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Infection Control in a Superspreading Event: MERS in South Korea

Amesh A. Adalja, MD, FACP, FACEP, FIDSA, July 22, 2016

While other infectious diseases have grabbed the headlines from Middle East Respiratory Syndrome (MERS), by many estimates it remains a serious threat to global health. Since its discovery in 2012, more than 1,700 cases have occurred (including 2 diagnosed in the US), resulting in more than 600 deaths. Though many of the nations involved are located on the Arabian Peninsula, a large outbreak on the Korean Peninsula is notable for many reasons. The South Korean MERS outbreak, which comprised 186 cases—38 of which were fatal—occurred in an industrial nation and underscored the role of healthcare facilities in the amplification of these events. The Annals of Internal Medicine recently published an article documenting the experience of a South Korean tertiary care center’s infection control activities during the outbreak.


2 Patients

Park and colleagues identified 2 key patients, patients A and B, in their hospital. Patient A was the first patient diagnosed with MERS in South Korea, after travel to the Arabian Peninsula, and this patient had contact with patient B in a secondary hospital prior to admission to the study hospital. In total, 45 confirmed MERS cases were admitted to the hospital, and 9,793 individuals were considered to have been exposed. 


Infection Control Activities

Several different infection control activities were undertaken by the hospital, including: contact tracing, evaluation of personal protective equipment (PPE) used by contacts, quarantine of those with close contact and inappropriate PPE use, inpatient symptom monitoring and chest radiograph screening (for those exposed to an initially missed contact, patient E, a hospital transport worker), healthcare worker cohorting, and healthcare worker symptom monitoring.

Patient A resulted in 91 exposures without appropriate PPE and 399 potential exposures, although none of these individuals developed MERS. Patient B, however, resulted in 278 people being quarantined and 617 being actively monitored. Of these individuals, 82 eventually developed MERS; only 1 of the 82 was an inpatient (with contact with patient B) detected via chest radiographic screening. 

Patient E, the hospital transport worker, was one of patient B’s exposures, and his case resulted in the quarantine of 587 people and active monitoring of 4,988. The discovery of his case resulted in a partial closure of the hospital and fever screening for all those entering the hospital. No cases were transmitted from patient E. 

Patient D was a security guard in the emergency department who was exposed to patient B, and 3 quaternary symptomatic cases stemmed from him. His infection resulted in a policy requiring all 9,000 hospital employees to report their temperatures and symptom status twice daily via an electronic system. This event also resulted in the testing of 591 asymptomatic healthcare workers who cared for MERS patients and resulted in the detection of 3 asymptomatic cases.


Optimizing Infection Control

The extensive experience of this South Korean hospital in managing a large MERS outbreak is very important for understanding the healthcare epidemiology of this virus and the best means to contain it. The fact that 82 tertiary cases originated from 1 patient leaves no doubt that this patient was a superspreader who was disproportionately contagious. Contact tracing and testing of those exposed to this patient would have identified all cases and may have prevented the 7 quaternary cases from occurring. Chest radiographic screening, fever screening, and symptom reporting seem to add little to basic contact tracing in an outbreak exclusively linked to a superspreading event. 

As hospitals around the world continue to prepare for MERS cases, it will be essential to incorporate the lesson of South Korea into their planning.



Park GE, Ko J, Peck KR, et al. Control of an outbreak of Middle East Respiratory Syndrome in a tertiary hospital in Korea. Ann Intern Med 2015;165:87-93.