Coronaviruses are large enveloped single-stranded RNA viruses than can infect and cause disease in many animal species, including human beings, bats, mice, birds, dogs, pigs and cattle. In humans, five respiratory coronaviruses causing common cold (229E and OC43), upper respiratory tract infections (NL63) or pneumonia (HKU1 and SARS) have been described.
In September 2012, a novel human coronavirus was identified in two patients with severe respiratory disease. This new virus is genetically closely related to coronaviruses from various bat species in Africa and Eurasia. All reported cases have been linked directly or indirectly to one of four countries: Saudi Arabia, Qatar, Jordan and the United Arab Emirates. To date, no cases have been reported in the United States. Most illnesses have occurred in individuals aged 24 years and older; only two infected children (aged 2 and 14 years) have been reported.
Symptoms begin with flu-like illness (ie, high fever, rigors and malaise) followed by cough, myalgias and headache. No upper respiratory symptoms such as sore throat, nasal discharge or nasal congestion have been reported. Productive cough with purulent blood-streaked sputum was observed. Respiratory distress becomes progressive with severe hypoxemia. Chest X-rays show extensive consolidation of the parenchyma. Many of the patients have had gastrointestinal symptoms as well, including anorexia, abdominal pain and diarrhea.
The virus has infected 61 patients (as of June 15) with a mortality rate of 56%. It is not as easily transmissible as SARS, and many of the patients with severe disease have been immunosuppressed. The virus is more easily isolated from secretions obtained from the lower respiratory tract than the upper respiratory tract. Peak excretion of the virus from the lower respiratory tract appears to occur after 1 week of illness. Transmission is probably by respiratory droplet with an incubation period that may be as long as 9 to 12 days. There is also possible transmission via the fecal-oral route.
This outbreak is a fascinating phenomenon that prompts recollection of the SARS epidemic in 2002. Person-to-person transmission with this new virus is much less likely than with SARS. Currently, it appears that the mortality is very high with MERS coronavirus. However, until a serologic test is available that may allow detection of milder episodes of infection, the current numbers may be misleading.
These cases are a reminder of the importance of using standard, contact and airborne precautions when there is a possible viral infection of the upper or lower respiratory tract. When excellent infection control practices have been implemented, there have been no secondary cases of MERS coronavirus infection.
Ellen R. Wald, MD
Professor and Chair, Department of Pediatrics
University of Wisconsin School of Medicine and Public Health
Disclosures: Wald reports no relevant financial disclosures.