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

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.