Clinical Review

Identification and Management of Middle East Respiratory Syndrome

Fed Pract. 2015 March;32(3):12-16

References

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Transmission

MERS-CoV is thought to be of animal origin, but the mode of transmission from the animal reservoir is not known. It seems likely that some of the infections have occurred via intermittent zoonotic transmission, possibly by an environmental source.¹⁹The presence of case clusters, however, suggests that human-to-human transmission also can occur. Human-to-human transmission has occurred in individuals living with an infected person and in HCPs caring for infected patients.^20-24 The human-to-human transmission through close contact so far has been nonsustained.

It has been estimated that 75% of the reported cases are secondary, meaning that the patient acquired the MERS-CoV infection from another infected person. There is no evidence of sustained spread of MERS-CoV in community settings. The mode of human-to-human transmission has not been determined. Possible modes of transmission include droplet and contact transmission. The number of contacts infected by individuals with confirmed infections seems limited; the transmissibility, therefore, currently seems to be low.^25,26 The results of a study of the transmissibility and epidemic potential for MERS-CoV suggest that it does not yet have pandemic potential.²⁷

Bats may serve as a reservoir for MERS-CoV. However, because human contact with bats is uncommon, they are viewed as unlikely candidates for an immediate source of infection in most humans. It is possible that another animal or vector serves as an intermediate host. Camels have been proposed as a possible intermediate host, but this remains unproven. Interestingly, the MERS-CoV index patient had been caring for several ill camels in his herd; the camels had signs of respiratory illness, including nasal discharge.^11,28MERS-CoV sequences were subsequently isolated from a juvenile camel belonging to the index patient.

Symptoms

The incubation time after exposure to symptom onset ranges from 1.9 to 14.7 days (Figure). The median incubation period is 5.2 days.²¹Patients are not believed to be contagious during the incubation period. Early symptoms of human infection with MERS-CoV include fever, chills or rigors, cough, and shortness of breath. Less frequently encountered symptoms include hemoptysis, sore throat, myalgias, diarrhea, vomiting, and abdominal pain (Table 2).^{20,21,23,26,27,29} Many patients infected with MERS-CoV develop a severe lower respiratory tract illness. The patient may progress to ARDS and require intubation and mechanical ventilator support. Mechanical ventilation has been required in 72% of patients.²⁹ The median time from presentation for medical care to respiratory failure is 7 days, ranging from 3 to 11 days (Figure).

Physical Examination

The patients with MERS-CoV infection have been predominantly male and middle aged with an average age of 52 years. The clinical features depend on the severity of the illness. Some infected individuals have remained asymptomatic.²⁷Other patients have experienced mild lower respiratory illness and have not required hospitalization. However, about 40% of patients have experienced severe illness with pneumonia, respiratory insufficiency, multi-organ failure, and death. The percentage of severe illness is likely an overestimation, because patients with less severe symptoms probably are not tested for MERS-CoV. Most of the patients who have experienced a severe illness and/or death also had underlying comorbid conditions, such as diabetes mellitus, hypertension, chronic heart disease, and chronic renal disease.^23,29

Laboratory Data

As with SARS-CoV, lymphopenia has been reported in patients infected with MERS-CoV.²⁹ Other complete blood cell count abnormalities include leukopenia, lymphocytosis, thrombocytopenia, and anemia (Table 3).^23,24,26,30 Blood chemistry profiles have identified elevated aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase levels.²⁹ Some patients have experienced progressive renal failure signaled by rising serum creatinine and blood urea nitrogen levels.^11,23,24,26 Testing for disseminated intravascular coagulation and hemolysis has been positive in some patients.^20,30 Oxyhemoglobin desaturation develops in patients with severe pneumonia.

Radiographic Imaging

Chest radiographs have been abnormal in the majority of patients with MERS-CoV. The radiographic findings may be minimal to extensive, depending on the severity of illness. The reported radiographic abnormalities include increased bronchovesicular markings, airspace opacities, patchy infiltrates, interstitial changes, confluent consolidations, nodular opacities, reticular infiltrate, pleural effusion, and total opacification of lung segments and lobes. These radiographic findings may be unilateral or bilateral.²⁹

Specific Testing for MERS-CoV

The CDC recommends that lower respiratory tract specimens be collected for testing with real-time reverse-transcriptase polymerase chain reaction (rRT-PCR). The FDA has issued an emergency use authorization of the rRT-PCR assay developed by the CDC. The CDC recommends that multiple specimens from different sites in the lower respiratory system be collected at different times to increase the likelihood of detecting MERS-CoV. Acute and convalescent serum samples also should be obtained for serologic testing. Lower respiratory specimens (sputum, tracheal aspirates, and bronchoalveolar lavage fluid) are more sensitive than are upper respiratory tract samples (nasopharyngeal throat swabs and nasopharyngeal aspirates). Respiratory specimens should be collected as soon as possible after symptom onset. If negative testing is obtained from a patient with a high index of suspicion for MERS-CoV infection, then repeat testing should be performed.