title: Outbreaks of Middle East Respiratory Syndrome in Two Hospitals Initiated by a Single Patient in Daejeon, South Korea.
abstract: BACKGROUND
  A Middle East Respiratory Syndrome coronavirus (MERS-CoV) outbreak in South Korea in 2015 started by a single imported case and was amplified by intra- and inter-hospital transmission. We describe two hospital outbreaks of MERS-CoV infection in Daejeon caused by a single patient who was infected by the first Korean case of MERS.
  
  
  METHODS
  Demographic and clinical information involving MERS cases in the Daejeon cluster were retrospectively collected and potential contacts and exposures were assessed. The incubation periods and serial intervals were estimated. Viral RNAs were extracted from respiratory tract samples obtained from the index case, four secondary cases and one tertiary case from each hospital. The partial S2 domain of the MERS-CoV spike was sequenced.
  
  
  RESULTS
  In Daejeon, a MERS patient (the index case) was hospitalized at Hospital A in the first week of illness and was transferred to Hospital B because of pneumonia progression in the second week of illness, where he received a bronchoscopic examination and nebulizer therapy. A total of 23 secondary cases (10 in Hospital A and 13 in Hospital B) were detected among patients and caregivers who stayed on the same ward with the index case. There were no secondary cases among healthcare workers. Among close hospital contacts, the secondary attack rate was 15.8% (12/76) in Hospital A and 14.3% (10/70) in Hospital B. However, considering the exposure duration, the incidence rate was higher in Hospital B (7.7/100 exposure-days) than Hospital A (3.4/100 exposure-days). In Hospital B, the median incubation period was shorter (4.6 days vs. 10.8 days), the median time to pneumonia development was faster (3 days vs. 6 days) and mortality was higher (70% vs. 30.8%) than in Hospital A. MERS-CoV isolates from 11 cases formed a single monophyletic clade, with the closest similarity to strains from Riyadh.
  
  
  CONCLUSIONS
  Exposure to the MERS case in the late stage (2nd week) of diseases appeared to increase the risk of transmission and was associated with shorter incubation periods and rapid disease progression among those infected. Early detection and isolation of cases is critical in preventing the spread of MERS in the hospital and decreasing the disease severity among those infected.
authors.affiliation: Division of Infectious Diseases, Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea.
authors.forename: Sun Hee
authors.identifier: 0000-0001-5648-9237
authors.initials: SH
authors.lastname: Park
authors.affiliation: Division of Infectious Diseases, Department of Internal Medicine, Chungnam National University School of Medicine, Daejeon, Korea.
authors.forename: Yeon-Sook
authors.identifier: 0000-0003-1142-5488
authors.initials: YS
authors.lastname: Kim
authors.affiliation: Division of infectious disease, Department of internal medicine, Hallym Sacred Heart Hospital, Anayang, Korea.
authors.forename: Younghee
authors.identifier: 0000-0002-9034-7635
authors.initials: Y
authors.lastname: Jung
authors.affiliation: Department of Neurology, Dae-Chung Hospital, Daejeon, Korea.
authors.forename: Soo Young
authors.identifier: 0000-0001-5541-4479
authors.initials: SY
authors.lastname: Choi
authors.affiliation: Department of Microbiology and Immunology, Department of Biomedical Science, Seoul National University College of Medicine and Bundang Hospital, Seoul, Korea.
authors.forename: Nam-Hyuk
authors.identifier: 0000-0003-3673-6397
authors.initials: NH
authors.lastname: Cho
authors.affiliation: Division of Infectious Diseases, Department of Internal Medicine, College of Medicine, Chungbuk National University, Cheongju, Korea.
authors.forename: Hye Won
authors.identifier: 0000-0002-1063-8476
authors.initials: HW
authors.lastname: Jeong
authors.affiliation: Division of Infectious Diseases, Department of Internal Medicine, College of Medicine, Chungbuk National University, Cheongju, Korea.
authors.forename: Jung Yeon
authors.identifier: 0000-0002-6548-1939
authors.initials: JY
authors.lastname: Heo
authors.affiliation: Division of Infectious diseases, Department of Internal Medicine, Eulji University hospital, Daejeon, Korea.
authors.forename: Ji Hyun
authors.identifier: 0000-0001-7523-2699
authors.initials: JH
authors.lastname: Yoon
authors.affiliation: Division of Infectious diseases, Department of Internal Medicine, College of Medicine, Hallym University, Seoul, Korea.
authors.forename: Jacob
authors.identifier: 0000-0002-7041-065X
authors.initials: J
authors.lastname: Lee
authors.affiliation: Division of Infectious Diseases, Department of Internal Medicine, Chungnam National University School of Medicine, Daejeon, Korea.
authors.forename: Shinhye
authors.identifier: 0000-0002-1783-121X
authors.initials: S
authors.lastname: Cheon
authors.affiliation: Division of Infectious Diseases, Department of Internal Medicine, Chungnam National University School of Medicine, Daejeon, Korea.
authors.forename: Kyung Mok
authors.identifier: 0000-0002-3237-044X
authors.initials: KM
authors.lastname: Sohn
keywords: Daejeon; Hospital; Middle East Respiratory Syndrome coronavirus; Outbreak; South Korea; Superspreading