Middle East respiratory syndrome (MERS) in Asia: lessons gleaned from the South Korean outbreak

The first case of Middle East respiratory syndrome coronavirus (MERS-CoV) was reported in 2012. 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, but the risk assessment by most experts was that MERS-CoV was a low risk for causing a pandemic. 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. 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. 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 lapse, South Korea experienced a large outbreak and is now the country with the second largest number of MERS-CoV cases in the world, after Saudi Arabia. As of 23 July 2015, this outbreak stands at 186 cases, with 36 deaths and a case fatality rate of 19%; South Korea appears to be on track to declare the outbreak over by August 2015 after completing two incubation periods without new cases. Over 16 000 individuals had to be quarantined for potential exposure and over 30 healthcare facilities had to undergo investigations for possible MERS-CoV transmission. This outbreak caused considerable anxiety in Asia because one of the second generation cases travelled to China (Guangzhou and Hong Kong), requiring strenuous contact tracing efforts of fellow airplane passengers and others exposed to the patient. As a result, countries around the region issued travel warnings, stepped up screening efforts and activated thermal scanners for incoming passengers from South Korea. This outbreak took a substantial toll on South Korea, economically and politically, in addition to the human impact. The question still remains: why did this MERS-CoV outbreak occur in South Korea when the preceding 3 years had seen multiple other importations that did not result in an outbreak, even in less developed countries? AWHO team, led by Dr Keiji Fukuda, was dispatched to investigate this outbreak. Initial concerns, about viral mutation resulting in a more transmissible pathogen were not borne out by viral sequencing data. The concept of ‘super-spreaders’ was again mooted. For severe acute respiratory syndrome (SARS) veterans watching this outbreak unfold, a sense of deja vu prevailed. These events reinforced five key observations and learning points (Box 1).