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.