title: Risk factors for transmission of Middle East respiratory syndrome coronavirus infection during the 2015 outbreak in South Korea.
abstract: Transmission heterogeneity was observed during the 2015 South Korean outbreak of Middle East respiratory syndrome coronavirus (MERS-CoV) infection. Only 22 of 186 cases transmitted the infection, and 5 super-spreading events caused 150 transmissions. We investigated the risk factors for MERS-CoV transmission.
  
  
  
  Epidemiological reports were used to classify patients as non-spreaders, spreaders (1-4 transmission), or those associated with super-spreading event (≥4 transmissions). Logistic regression analyses were used to evaluate the factors that influenced MERS-CoV transmission.
  
  
  
  Compared to non-spreaders, spreaders exhibited a longer interval from symptom onset to isolation (7 days vs. 3 days) and more frequent pre-isolation pneumonia diagnoses (68.2% vs. 17.1%). Spreaders also exhibited higher values for pre-isolation contacts (149 vs. 17.5), pre-isolation hospitalization (68.2% vs. 16.5%), and emergency room visits (50% vs. 7.3%). Spreaders exhibited lower cycle thresholds for the upE and ORF1a genes (22.7 vs. 27.2 and 23.7 vs. 27.9, respectively). Transmission was independently associated with the cycle threshold (odds ratio [OR]: 0.84, 95% confidence interval [CI]: 0.75-0.96) and pre-isolation hospitalization or emergency room visits (OR: 6.82, 95% CI: 2.06-22.84). The spreaders with ≥4 transmissions exhibited higher values for pre-isolation contacts (777 vs. 78), pre-isolation emergency room visits (100% vs. 35.3%), and doctor-shopping (100% vs. 47.1%), compared to other spreaders.
  
  
  
  These findings indicate that transmission is determined by host infectivity and the number of contacts, whereas super-spreading events were determined by the number of contacts and hospital visits. These relationships highlight the importance of rapidly enforcing infection control measures to prevent outbreaks.
authors.affiliation: Division of Epidemic Intelligence Service, Korea Centers for Disease Control and Prevention, Cheongju, Republic of Korea.
authors.forename: Seung Woo
authors.initials: SW
authors.lastname: Kim
authors.affiliation: Division of Epidemic Intelligence Service, Korea Centers for Disease Control and Prevention, Cheongju, Republic of Korea.
authors.forename: Jung Wan
authors.initials: JW
authors.lastname: Park
authors.affiliation: Division of Respiratory Viruses, Center of Infectious Disease, Korea Centers for Disease Control and Prevention, Cheongju, Republic of Korea.
authors.forename: Hee-Dong
authors.initials: HD
authors.lastname: Jung
authors.affiliation: Division of Respiratory Viruses, Center of Infectious Disease, Korea Centers for Disease Control and Prevention, Cheongju, Republic of Korea.
authors.forename: Jeong-Sun
authors.initials: JS
authors.lastname: Yang
authors.affiliation: Division of Epidemic Intelligence Service, Korea Centers for Disease Control and Prevention, Cheongju, Republic of Korea.
authors.forename: Yong-Shik
authors.initials: YS
authors.lastname: Park
authors.affiliation: Division of Epidemic Intelligence Service, Korea Centers for Disease Control and Prevention, Cheongju, Republic of Korea.
authors.forename: Changhwan
authors.initials: C
authors.lastname: Lee
authors.affiliation: Division of Epidemic Intelligence Service, Korea Centers for Disease Control and Prevention, Cheongju, Republic of Korea.
authors.forename: Kyung Min
authors.initials: KM
authors.lastname: Kim
authors.affiliation: Division of Epidemic Intelligence Service, Korea Centers for Disease Control and Prevention, Cheongju, Republic of Korea.
authors.forename: Keon-Joo
authors.initials: KJ
authors.lastname: Lee
authors.affiliation: Division of Epidemic Intelligence Service, Korea Centers for Disease Control and Prevention, Cheongju, Republic of Korea.
authors.forename: Donghyok
authors.initials: D
authors.lastname: Kwon
authors.affiliation: Center for Infectious Disease Control, Korea Centers for Disease Control and Prevention, Cheongju, Republic of Korea.
authors.forename: Young Joo
authors.initials: YJ
authors.lastname: Hur
authors.affiliation: Department of Preventive Medicine, Hanyang University Medical College, Seoul, Republic of Korea.
authors.forename: Bo Youl
authors.initials: BY
authors.lastname: Choi
authors.affiliation: Department of Cancer Control and Policy, Graduate School of Cancer Science and Policy, National Cancer Center, Goyang, Republic of Korea.
authors.forename: Moran
authors.initials: M
authors.lastname: Ki
keywords: Middle East respiratory syndrome coronavirus; South Korea; epidemiology; super-spreading event; transmission