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.
Four coronaviruses (229E, OC43, NL63, and HKU1) most frequently cause symptoms of the common cold. Rarely, severe lower respiratory tract infections, including bronchiolitis and pneumonia, can occur, primarily in infants, older adults, and the immunocompromised.
Three 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-CoV-2 is the cause of coronavirus disease 2019 (COVID-19).
MERS-CoV was identified in 2012 as the cause of Middle East respiratory syndrome (MERS).
SARS-CoV-1 was identified in 2003 as the cause of an outbreak of severe acute respiratory syndrome (SARS) that began in China in 2002.
These coronaviruses that cause severe respiratory infections are zoonotic pathogens, which begin in infected animals and are transmitted from animals to people. SARS-CoV-2 has significant person-to-person transmission.
Middle East Respiratory Syndrome (MERS)
Middle East respiratory syndrome (MERS) is a severe, acute respiratory illness caused by the MERS coronavirus (MERS-CoV).
MERS-CoV infection was first reported in September 2012 in Saudi Arabia (1), but an outbreak in April 2012 in Jordan was confirmed retrospectively (2). Through 2022, worldwide, over 2500 cases of MERS-CoV infection (with over 900 related deaths) have been reported from 27 countries (3); all cases of MERS have been linked through travel to or residence in countries in and near the Arabian Peninsula, with > 80% involving Saudi Arabia. The largest known outbreak of MERS outside the Arabian Peninsula occurred in the Republic of Korea in 2015 (4). The outbreak was associated with a traveler returning from the Arabian Peninsula. Cases have also been confirmed in countries throughout Europe, Asia, North Africa, the Middle East, and the United States in patients who were either transferred there for care or became ill after returning from the Middle East. Only a handful of cases have been reported since 2019 (3).
The World Health Organization considers the risk of contracting MERS-CoV infection to be very low for people traveling to Saudi Arabia for Umrah and Hajj.
Median age of patients with MERS-CoV is about 50 years, and patients are predominantly male. Infection tends to be more severe in older adults and in patients with a preexisting disorder such as diabetes, a chronic heart disorder, or a chronic renal disorder.
Transmission of MERS-CoV
MERS-CoV may be transmitted from person to person via direct contact, respiratory droplets (particles > 5 micrometers), or aerosols (particles < 5 micrometers).
The reservoir of MERS-CoV is thought to be dromedary camels, but the mechanism of transmission from camels to humans is unknown. Most reported cases involved direct human-to-human transmission in health care settings. If MERS is suspected in a patient, infection control measures must be initiated promptly to prevent transmission in health care settings.
References
1. Zaki AM, van Boheemen S, Bestebroer TM, Osterhaus AD, Fouchier RA: Isolation of a novel coronavirus from a man with pneumonia in Saudi Arabia [published correction appears in N Engl J Med. 2013 Jul 25;369(4):394]. N Engl J Med. 2012;367(19):1814-1820. doi:10.1056/NEJMoa1211721
2. Hijawi B, Abdallat M, Sayaydeh A, et al: Novel coronavirus infections in Jordan, April 2012: epidemiological findings from a retrospective investigation. East Mediterr Health J. 2013;19 Suppl 1:S12-S18.
3. World Health Organization Middle East respiratory syndrome: Global summary and assessment of risk. 16 November 2022. Accessed April 2024.
4. Ki M: 2015 MERS outbreak in Korea: hospital-to-hospital transmission. Epidemiol Health. 2015;37:e2015033. Published 2015 Jul 21. doi:10.4178/epih/e2015033
Symptoms and Signs of MERS
The incubation period for MERS-CoV is about 5 days.
Initially, most reported cases have involved severe respiratory illness requiring hospitalization, with a case fatality rate of approximately 35%; however, approximately 21% of patients had mild or no symptoms (1). Between 2019 and 2022 only 5% of reported cases were asymptomatic or had mild disease, but this decrease was likely due to reductions in testing and case detection as a result of the ongoing COVID-19 pandemic and not due to a change in virulence.
Fever, chills, myalgia, and cough are common. Gastrointestinal symptoms (eg, diarrhea, vomiting, abdominal pain) occur in about one third of patients. Manifestations may be severe enough to require treatment in an intensive care unit, but the proportion of such cases has declined sharply over time.
Symptoms and signs reference
1. World Health Organization Middle East respiratory syndrome: Global summary and assessment of risk. 16 November 2022. Accessed April 2024.
Diagnosis of MERS
Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) testing of upper and lower respiratory secretions and serum
MERS should be suspected in patients who have an unexplained acute febrile lower respiratory infection and who have had any of the following within 14 days of symptom onset:
Travel to or residence in an area where MERS has recently been reported or where transmission could have occurred
Contact with a health care facility where MERS has been transmitted
Close contact with a patient who was ill with suspected MERS
MERS should also be suspected in patients who have had close contact with a patient with suspected MERS and who have a fever whether they have respiratory symptoms or not.
Practice guidelines are available from the Centers for Disease Control and Prevention (CDC) (MERS: Information for Healthcare Professionals).
Testing should include real-time RT-PCR testing of upper and lower respiratory secretions, ideally taken from different sites and at different times. Serum should be obtained from patients and from all, even asymptomatic close contacts, including health care workers (to help identify mild or asymptomatic MERS). Serum is obtained immediately after MERS is suspected or after contacts are exposed (acute serum) and 3 to 4 weeks later (convalescent serum). Testing is done at state health departments or the CDC.
In all patients, chest imaging detects abnormalities, which may be subtle or extensive, unilateral or bilateral. In some patients, levels of lactate dehydrogenase (LDH) and aspartate aminotransferase (AST) are elevated and/or levels of platelets and lymphocytes are low. A few patients have acute kidney injury. Disseminated intravascular coagulation and hemolysis may develop.
Treatment of MERS
Supportive treatment
Treatment of MERS is supportive. To help prevent spread from suspected cases, health care professionals should use standard, contact, and airborne precautions.
There is no vaccine.
See also World Health Organization: Clinical management of severe acute respiratory infection when Middle East respiratory syndrome coronavirus (MERS-CoV) infection is suspected. Interim guidance, Updated January 2019.
Severe Acute Respiratory Syndrome (SARS)
Severe acute respiratory syndrome (SARS) is a severe, acute respiratory illness caused by the SARS coronavirus (SARS-CoV-1).
SARS is a severe coronavirus infection with a case fatality rate of approximately 15%, but the fatality rate much higher in older adults (1). SARS is an influenza-like illness that occasionally leads to progressively severe respiratory insufficiency.
SARS-CoV-1 was first detected in the Guangdong province of China in November 2002 and subsequently spread to 28 additional countries (2). In this outbreak, > 8000 cases were reported worldwide, with 774 deaths (approximately a 10% case fatality rate, increased significantly with age, with a mortality rate > 50% in those > 65 years-old) (3, 4). The SARS-CoV-1 outbreak was the first time that the Centers for Disease Control and Prevention (CDC) advised against travel to a region. This outbreak subsided, and no new cases have been identified since 2004. The immediate source was presumed to be civet cats, that were being sold for food in a live-animal market and had likely been infected through contact with a bat before they were captured for sale. Bats are frequent hosts of coronaviruses.
SARS-CoV-1 is transmitted from person to person by close personal contact. It is thought to be transmitted most readily by respiratory droplets produced when an infected person coughs or sneezes.
Diagnosis of SARS is made clinically, and treatment is supportive. Coordination of prompt and rigid infection control practices helped control the 2002 outbreak rapidly.
Although no new cases have been reported since 2004, SARS should not be considered eliminated because the causative virus has an animal reservoir from which it conceivably could reemerge.
SARS references
1. World Health Organization: Consensus document on the epidemiology of severe acute respiratory syndrome (SARS), 2003, WHO/CDS/CSR/GAR/2003.11
2. Cherry JD: The chronology of the 2002-2003 SARS mini pandemic. Paediatr Respir Rev. 2004;5(4):262-269. doi:10.1016/j.prrv.2004.07.009
3. CDC Morbidity and Mortality Weekly Report: Revised U.S. Surveillance Case Definition for Severe Acute Respiratory Syndrome (SARS) and Update on SARS Cases --- United States and Worldwide, 52(49);1202-1206, 2003
4. Peiris JS, Yuen KY, Osterhaus AD, et al: The severe acute respiratory syndrome. N Engl J Med 349(25):2431-41, 2003. doi: 10.1056/NEJMra032498. PMID: 14681510
