High reproduction number of Middle East respiratory syndrome coronavirus in nosocomial outbreaks: mathematical modelling in Saudi Arabia and South Korea

Abstract

Background: Effective countermeasures against emerging infectious diseases require an understanding of transmission rate and basic reproduction number (R₀). R₀ for severe acute respiratory syndrome is generally considered to be >1, whereas that for Middle East respiratory syndrome (MERS) is considered to be <1. However, this does not explain the large-scale outbreaks of MERS that occurred in Kingdom of Saudi Arabia (KSA) and South Korean hospitals.

Aim: To estimate R₀ in nosocomial outbreaks of MERS.

Methods: R₀ was estimated using the incidence decay with an exponential adjustment model. The KSA and Korean outbreaks were compared using a line listing of MERS cases compiled using publicly available sources. Serial intervals to estimate R₀ were assumed to be six to eight days. Study parameters [R₀ and countermeasures (d)] were estimated by fitting a model to the cumulative incidence epidemic curves using Matlab.

Findings: The estimated R₀ in Korea was 3.9 in the best-fit model, with a serial interval of six days. The first outbreak cluster in a hospital in Pyeongtaek had an R₀ of 4.04, and the largest outbreak cluster in a hospital in Samsung had an R₀ of 5.0. Assuming a six-day serial interval, the KSA outbreaks in Jeddah and Riyadh had R₀ values of 3.9 and 1.9, respectively.

Conclusion: R₀ for the nosocomial MERS outbreaks in KSA and South Korea was estimated to be in the range of 2-5, which is significantly higher than the previous estimate of <1. Therefore, more comprehensive countermeasures are needed to address these infections.

Keywords: Basic reproduction number; Epidemiology; Mathematical modelling; Middle east respiratory syndrome coronavirus; Nosocomial infection; South Korea.

Figure 1

Epidemic curves of cumulative cases by selected Middle East respiratory syndrome outbreaks in (a) Saudi Arabia (red circles, Jeddah; blue asterisks, Riyadh) and (b) South Korea (green squares, total; red circles, Pyeongtaek; blue asterisks, Samsung).

Figure 2

Best-fit reproduction number (R₀) by serial intervals of Middle East respiratory syndrome in Jeddah and Riyadh, Saudi Arabia, 2014, using the incidence decay with exponential adjustment model. Red squares, Jeddah, six days; red circles, Jeddah, seven days; red asterisks, Jeddah, eight days; blue squares, Riyadh, six days; blue circles, Riyadh, seven days; blue asterisks, Riyadh, eight days.

Figure 3

Best-fit reproduction number (R₀) by serial intervals of Middle East respiratory syndrome in South Korea, 2015, using the incidence decay with exponential adjustment model. Green squares, total, six days; green circles, total, seven days; green asterisks, total, eight days; red squares, Pyeongtaek, six days; red circles, Pyeongtaek, seven days; red asterisks, Pyeongtaek, eight days; blue squares, Samsung, six days; blue circles, Samsung, seven days; blue asterisks, Samsung, eight days.