Middle East Respiratory Syndrome (MERS)

Infectious Agent

The MERS coronavirus, a single-stranded, positive-sense RNA coronavirus that belongs to the family Coronaviridae, genus Betacoronavirus .


Transmission dynamics are not well understood. The MERS coronavirus is genetically similar to bat coronaviruses and has been detected in camels in North Africa and the Arabian Peninsula. Although exposure to dromedary camels is a risk factor for MERS, little is known about the specific exposures that result in primary human cases. Evidence suggests that the virus can be spread from person to person among close contacts, resulting in outbreaks in families and in health care settings. Sustained community transmission of MERS has not been shown.


MERS coronavirus is an emerging novel coronavirus that causes severe acute respiratory illness, and approximately 35% of confirmed cases have been fatal. MERS was first reported in September 2012, but illnesses with onsets as early as April 2012 were subsequently documented. Risk is ongoing in countries in or near the Arabian Peninsula. Index cases have lived in or recently traveled to Iran, Jordan, Kuwait, Lebanon, Oman, Qatar, Saudi Arabia, United Arab Emirates, or Yemen. MERS has also been identified in travelers from these countries returning to North America, Europe, Asia, and North Africa.

Clinical Presentation

MERS is associated with severe acute respiratory failure, multiple organ dysfunction, and high mortality, although the spectrum of illness and clinical course are not fully defined. Mild or asymptomatic cases have been documented among contacts of cases. For people who develop symptomatic illness, the incubation period is approximately 2–14 days; median incubation period is slightly more than 5 days. Disease is most often characterized by fever, cough, and shortness of breath. Other symptoms may include chills, sore throat, myalgias, arthralgias, diarrhea, and vomiting. Initial nonspecific symptoms can progress to pneumonia. Chest radiographs have shown variable pulmonary involvement.

In addition to acute and often severe respiratory compromise, serious complications of MERS include cardiovascular collapse and acute renal injury. Abnormal laboratory findings can include thrombocytopenia, lymphopenia, and elevated liver function tests. Older age and comorbidities are associated with poor outcomes.


Several diagnostic assays have been developed to detect acute infection with MERS coronavirus, including real-time RT-PCR. Lower respiratory specimens (sputum, bronchoalveolar lavage, endotracheal aspirates) are the priority respiratory specimens for testing, although upper respiratory and serum specimens should also be collected, if possible. To increase the likelihood of detecting the virus, multiple specimens from these sites should be collected over the course of the illness. In the United States, most state laboratories are approved to test for MERS by using CDC’s RT-PCR assay. Testing should be coordinated through state and local health departments and CDC.

In coordination with state and local health departments, health care providers should evaluate patients for MERS if they develop fever and pneumonia or acute respiratory distress syndrome within 14 days after traveling from countries in or near the Arabian Peninsula or have had close contact with a recent traveler from this area who has fever and acute respiratory illness.


No specific antiviral treatment is available. Treatment is limited to supportive care. Standard, contact, and airborne infection-control precautions are recommended for hospitalized patients with known or suspected MERS.


No vaccine or preventive drug is available. CDC recommends that travelers practice general hygiene precautions such as frequent handwashing; avoiding touching the eyes, nose, and mouth; and avoiding contact with sick people. The World Health Organization (WHO) considers certain groups to be at high risk for severe MERS, including people with diabetes, kidney failure, chronic lung disease, or immunocompromised people. WHO recommends that these groups take additional precautions: avoid contact with camels, do not drink raw camel milk or raw camel urine, and do not eat undercooked meat, particularly camel meat. For more information, see www.who.int/csr/disease/coronavirus_infections/faq/en.

CDC website: www.cdc.gov/coronavirus/mers


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John T. Watson, Susan I. Gerber