How one patient spread MERS to 82 people

Micrograph of a MERS coronavirus

Almost 190 people were infected with the Middle East respiratory syndrome coronavirus (shown) in the 2015 MERS outbreak in South Korea. One superspreader, Patient 14, was responsible for nearly half of the cases.

NIAID/Flickr (CC BY 2.0)

During last year’s outbreak of Middle East respiratory syndrome in South Korea, about 20 percent of hospital patients in close contact with a single MERS case, known as Patient 14, contracted the disease, South Korean researchers found after reviewing medical records and security footage.

From May to July 2015, South Korea experienced the biggest outbreak of MERS outside of the Middle East. A few people dubbed “superspreaders” transmitted the virus to many others. Patient 14, a 35-year-old man, unwittingly transmitted the virus to 82 other people — including 33 patients, 41 visitors and eight health care workers — between May 27 and 29 while in the emergency room of Samsung Medical Center in Seoul. The man did not know he had been exposed to the virus while at another hospital.

During his time in the ER, the man came in contact with 675 patients, 218 health care workers and about 683 visitors, researchers report July 8 in The Lancet. People who spent time in the same zone of the emergency room with Patient 14 were most likely to catch the virus from him. But even people who weren’t in close contact had about a 5 percent chance of getting ill. That includes three people who overlapped with the man for a short time in the radiology suite. Even four of the 500 patients who were never in the same part of the emergency room as Patient 14 caught the virus.  

The most likely place to catch MERS from Patient 14 was the hospital’s waiting room, designated Zone II, even though people in that part of the emergency room were exposed to him for only about three hours. On average, it took about seven days after exposure to the virus for people to develop symptoms.

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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