Risk factors for transmission of Middle East respiratory syndrome coronavirus infection during the 2015 outbreak in South Korea

Seung Woo Kim; Jung Wan Park; Hee-Dong Jung; Jeong-Sun Yang; Yong-Shik Park; Changhwan Lee; Kyung Min Kim; Keon-Joo Lee; Donghyok Kwon; Young Joo Hur; Bo Youl Choi; Moran Ki

doi:10.1093/cid/ciw768

Risk factors for transmission of Middle East respiratory syndrome coronavirus infection during the 2015 outbreak in South Korea

Clin Infect Dis. 2017 Mar 1;64(5):551-557. doi: 10.1093/cid/ciw768. Epub 2016 Dec 10.

Authors

Affiliations

¹ Division of Epidemic Intelligence Service, Korea Centers for Disease Control and Prevention, Cheongju, Republic of Korea.
² Division of Respiratory Viruses, Center of Infectious Disease, Korea Centers for Disease Control and Prevention, Cheongju, Republic of Korea.
³ Center for Infectious Disease Control, Korea Centers for Disease Control and Prevention, Cheongju, Republic of Korea.
⁴ Department of Preventive Medicine, Hanyang University Medical College, Seoul, Republic of Korea.
⁵ Department of Cancer Control and Policy, Graduate School of Cancer Science and Policy, National Cancer Center, Goyang, Republic of Korea.

Abstract

Background: 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.

Methods: 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.

Results: 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.

Conclusions: 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.

Keywords: Middle East respiratory syndrome coronavirus; South Korea; epidemiology; super-spreading event; transmission.