Reproduction number

South Korea experienced an outbreak of Middle East respiratory syndrome coronavirus (MERS-CoV) with 186 confirmed cases from May to July 2015. Analysis of the reproduction number R during and after an outbreak provides information about the average number of secondary cases per infected case. Control measures lead to a reduction in R and an outbreak ends when R remains below one. Here, we provide estimates of the case reproduction number using the method by Wallinga and Teunis (2004) as implemented in the R package R0 (Figure). The analysis is based on the epidemic curve published by the World Health Organization (WHO).

Figure. Estimated case reproduction number during MERS-CoV outbreak in South Korea. The blue shaded area represents the 95% confidence interval of the estimates. The serial interval (time between onset of symptoms in a primary and secondary case) is assumed to be gamma-distributed with a mean of 12.6 days and a standard deviation of 2.8 days (Cowling et al. 2015).

The estimated reproduction number of the index case (R = 25.89, 95% CI 23-28) corroborates the epidemiological finding that the first case of the outbreak generated a disproportionate amount of secondary infections (Cowling et al. 2015). Although it is likely that the basic reproduction number R0 < 1 (Cauchemez et al. 2014), we could recently show that MERS-CoV transmission is highly overdispersed with substantial potential for superspreading events (Kucharski and Althaus 2015). The reproduction number dropped below unity for those cases whose symptoms began on 30 May 2015 or later, suggesting that the outbreak was brought under control during early June 2015.

References

Cauchemez, Simon, Christophe Fraser, Maria D Van Kerkhove, Christl A Donnelly, Steven Riley, Andrew Rambaut, Vincent Enouf, Sylvie van der Werf, and Neil M Ferguson. 2014. “Middle East respiratory syndrome coronavirus: quantification of the extent of the epidemic, surveillance biases, and transmissibility.” Lancet Infect Dis 14 (1): 50–56. doi:10.1016/S1473-3099(13)70304-9.

Cowling, B J, M Park, V J Fang, P Wu, G M Leung, and J T Wu. 2015. “Preliminary epidemiological assessment of MERS-CoV outbreak in South Korea, May to June 2015.” Euro Surveill 20 (25).

Kucharski, Adam J, and Christian L Althaus. 2015. “The role of superspreading in Middle East respiratory syndrome coronavirus (MERS-CoV) transmission.” Euro Surveill 20 (25).

Wallinga, Jacco, and Peter Teunis. 2004. “Different epidemic curves for severe acute respiratory syndrome reveal similar impacts of control measures.” Am J Epidemiol 160 (6): 509–16. doi:10.1093/aje/kwh255.