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New Information on MERS Highlights Need for Infection Control and Broad Case Definition

By Amesh A. Adalja, MD, FACP, and Eric Toner, MD, June 20, 2013

Two major recent developments in the evolving scientific and clinical understanding of Middle East Respiratory Syndrome coronavirus (MERS-CoV) reinforce the fact that this highly lethal virus is capable of wide dissemination, especially within hospitals. As of today, the official WHO case count stands at 64, with 38 deaths.

Retrospective Investigation of Hospital Cluster in Jordan

In April 2012, a cluster (12 or more cases) of then unexplained respiratory illnesses occurred in a Jordanian hospital. After MERS-CoV was identified in September 2012 from cases in Saudi Arabia, retrospective PCR testing was performed on stored Jordanian specimens, and it revealed that 2 cases (both fatal) from the April outbreak in Jordan resulted from MERS-CoV. Because many more individuals in Jordan had been ill or exposed, 124 additional stored samples were tested using a recently developed serologic assay. As a result, 8 more cases of MERS were confirmed, bringing the total case count in Jordan to 10. Notably, the 8 additional cases are somewhat different from other MERS cases in that most did not have predisposing conditions, and one was an asymptomatic household contact.1 If the cases in Jordan cases are eventually added to the official case counts, the worldwide total will rise to 72 cases with 38 deaths.

Saudi Hospital Cluster Resulted from Nosocomial Spread

From April to May 2013, the eastern Saudi Arabian province of Al-Ahsa reported 23 cases of MERS, 15 of which were fatal, and 21 of which were contracted in a hospital’s hemodialysis unit and ICU, both of which had open-ward designs. A description of the Saudi experience, just published in The New England Journal of Medicine, provides important data on the clinical presentation and the nosocomial spread of MERS. In particular, Assiri and colleagues note that most of the cases can be traced to the hospital’s open-ward style hemodialysis unit before infection control measures were initiated or from the open ICU, where aerosolized medication, CPR, and mechanical ventilation were administered. Most of the hospital infections occurred among patients; only 2 healthcare workers had laboratory-confirmed infection with MERS-CoV.2 The outbreak ceased after introduction of basic infection control measures: standard-, contact-, and droplet-precautions; masks for patients; and exclusion of new suspected MERS patients from the units.

Regarding clinical presentation/characteristics, the authors report that fever and cough were present in most cases, and 35% presented with vomiting and/or diarrhea. As has been described in other reports, many case patients had underlying diseases such as renal failure and diabetes. Importantly, at presentation, 70% of patients had a normal oxygen saturation level (Sp02) when breathing room air and 13% had a normal chest x-ray.2

Preparing for and Preventing Spread of MERS-CoV

These new reports of large hospital-based outbreaks underscore the risk that MERS poses for unprepared healthcare facilities. Just as with SARS CoV—albeit on a smaller scale so far—MERS-CoV has demonstrated its ability to spread among hospitalized patients in the absence of adequate infection control. With its relatively long incubation period and serial interval (up to 2 weeks in some cases) combined with the realities of modern air travel, continued exportation of MERS to other parts of the world is a real concern. Moreover, it is entirely possible that some cases will be missed, given the possibility of mild or asymptomatic cases and a clinical presentation in which oxygen saturation and CXR may initially be normal in some patients. Testing might not be performed on mild or atypical (but possibly contagious) cases if only severe cases with typical presentations are recognized.

We caution clinicians and public health authorities to not be overly rigid in applying strict case definitions to possible MERS patients who meet some but not all the criteria. Clinicians should routinely ask about travel histories in patients with febrile, respiratory, or GI illnesses. If a patient has recently travelled to or been in contact with someone who has travelled to a region where MERS has been found, diagnostic testing should be considered. Furthermore, we strongly urge hospitals to pay better attention to existing guidelines for infection control. SARS and now apparently MERS can be controlled by strict application of basic infection control measures.


  1. CDC expert reports some anomalies in Jordan MERS cases. CIDRAP. June 19, 2013. Accessed June 20, 2013.
  2. Assiri A, McGeer A, Perl TM, et al. Hospital outbreak of Middle East Respiratory Syndrome Coronavirus. N Engl J Med. 2013; Accessed June 20, 2013.