MERS: A Primer

Yesterday the CDC reported the first case of Middle East Respiratory Syndrome (MERS) in the United States. The patient is a healthcare worker who flew from Saudi Arabia to Chicago (via London), and then traveled by bus to Indiana, where he is currently hospitalized.

I suspect this is the first of many posts on this topic. In case you have not been following the MERS story, I put together a summary to get you up to speed.

  • Approximately 400 cases have been reported since the first case was reported in 2012.
  • All cases have been acquired in 6 countries in the Arabian peninsula, though some cases became symptomatic after travel to other countries.
  • The virus (a novel coronavirus) appears to have originated in bats, but antibodies to the virus have been found in camels.
  • Transmission dynamics are not completely understood. Human-to-human transmission does occur, and some cases are associated with contact with camels.
  • About 1 in 5 cases have been healthcare workers who cared for patients with MERS.

Clinical (excellent reference by Hui et al here)
  • The incubation period is 2-13 days (median, 5 days).
  • The illness is characterized by pneumonia, which in most cases is severe (80% require ventilatory support).
  • Typical cases begin with fever, cough, chills, sore throat, myalgia and arthralgia, followed by dyspnea and rapid progression to pneumonia.
  • Severe cases may be associated with ARDS, septic shock and multiorgan failure.
  • Fever is almost always present.
  • GI symptoms (nausea, vomiting, or diarrhea) are present in 1/3.
  • Chest imaging is always abnormal; findings include bilateral hilar infiltrates, patchy infiltrates, segmental or lobar opacities, ground glass opacities and small pleural effusions.
  • Routine laboratory abnormalities are variable.
  • Mortality rate is ~30%. In fatal cases, median time from presentation to death is 11.5 days.
  • Asymptomatic infection can occur.

Diagnostic Testing (detailed instructions by CDC here)
  • In the US, all testing is performed by public health laboratories.
  • PCR is available for BAL fluid, tracheal aspirate, pleural fluid, sputum, NP/OP swabs, NP wash/aspirate, and serum.
  • Antibody testing: acute (first week of illness), convalescent (>3 weeks after acute sample obtained).

  • No specific antiviral therapy is currently available.
  • Treatment is focused on supportive care.

Infection Control and Prevention (CDC guidance here)
  • Contact and airborne precautions are indicated for patients under investigation, and suspected and confirmed cases (see CDC case definitions here).
  • Eye protection (goggles or face shield) is specifically recommended.
  • At this time, there is no available vaccine or chemoprophylaxis.
Photo: Cynthia Goldsmith/Maureen Metcalfe/Azaibi Tamin, CDC.


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