Current epidemiological situation of Middle East respiratory syndrome coronavirus clusters and implications for public health response in South Korea

Since May 20, 2015, when the first case of Middle East respiratory syndrome (MERS) in South Korea was confirmed, the cluster case in South Korea has grown to become the largest observed case following Saudi Arabia within the span of one month. Akin to what was observed in the Middle East, confirmed cases were infected through nosocomial transmission where the cluster is largely limited to patients, healthcare workers, and visitors to patients in healthcare facilities with confirmed cases. A major difference from the outbreaks in the Arabian Peninsula has been the large number of tertiary transmission cases in South Korea, which had reached forty cases by June 12. This observation may suggest that despite the lack of genetic mutation of Middle East respiratory syndrome coronavirus (MERS-CoV) in South Korea, the virus may be behaving differently from that of the Middle East. The higher infectiousness of 'super-spreaders' in South Korea also suggests that this assertion should be under further investigation. Suggestions of inadequate triage in emergency rooms, particularly at Samsung Medical Center which accounts for the most nosocomial infection with 60 cases, have been made by several organizations as the basis for this rapid spread. This, however, does not account for the fact that triage was impossible to implement, since the presence of MERS-CoV in South Korea was unknown during the index patient's stay at the healthcare facilities. This paper aims to identify the key factors in the amplified spread of MERS-CoV in South Korea. The first is the initial failure to confirm diagnosis promptly and to isolate the index case after confirmation of MERS in hospital and the lack of detail in tracking potential exposures in the community of the index case before isolation. The second is the early inadequate measures the Korea Centers for Disease Control and Prevention took in categorizing close contacts. Due to inconsistencies in defining what constitutes close contact, a number of cases were neglected from quarantine and were not subjected to investigation. Finally, confirmed or potential MERS patients were admitted for treatment and observation at medical facilities without adequate disease control measures or rooms, such as ventilated single rooms or airborne precaution rooms. Due to the rigid position that MERS-CoV cannot be transmitted via airborne means, infection control measures has so far neglected evidence that smaller droplets (aerosol) containing the virus can act similar to airborne agents, which may account for the widespread and rapid transmission in a emergency room and a patient's room in hospital. Although the South Korean government expects newly confirmed cases to abate in the coming few weeks, without stringent implementation of clearly defined guidelines to control further transmissions, the cessation of the current trend may continue for an extended period. Additionally, due to the high infection rate of super-spreaders in South Korea, efforts to screen for potential super-spreaders and a thorough investigation of those confirmed to be super-spreaders should be done to quickly identify source of infection, to potentially lower the number of secondary, tertiary transmissions and prevent possible quaternary transmissions.