Middle East Respiratory Syndrome Coronavirus Outbreak in the Republic of Korea, 2015

Abstract

Objectives: The outbreak of Middle East respiratory syndrome coronavirus (MERS-CoV) infection in the Republic of Korea started from the index case who developed fever after returning from the Middle East. He infected 26 cases in Hospital C, and consecutive nosocomial transmission proceeded throughout the nation. We provide an epidemiologic description of the outbreak, as of July 2015.

Methods: Epidemiological research was performed by direct interview of the confirmed patients and reviewing medical records. We also analyzed the incubation period, serial interval, the characteristics of superspreaders, and factors associated with mortality. Full genome sequence was obtained from sputum specimens of the index patient.

Results: A total of 186 confirmed patients with MERS-CoV infection across 16 hospitals were identified in the Republic of Korea. Some 44.1% of the cases were patients exposed in hospitals, 32.8% were caregivers, and 13.4% were healthcare personnel. The most common presenting symptom was fever and chills. The estimated incubation period was 6.83 days and the serial interval was 12.5 days. A total of 83.2% of the transmission events were epidemiologically linked to five superspreaders, all of whom had pneumonia at presentation and contacted hundreds of people. Older age [odds ratio (OR) = 4.86, 95% confidence interval (CI) 1.90-12.45] and underlying respiratory disease (OR = 4.90, 95% CI 1.64-14.65) were significantly associated with mortality. Phylogenetic analysis showed that the MERS-CoV of the index case clustered closest with a recent virus from Riyadh, Saudi Arabia.

Conclusion: A single imported MERS-CoV infection case imposed a huge threat to public health and safety. This highlights the importance of robust preparedness and optimal infection prevention control. The lessons learned from the current outbreak will contribute to more up-to-date guidelines and global health security.

Keywords: Middle East respiratory syndrome; coronavirus; epidemiology.

Figure 1

Epidemiologic curve of 178 confirmed cases of Middle East respiratory syndrome coronavirus (MERS-CoV) infection in the Republic of Korea, 2015. Panel A (integrated curve) depicts the overall epidemiologic curve by date of symptom onset. Red color indicates the index patient, and three main clusters (Hospital C, Hospital H, and Hospital M and N) are depicted with yellow, green, and purple, respectively. Eight cases whose date of symptom onset is uncertain or who are still under investigation are excluded. Panel B shows the epidemic curve of each of the three main clusters. Stages of transmission are expressed by different patterns. An additional case in Hospital H whose stage of transmission is uncertain is excluded.

Figure 2

Incubation period of Middle East respiratory syndrome coronavirus (MERS-CoV) infection outbreak in the Republic of Korea, 2015. Panel A shows the density estimation of incubation periods with gamma distribution. Panel B shows the empirical cumulative density estimation of incubation period.

Figure 3

Serial interval of Middle East respiratory syndrome coronavirus (MERS-CoV) infection outbreak in the Republic of Korea, 2015. Panel A shows the density estimation of serial intervals using gamma distribution. Panel B shows the empirical cumulative density estimation of serial intervals.

Figure 4

Transmission map of 182 confirmed cases of Middle East respiratory syndrome coronavirus (MERS-CoV) infection in the Republic of Korea. The numbers within the red circles are identifiers of notable patients who caused succeeding MERS-CoV infection. The site and the duration of exposure by these patients are indicated in colored boxes. Gray boxes depict the time periods that new cases occurred by date of symptom onset at each site. Black arrows represent how each spreader moved to the next site of transmission. The transmission route of Patient 119 is uncertain. Four cases still under investigation are excluded.

Figure 5

Evolutionary history of the Middle East respiratory syndrome coronavirus (MERS-CoV). A phylogenetic tree was constructed using RAxML. The scale bar shows evolutionary distance inferred by RAxML algorithm. The MERS-CoV in the Republic of Korea outbreak is indicated by a red cycle. Support for the ML phylogenetic trees was evaluated using 1,000 bootstrap replicates. Note numbers represent % bootstrap replicates >70%.