The first case of Middle East respiratory syndrome coronavirus (MERS-CoV) was reported in 2012.¹ Over the past 3 years, sporadic travel-associated importations occurred to countries in Europe, North Africa and Asia, and cases continued to smoulder in Saudi Arabia,² but the risk assessment by most experts was that MERS-CoV was a low risk for causing a pandemic.^3,4 With a reproductive number (Ro) estimated at close to 1.0 by some experts, MERS-CoV was considered unlikely to propagate enough to cause a large outbreak.⁵ However, before 2014, a similar argument could have been made for the likelihood of a large outbreak of Ebola—in over four decades, Ebola had never caused more than several hundred cases at worst. It appears that the disclaimer made for financial investments applies equally well to emerging infections—past experience is no guarantee of future performance.

On 4 May 2015, a 68-year-old Korean man returned from travel in the Middle East. He became symptomatic on 11 May and sought medical attention on 12 May. He was admitted and discharged, then re-admitted at a second hospital where the diagnosis of MERS-CoV infection was confirmed on 20 May.⁶ In the week before diagnosis, this index case was not suspected to have MERS-CoV and, therefore, his caregivers did not use appropriate isolation precautions and personal protective equipment. As a result of this critical …