Monday, October 30, 2017

Study: A Pandemic Risk Assessment Of MERS-CoV In Saudi Arabia


Although the earliest (retrospectively) identified outbreak of MERS-COV occurred at a Jordanian Hospital more than 5 years ago, as of the end of September - of 2092 cases reported worldwide -  Saudi Arabia accounted for 1721 cases (82%), including 671 related deaths (CFR of 38.9%).
MERS continues to simmer on the Arabian Peninsula, sporadically passing from camels to humans and occasionally flaring up with household or nosocomial outbreaks (sometimes involving hundreds of patients), but so far large scale community outbreaks have not occurred.
While human-to-human transmission obviously occurs, as we discussed in 2014's The Elusive R0 of MERS, the virus hasn't yet managed to adapt well enough to transmit in a sustained and efficient manner.

The R or R0 (pronounced R-naught) is the basic reproduction number; the epidemiological yardstick by which transmission of an infectious disease is measured. Essentially, the number of new cases in a susceptible population likely to arise from a single infection.
With an R0 below 1.0, a virus (as an outbreak) begins to sputter and dies out.

Above 1.0, and an outbreak can have `legs’.
Calculating the R0 is notoriously difficult, even years after an epidemic has passed. Much hinges upon the existence and subtle differences between viral strains, the accuracy of surveillance and reporting, `seasonality’, and individual host responses to the virus (i.e. number of `super spreaders’).

With the understanding that the MERS coronavirus continues to evolve over time, and what we can say about the virus's behavior a year ago not hold true tomorrow, we've a new detailed statistical analysis of MERS-COV cases reported in Saudi Arabia from May 2013 to May 2015, which appears in the November issue of the Saudi Journal Of Biological Sciences. 
While this study reported a sub-critical R0 (R: 0.85–0.97) across all regions, during the study period the central and western regions flirted with epidemic level R0 (R: 1.08–1.12) numbers.
Those without a background in statistical analysis (like myself) may find parts of this study tough sledding, but the upshot is that while apparently not quite ready for prime time, MERS-CoV wouldn't need to gain a whole lot of transmissibility to become a genuine pandemic threat.

I would note that in 2014, the R0 was described by Ziad A Memish et al. in the 2nd Advisory Board Meeting of the WHO Collaborating Center for Mass Gathering Medicine as being considerably lower than today's study, stating:
The basic reproductive rate of the virus (R0) is definitely below 1 and probably below 0.5 clearly showing that the virus has no pandemic or even local epidemic potential.
This earlier assessment came in the spring of 2014, prior to number of large nosocomial outbreaks which erupted in 2014 and 2015.  I've only included the abstract and an excerpt from the discussion. Follow the link the read it in its entirety.

A pandemic risk assessment of middle east respiratory syndrome coronavirus (MERS-CoV) in Saudi Arabia

Saleh A.Eifan, Islam Nour,  Atif Hanif, Abdelrahman M.M.Zamzam, Sameera Mohammed AlJohanic

Open Access funded by King Saud University
Under a Creative Commons license 
Since the initial emergence of Middle East respiratory syndrome coronavirus (MERS-CoV) in 2012, a high incidence rate has been observed in Saudi Arabia. This suggests that the country is at continuous risk.
The epidemic level of MERS-CoV infection was examined in Saudi Arabia by the Susceptible-Infectious-Recovered (SIR) model using a Bayesian approach for estimation of time dependent reproduction number (R) across a two-year interval (May, 2013-May, 2015) in five defined clusters, followed by sensitivity analysis of the most significant clusters. Significant MERS-CoV peaks were detected in the period between March and May of each year. Moreover, MERS-CoV infection was highlighted in western (40.8%) and central (31.9%) regions, followed by eastern region (20%).
The temporal-based Bayesian approach indicated a sub-critical epidemic in all regions in the baseline scenario (R: 0.85–0.97). However, R potential limit was exceeded in the sensitivity analysis scenario in only central and western regions (R: 1.08–1.12) that denoted epidemic level in those regions. The impact of sporadic cases was found relatively insignificant and pinpointed to the lack of zoonotic influence on MERS-CoV transmission dynamics. The results of current study would be helpful for evaluation of future progression of MERS-CoV infections, better understanding and control interventions.


Time dependent reproduction number
Sensitivity analysis
Sporadic cases

The present study reported the highest R values (Table 2) ever observed for MERS-CoV, however other studies reported R of up to 0.73 (Kucharski and Edmunds, 2015), 0.69 (Breban et al., 2013; Poletto et al., 2014) and 0.63 (Cauchemez et al., 2014).
The probable reasons for the surge of R value in the current study could be the absence of a vaccine or a treatment, besides the inefficient control measures in health care centers and hospitals as most of the observed cases were documented to be inter- and intra-hospital transmissions (Drosten et al., 2015; Oboho et al., 2015). Furthermore, Cauchemez et al. (2014) mentioned that R0 could range from 0.8 to 1.3 in the absence of the infection control measures. The results of current study are in agreement with the findings of Cauchemez et al. (2014).
A study in South Korea (Kucharski and Althaus, 2015) highlighted the risk of super-spreading events of MERS-CoV infection with relatively low basic reproductive number (R = 0.47) and should be considered as warning for future outbreak events in Saudi Arabia with the prediction of relatively higher R value.
Therefore, future tracking of infections would add value to our understanding of viral transmissibility pattern as well as contracting the CIs around the R0 value. Appropriate monitoring of cases as well as enhanced traceability procedures are important to reduce transmission rate, diminish any possible opportunity of viral adaptation to human-to-human transmission and to obtain reliable data for periodical update of the R value (Min et al., 2016).
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