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 (R). R 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 R in nosocomial outbreaks of MERS.

METHODS

R 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 R were assumed to be six to eight days. Study parameters [R and countermeasures (d)] were estimated by fitting a model to the cumulative incidence epidemic curves using Matlab.

FINDINGS

The estimated R 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 R of 4.04, and the largest outbreak cluster in a hospital in Samsung had an R of 5.0. Assuming a six-day serial interval, the KSA outbreaks in Jeddah and Riyadh had R values of 3.9 and 1.9, respectively.

CONCLUSION

R 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.