Middle East respiratory syndrome (MERS): A new zoonotic viral pneumonia

Cunha, Cheston B; Opal, Steven M

The median incubation period for human-to-human transmission is approximately 5 d (range 1.9-14.7 d). The median time from onset of MERS to hospitalization is approximately 4 d. The median time from onset of illness to ICU admission is approximately 5 d. The median onset to death is approximately 12 d. The median duration of mechanical ventilation is 16 d and the median duration of an ICU stay is 30 d. The mortality for MERS patients in the ICU for 90 d is 58%. 5, 17, 18 Patients with MERS present as an influenza-like illness (ILI). SARS and MERS have some features in common, i.e., fever with chills, headache, and dry cough, but SARS was a biphasic illness, and not an ILI. 5 Some patients are asymptomatic or present with mild respiratory symptoms without fever or diarrhea before developing MERS. 19 Typically, MERS rapidly progresses to viral pneumonia about a week after the onset of the infection. As with influenza, some patients report a sore throat. The chest radiograph is abnormal in patients ill enough to be hospitalized. A unilateral basilar infiltrate is common initially resembling a lobar/segmental bacterial pneumonia. More commonly, MERS presents with bilateral interstitial infiltrates which may be somewhat ovoid or nodular in appearance. 5 Small pleural effusions are not uncommon. Consolidation may occur but cavitation is not a feature of MERS pneumonia. 17 Bacterial co-infection does not occur with MERS. 15 Patients rapidly progress to ARDS (small lung volumes without cardiomegaly) with severe hypoxemia and bilateral interstitial infiltrates as with severe pandemic influenza (H 1 N 1 ) or severe avian influenza (H 7 N 9 ). Death is from hypoxemia from acute respiratory failure and or ARDS. As with any patient intubated with respiratory failure on prolonged ventilatory support, nosocomial pneumonia (not co-infection) may complicate MERS. 5 Non-specific laboratory tests with MERS include leukopenia, relative lymphopenia, and thrombocytopenia. Thrombocytopenia occurs less frequently than in influenza pneumonia where it is a near universal finding in hospitalized adults. Serum transaminases are often mildly to moderately elevated in hospitalized patients with MERS. MERS-CoV is present in blood, urine, and feces, but the diagnosis is made by demonstrating the SARS-CoV in lower respiratory secretions by RT PCR. In hospitalized patients with severe viral pneumonia, the likelihood of recovery of MERS is highest in lower respiratory tract specimen secretions rather than nasal swabs. 5, 17, 18 Without a travel history linking the patient to the Arabian peninsula or a known MERS case, the clinical presentation may be indistinguishable from other severe viral pneumonias. 17 The clinical feature which distinguishes MERS from influenza is the relatively high frequency of renal involvement, i.e., renal failure with MERS 5,14-16 ( Table 1) .