Coronaviruses and Acute Respiratory Syndromes (COVID-19, MERS, and SARS)

Coronaviruses are enveloped RNA viruses that cause respiratory illnesses of varying severity from the common cold to fatal pneumonia. 

Numerous coronaviruses, first discovered in domestic poultry in the 1930s, cause respiratory, gastrointestinal, liver, and neurologic diseases in animals. Only 7 coronaviruses are known to cause disease in humans. 

Four of the 7 coronaviruses most frequently cause symptoms of the common cold

Coronaviruses 229E and OC43 cause the common cold; the serotypes NL63 and HUK1 have also been associated with the common cold. 

Rarely, severe lower respiratory tract infections, including pneumonia, can occur, primarily in infants, older people, and the immunocompromised.

Three of the 7 coronaviruses cause much more severe, and sometimes fatal, respiratory infections in humans than other coronaviruses and have caused major outbreaks of deadly pneumonia in the 21st century:

  • SARS-CoV2 is a novel coronavirus identified as the cause of coronavirus disease 2019 (COVID-19) that began in Wuhan, China in late 2019 and spread worldwide.

  • MERS-CoV was identified in 2012 as the cause of Middle East respiratory syndrome (MERS).

  • SARS-CoV was identified in 2002 as the cause of an outbreak of severe acute respiratory syndrome (SARS).

These coronaviruses that cause severe respiratory infections are zoonotic pathogens, which begin in infected animals and are transmitted from animals to people.

COVID-19 is an acute, sometimes severe, respiratory illness caused by a novel coronavirus SARS-CoV2.

COVID-19 was first reported in late 2019 in Wuhan, China and has since spread extensively in China and worldwide. 

Transmission of COVID-19

Early COVID-19 cases were linked to a live animal market in Wuhan, China, suggesting that the virus was initially transmitted from animals to humans. 

Person-to-person spread occurs through contact with infected secretions, mainly via contact with large respiratory droplets, but it could also occur via contact with a surface contaminated by respiratory droplets. 

Researchers are still learning how readily this virus spreads from person to person or how sustainable infection will be in a population, although it appears more transmissible than SARS and spread is probably more similar to that of influenza.

Super-spreaders played an extraordinary role in driving the 2003 SARS outbreak and may also play a significant role in the current COVID-19 outbreak. 

A super-spreader is an individual who transmits an infection to a significantly greater number of other people than the average infected person. 

Quarantine and isolation measures are being applied in an attempt to limit the local, regional, and global spread of this outbreak.

Symptoms and Signs

People with COVID-19 may have few to no symptoms, although some become severely ill and die. Symptoms can include fever, cough, and shortness of breath. 

Those with more severe disease may have lymphopenia and chest imaging findings consistent with pneumonia. 

The exact incubation time is not certain; estimates range from 1 to 14 days. The risk of serious disease and death in COVID-19 cases increases with age.

Symptoms and signs reference

1. Centers for Disease Control and Prevention: Severe Outcomes Among Patients with Coronavirus Disease 2019 (COVID-19) — United States, February 12–March 16, 2020. MMWR Morb Mortal Wkly Rep 69:343-346, 2020. doi: 10.15585/mmwr.mm6912e2external icon.


Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) testing of upper and lower respiratory secretions.

Diagnostic testing for COVID-19 is being made available to select laboratories authorized by the Federal Drug Administration under an Emergency Use Authorization (EUA). 

Clinicians can also access laboratory testing through public health laboratories in their jurisdictions.

For initial diagnostic testing for COVID-19, the CDC recommends collecting and testing a single upper respiratory nasopharyngeal swab. 

Collection of only oropharyngeal swabs is acceptable if other swabs are not available. 

The CDC also recommends testing lower respiratory tract specimens, if available. 

For patients for whom it is clinically indicated (eg, those receiving invasive mechanical ventilation), a lower respiratory tract aspirate or bronchoalveolar lavage sample should be collected and tested as a lower respiratory tract specimen. 

Collection of oropharyngeal swabs is a lower priority and if collected should be combined in the same tube as the nasopharyngeal swab. 

Collection of sputum should be done only for those patients with productive coughs. Induction of sputum is not recommended. 

Specimens should be collected as soon as possible, regardless of the time of symptom onset. 

Maintain proper infection control when collecting specimens. 

For biosafety reasons, the CDC recommends local institutions do not attempt to isolate the virus in cell culture or do initial characterization of viral agents in patients suspected of having COVID-19 infection.

Because of the increasing availability of test kits in the US, previous restrictions on patient selection for testing are being relaxed, and testing is expanded to a wider group of symptomatic patients. 

Clinicians should use their judgment as to whether a patient’s symptoms and signs are compatible with COVID-19 and whether they should be tested. 

Decision to test should also take into account the local epidemiology of COVID-19, the course of illness, and the patient’s epidemiologic factors such as close contact with a confirmed COVID-19 case within 14 days of symptom onset or history of travel to an affected geographic area within 14 days of symptom onset. 

Clinicians are also strongly encouraged to test for other causes of similar respiratory illness (eg, influenza). 

Areas of sustained transmission will vary as the outbreak proceeds. For areas inside the US, clinicians should consult state or local health departments. 

For countries outside the US, affected areas as of March 5, 2020 include China, Iran, Italy, Japan, and South Korea.

If any of these criteria are present, infection control personnel at the healthcare facility and the local or state health department should be notified immediately.


Supportive Treatment of COVID-19 is supportive. No vaccine, antiviral drug, or other specific treatment is available.

To help prevent spread from suspected cases, health care practitioners should use standard, contact, and airborne precautions with eye protection.

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