History

The median incubation period of MERS infection is 5.2 days,^[28]but periods of up to 12 days have been described,^[29]thus ranging 4-14 days. Clinical manifestation is indistinguishable from other common respiratory viruses and may range from no symptoms to rapidly progressive multiorgan failure and death. The median time from onset to hospitalization is 4 days, with critically ill patients requiring intensive care within a median of 5 days from onset.

A high index of suspicion is necessary for MERS, and a travel and exposure history is essential to the diagnosis. Keys to the case definition of MERS is a history of residence or travel in the Arabian Peninsula, in countries where MERS-CoV is known to be circulating in dromedary camels, or where human infections have recently occurred and exposure within the incubation period of 14 days.^[30]

Upon suspicion of MERS, the patient should be placed in an airborne infection isolation room (AIIR) with a minimum of 12 air exchanges per hour, and personnel protection equipment (PEP) appropriate for contact and airborne precautions (gown, gloves, goggles, and N-95 respirator mask or powered air purifier respirator [PAPR]) should be used. Care should be taken to remove PEP without contact with contaminated outer surfaces.^[31]

Predictors of more severe disease and higher risk of mortality include hospital-acquired infection, older age, immune disorders, and comorbidities including diabetes, end-stage renal disease, malignancy, and chronic cardiac and pulmonary conditions.

The initial presentation of MERS includes flulike symptoms, including fever, chills, rhinorrhea, fatigue, and myalgias. Respiratory symptoms, including cough and dyspnea, may become prominent later in the course. Pneumonitis is common. Gastrointestinal symptoms including anorexia, nausea, diarrhea, and abdominal pain have been reported.^{[3, 32]}

Physical Examination

Physical examination findings associated with MERS-CoV infection are similar to those presenting with any flulike illness, including the following:

Fever
Rhinorrhea, mostly clear
Pulmonary findings, including hypoxemia, rhonchi, and rales (some patients may have a normal auscultation)
Tachycardia
Hypotension may occur with severe illness, reflecting systemic inflammatory response syndrome

Complications

In more severe cases of MERS, patients who develop pneumonitis and acute respiratory failure develop severe hypoxemia and require mechanical ventilation and possibly oxygen rescue therapy such as extracorporeal membrane oxygenation (ECMO). Vasopressor support and renal replacement therapy are often also required.^[33]

Differential Diagnoses

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Media Gallery

Vero cells infected with Middle East respiratory syndrome coronavirus (MERS-CoV). Image courtesy of the Centers for Disease Control and Prevention (Jennifer L. Harcourt).
MERS-CoV virion on electron microscopy, illustrating ultrastructural detail. Image courtesy of the Centers for Disease Control and produced by the National Institute of Allergy and Infectious Diseases (NIAID), 2014.