Super-Spreader Key to MERS Outbreak

Norra MacReady

July 11, 2016

The 2015 outbreak of Middle East respiratory syndrome coronavirus (MERS-CoV) in South Korea can be traced largely back to one "super-spreader," the authors of a new study report.

The high transmission after single-patient exposure suggests the virus may be more transmissible than previously thought, they write in an article published online July 8 in the Lancet.

The findings should serve "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."

Super-spreaders are patients who, possibly because of increased viral load or heavy nasal secretions, "can cause large outbreaks through several modes of transmission," Sun Young Cho, MD, from the Division of Infectious Diseases, Department of Internal Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea, and colleagues write.

In this case, the patient's movement through the hospital may also have been a factor.

MERS-CoV was initially thought to have relatively low transmissibility, but in 2013, a MERS-CoV outbreak in Saudi Arabia was attributed to a super-spreader. (Such super-spreaders were also identified during the severe acute respiratory syndrome coronavirus outbreaks.)

The South Korean MERS-CoV outbreak, which involved 186 patients, occurred between May and July 2015. Patient 1 was a Korean businessman who had traveled to the Middle East. Upon returning to South Korea, he fell ill and sought care at several facilities before visiting the emergency room at Samsung Hospital in Seoul on May 17, 2015, and again on May 18, when he was diagnosed and admitted.

Although none of the 285 patients and 193 healthcare workers who came in contact with patient 1 at Samsung Hospital contracted MERS-CoV, he had transmitted the virus to 28 people who had contact with him at previous hospitals.

One of those people, patient 14, developed MERS-CoV symptoms on May 20, 2015, and on May 27 went to the Samsung Hospital emergency department, where he stayed until May 29, when his illness was diagnosed and he was placed in isolation.

The emergency department at Samsung Hospital is divided into different zones, with seating areas for stable patients, an area for seriously ill patients who require observation and a bed, and an area for patients being admitted. Between May 27 and May 29, patient 14 stayed in each of these areas for 10 to 25 hours. He also visited the radiology suite and the corridor outside the emergency room.

Using electronic medical records and security video footage, the authors identified every patient who had had contact with patient 14. They then placed each patient into one of three groups on the basis of their maximum exposure: group A, close contacts, people in the same zone as patient 14; group B, people who had had a time overlap with patient 14 in the registration area or radiology suite; and group C, people who had been in different zones. They also interviewed healthcare workers and visitors who might have had contact with patient 14.

The authors identified 675 patients, 683 visitors, and 218 workers who met the criteria. Between May 30 and June 23, 2015, 82 cases of MERS-CoV infection were confirmed in this population: 33 (40%) in patients, 41 (50%) in visitors, and 8 (10%) in healthcare workers.

The median incubation period was 7 days (range, 2 - 17 days; interquartile range [IQR], 5 - 10 days), but was significantly shorter in group A (median, 5 days; IQR, 4 - 8 days) than group C (median, 11 days; IQR, 6 - 12 days; P < .0001).

Proximity was the main risk factor for transmission. Whereas the overall infection rate among the patients was 4%, it was significantly higher among patients in group A, at 20%, compared with 5% in group B, and 1% in group C.

Among healthcare workers, the overall infection rate was 2%. After adjustment for age, sex, and underlying disease, presence in group A was associated with the highest risk for infection: Compared with those in group B, healthcare workers in group A had an odds ratio (OR) for infection of 4.32 (95% confidence interval [CI], 1.22 - 24.49; P = .016; compared with those in group C, the group A OR was 25.59 [95% CI, 8.22 - 111.39; P < .0001]).

After adjusting for age, sex, underlying disease, and exposure time, the OR of infection was similar in the seating area compared with the area with beds for seriously ill patients (OR, 0.91; 95% CI, 0.23 - 3.83; P = 1.00), but much higher for those areas compared with the area for patients being admitted (OR, 5.62; 95% CI, 1.25 - 36.84; P = .019).

"Among patients who stayed in various locations, those who overlapped with Patient 14 at the radiology suite or registration area had higher attack rates (5%) than the rest of the patients (1%), suggesting that transmission might occur by even brief exposures to recently contaminated objects or encounters with individuals carrying a super-spreader," they write.

In an accompanying comment about the study, David S. Hui, MD, from the Department of Medicine and Therapeutics and Stanley Ho Center for Emerging Infectious Diseases, The Chinese University of Hong Kong, notes that several factors facilitated transmission from both patient 1 and patient 14, including "failure to implement strict isolation of patients and quarantine of contacts at the first outbreak hospital...poor communication and knowledge of patient movement between hospitals, overcrowding in the emergency room, inadequate ventilation with only three air changes per [hour], and limited availability of isolation rooms in the emergency room."

The practice by many Korean patients of "seeking care at different health-care facilities (so-called doctor shopping), as in the cases of Patients 1 and 14, and having friends and family members to stay with patients as caregivers at already overcrowded healthcare facilities" also may have contributed.

The authors and editorialist have disclosed no relevant financial relationships.

Lancet. Published online July 8, 2016. Article abstract, Comment extract

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