CoV-2 before, during, and after symptomatic disease. As many as half of individuals with SARS-CoV-2 infection have no symptoms. 7

Similar to SARS-CoV, SARS-CoV-2 binds to angiotensin-converting enzyme 2 (ACE2) receptors for entry via endocytosis into alveolar epithelial cells, as well as other cells with ACE2 receptors in the heart, gastrointestinal tract, and kidneys. 2,4 COVID-19 results from SARS-CoV-2 replication, causing early cell death (i.e., apoptosis) and provoking a storm of proinflammatory cytokines (e.g., interleukin-6 [IL-6]) disrupting alveolar walls with resulting fluid accumulation in alveoli. 4 The incubation period from infection to onset of COVID-19 disease is typically 5 to 7 days (range 1-14 days). 1, 2, 7 The most common symptoms of COVID-19 are fever and nonproductive cough (Table 1) . 1, 4, 7, 9 The Centers for Disease Control and Prevention (CDC) recently added anosmia and ageusia, the loss of smell and taste, as COVID-19 symptoms. 7 Laboratory findings are remarkable for a normal leukocyte count, lymphopenia, and elevated C-reactive protein. 1, 6, 8 Most hospitalized patients with COVID-19 have a bilateral ground-glass appearance on chest computed tomography (CT) scan consistent with viral pneumonia.

Today, reverse transcription polymerase chain reaction (RT-PCR) is the COVID-19 diagnostic test. 2,7 RT-PCR sensitivity is highest for testing bronchial alveolar lavage fluid (93%) and declines for sputum (72%) and nasal swab (63%) specimens. 10 COVID-19 diagnosis might require repeat testing. 2, 7 Serological tests to detect SARS-CoV-2 IgM and IgG antibodies are available. However, because of test sensitivity and other quality concerns, the US Food and Drug Administration (FDA; https://www.fda.gov) advises current serological tests are best used for surveillance and research, and not as the sole basis for COVID-19 diagnosis.

COVID-19 is commonly a mild disease. Of the first 72,314 COVID-19 disease reported in China, 81% had no or mild pneumonia, 21% had severe dyspnea and CoV-2

The COVID-19 Pandemic Ward and del Rio review radiological evidence of pulmonary disease, and 5% progressed to SARS. 1 Individuals can be ill for a week or longer before experiencing severe symptoms.

The risk for severe COVID-19 disease is highest for men, older adults, and patients with certain comorbidities. In the United States, 80% of reported COVID-19-related deaths are among people aged ≥65 years. 7, 9, 11 Deaths are rare among persons <24 years of age. 1, 7, 11 In the United States, most hospitalized patients with COVID-19 have comorbid conditions, including obesity, hypertension, diabetes, and cardiovascular disease 7, 11 (Table 2) . Although listed by the CDC as a comorbid condition associated with severe COVID-19, chronic liver disease, including cirrhosis, has not been a common comorbidity associated with hospitalization in the United States ( Table 2 ). The high prevalence of comorbid conditions can explain, in part, African Americans' increased risk for hospitalization with COVID-19 disease. 5 Variable comorbidity prevalence contributes to differences in national COVID mortality. Globally, crude fatality rates for COVID-19 range from 0.2% in Singapore, to 2.0% to 3.0% in South Korea and Germany, to 4.3% for the United States, and to 10% to 13% in Spain, Italy, and the United Kingdom. 2, 5 The search for effective therapies and a vaccine is occurring at a remarkable pace, with at least 29 studies of therapeutic agents and 5 studies of candidate vaccines registered on ClinicalTrials.org (https://www.clini caltr ials. gov). On May 1, 2020, the FDA granted Emergency Use Authorization of remdesivir, a broad-spectrum antiviral nucleotide prodrug for treatment of severe COVID-19. Studies of monoclonal antibodies against IL-6 and hyperimmune immunoglobulin are in progress. Following reports of serious cardiac arrythmias, the FDA cautioned clinicians of prescribing hydroxychloroquine or chloroquine for treatment of COVID-19. A safe and effective vaccine, if successfully developed, probably will not be available for 12 to 18 months.

In the absence of a vaccine, prevention is composed of a combination of nonpharmacological interventions 

The COVID-19 Pandemic Ward and del Rio review for suppression of transmission to R0 <1 and mitigation of the number of patients with COVID-19 who require intensive care and mechanical respiratory support. 12 Interventions include improved personal hygiene promotions, symptomatic screening and laboratory testing for case detection, contact tracing, household quarantine of those with transmission risks, and social distancing ( Table 3 ). The United States and most other countries have implemented extensive travel restrictions, workplace and school closures, and cancellation of sporting and other large public events. China, South Korea, and Taiwan successfully curbed large COVID-19 epidemics with prompt scale-up of testing, contact tracing, and quarantine. 2, 4, 7 In the United States, although testing rates are low, models suggest prevention measures are reducing transmission and future deaths. 13 The US government recently recommended increased COVID-19 surveillance, testing, and contact tracing with modified social distancing measures to sustain SARS-CoV-2 prevention while opening up education and commerce. 14 sUMMarY SARS-CoV-2 is a new human pathogen, readily spread via respiratory droplets and the cause of the growing COVID-19 pandemic. Men, older adults (>65 years old), and persons with comorbidities are at risk for severe COVID-19 and death. Countries have successfully suppressed transmission and mitigated needs for intensive care with robust case/contact detection (testing), isolation of infected/exposed persons, and social distancing. To stop the COVID-19 pandemic, the challenge is for all countries to scale up and sustain prevention measures while awaiting the arrival of effective vaccines and therapies. 

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