Approximately one year ago, a novel coronavirus, the Middle East respiratory syndrome coronavirus (MERS-CoV), was first identified as the causative agent of a lethal pneumonia in several patients in the Middle East. As of July 10, 2013, a total of 80 cases have been identified in the Middle East (Saudi Arabia, Jordan, Qatar and the United Arab Emirates), Europe (UK, France, Italy, and Germany) and North Africa (Tunisia), with a case fatality rate of 56%. Since this coronavirus is a close relative of the virus that caused the severe acute respiratory syndrome (SARS), a short-lived but alarming epidemic in 2002-2003 that resulted in approximately 8,000 cases and 800 deaths, governmental, public health, clinical and laboratory authorities all mobilised rapidly to respond to the new virus outbreak. Soon after the identification of MERS-CoV, information about its genomic sequence and organisation, species tropism, and host-cell receptor (dipeptidyl peptidase 4) was published. These initial studies did not identify the source of this newly identified virus, nor did they reveal whether MERS-CoV could be transmitted from human to human, a requirement for designation as an epidemic disease.

In a recent study in the New England Journal of Medicine,¹ Assiri et al describe the largest outbreak of MERS-CoV infection thus far, showing that the virus is transmitted from human to human. This outbreak occurred in several hospitals in the governorate of Al-Hasa in eastern Saudi Arabia, with transmission probably occurring in dialysis units, intensive care units and wards. Most patients had underlying diseases, with a remarkable number (17 of 23) having diabetes. In addition to showing that human-to-human transmission occurred frequently, the relatively large number of patients infected in this outbreak made it possible to define characteristics of the infection, such as the incubation time (5.2 days) and the serial interval (7.6 days). As seen in the SARS epidemic, there was variability in the numbers of patients infected by each index patient, with one patient transmitting virus to seven contacts; superspreading events, in which a few patients infected large numbers of contacts, were critical factors in SARS reaching epidemic proportions. 

The Assiri study shows that MERS-CoV has the potential to spread widely within healthcare settings. Patients with diabetes or chronic renal failure appear to be at especially high risk for severe MERS-CoV infection. Acute renal failure developed in several patients with the infection, possibly reflecting a high level of dipeptidyl peptidase 4-receptor expression in the kidney. 

Although human-to-human transmission has been demonstrated, an epidemic is not a certainty, since a first set of statistical analyses – performed with the use of all the available data on human-to-human transmission, including those in the study by Assiri et al – suggests that MERS-CoV does not now have pandemic potential. Thus, in the absence of further adaptation or repeated introduction from community sources, widespread infection may not develop. The prevention of future spread of the epidemic will require careful surveillance and testing of patients with pneumonia living in the Middle East or with a history of recent travel to affected regions. It is also essential to determine the prevalence of MERS-CoV seropositivity in human and animal populations in Saudi Arabia and elsewhere in the Middle East to establish the likelihood of an epidemic. This information is critical for an effective public health response. Obtaining these data is dependent on the generation of a validated serologic assay, which is not currently available.

Reference

1. Assiri A, McGeer A, Perl TM et al. Hospital outbreak of Middle East respiratory syndrome coronavirus. N Engl J Med 2013; 369: 407-416