A recent outbreak of Middle East Respiratory Syndrome (MERS) virus at a South Korean hospital was transmitted from a single super-spreader patient in an overcrowded emergency department to 82 individuals during the course of 3 days, according to study results  published in The Lancet.

Researchers at the Samsung Medical Center in Seoul conducted a retrospective investigation of the outbreak, which included a review of closed-circuit security video footage and electronic medical records.

An outbreak of MERS coronavirus (MERS-CoV) occurred in South Korea between May 2015 and July 2015, with 186 cases confirmed within 2 months. The index patient, identified as Patient 1, was a man 68 years of age who had traveled to Bahrain, the United Arab Emirates, Saudi Arabia, and Qatar between April 18, 2015 and May 3, 2015 before returning to South Korea.


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Patient 1 visited the Samsung Medical Center on May 17, 2015 and was isolated on May 18, 2015 under the suspicion of MERS. He was diagnosed with MERS on May 20, but before he arrived at the medical center, the patient had already transmitted the virus to several individuals at other hospitals, including the man he shared a ward with known as Patient 14. Patient 14, aged 35 years, was admitted to Samsung Medical Center on May 17, 2015. However, there was no information for this patient regarding possible exposure to MERS-CoV, which led to the hospital outbreak.

“The difference of transmissibility between these 2 individuals could be caused by a combination of factors such as the time from onset of disease, clinical symptoms, duration of contact exposure, pattern of behavior inside and near the emergency room, and kinetics of viral shedding,” the researchers wrote.

The researchers estimated that 1576 individuals were exposed to Patient 14 in the emergency department. Those infected included 33 patients, 8 healthcare workers, and 41 visitors, between May 27, 2015 and May 29, 2015.

Individuals were classified into groups depending on their proximity to Patient 14. Patients who were in the same zone of the emergency department as Patient 14 had the highest risk of infection (20%), compared with the individuals who encountered Patient 14 in the registration area or the radiology suite of the emergency department (5%). The risk of infection was 2% among healthcare workers and 6% among visitors.

The overall average incubation period was 7 days, but only 5 days for patients who were located closest to Patient 14 compared with 11 days for patients who were located farther away.

There were no confirmed cases of patients or visitors who visited the emergency department on May 29, after Patient 14 had been isolated.

Patient 1 was in contact with 285 other patients and 193 healthcare workers, but no further transmissions occurred at the hospital before the patient’s isolation on May 18. However, the patient had previously infected 28 other patients in another hospital.

“Emergency preparedness and vigilance are crucial to the prevention of further large outbreaks in the future,” the researchers concluded. “Our report serves as an international alarm that preparedness in hospitals, laboratories, and governmental agencies is the key not only for MERS-CoV infections but also for other new emerging infectious diseases.”

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Reference

1. Cho SY, Kang JM, Ha YE, et al. MERS-CoV outbreak following a single patient exposure in an emergency room in South Korea: an epidemiological outbreak study. Lancet. 2016; doi: 10.1016/S0140-6736(16)30623-7.