Interhuman transmissibility of Middle East respiratory syndrome coronavirus: estimation of pandemic risk

The Lancet  
http://www.thelancet.com/journals/lancet/issue/current
Aug 24, 2013  Volume 382  Number 9893  p659 – 742

Comment
Assessing the pandemic potential of MERS-CoV
Chris T Bauch, Tamer Oraby
Preview |
The emergence in 2012 of a new disease-causing coronavirus has generated substantial concern. As of June 26, 2013, Middle East respiratory syndrome coronavirus (MERS-CoV) had caused 77 laboratory-confirmed cases and 40 deaths.1 The virus is related to the severe acute respiratory syndrome coronavirus (SARS-CoV) that emerged in 2002–03. And, as SARS-CoV had during its prepandemic stage, MERS-CoV has probably been transmitted from an unknown animal host to human beings repeatedly in the past year.2,3 Cases of human-to-human transmission have also been documented in several countries.

Interhuman transmissibility of Middle East respiratory syndrome coronavirus: estimation of pandemic risk
Romulus Breban PhD a, Julien Riou a, Prof Arnaud Fontanet PhD a b
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2813%2961492-0/abstract

Summary
Background
The new Middle East respiratory syndrome coronavirus (MERS-CoV) infection shares many clinical, epidemiological, and virological similarities with that of severe acute respiratory syndrome (SARS)-CoV. We aimed to estimate virus transmissibility and the epidemic potential of MERS-CoV, and to compare the results with similar findings obtained for prepandemic SARS.

Methods
We retrieved data for MERS-CoV clusters from the WHO summary and subsequent reports, and published descriptions of cases, and took into account 55 of the 64 laboratory-confirmed cases of MERS-CoV reported as of June 21, 2013, excluding cases notified in the previous 2 weeks. To assess the interhuman transmissibility of MERS-CoV, we used Bayesian analysis to estimate the basic reproduction number (R0) and compared it to that of prepandemic SARS. We considered two scenarios, depending on the interpretation of the MERS-CoV cluster-size data.

Results
With our most pessimistic scenario (scenario 2), we estimated MERS-CoV R0 to be 0·69 (95% CI 0·50—0·92); by contrast, the R0 for prepandemic SARS-CoV was 0·80 (0·54—1·13). Our optimistic scenario (scenario 1) yielded a MERS-CoV R0 of 0·60 (0·42—0·80). Because of recent implementation of effective contact tracing and isolation procedures, further MERS-CoV transmission data might no longer describe an entire cluster, but only secondary infections directly caused by the index patient. Hence, we calculated that, under scenario 2, eight or more secondary infections caused by the next index patient would translate into a 5% or higher chance that the revised MERS-CoV R0 would exceed 1—ie, that MERS-CoV might have pandemic potential.

Interpretation
Our analysis suggests that MERS-CoV does not yet have pandemic potential. We recommend enhanced surveillance, active contact tracing, and vigorous searches for the MERS-CoV animal hosts and transmission routes to human beings.

Funding
Agence Nationale de la Recherche (Labex Integrative Biology of Emerging Infectious Diseases), and the European Community’s Seventh Framework Programme project PREDEMICS.