Thursday, September 11, 2014

Eurosurveillance: Stopping Ebola & R0 Calculations


# 9065



In somewhat the same vein as my earlier post Conventional Wisdom And Epidemic Disease Spread, the Journal Eurosurveillance has published an editorial and a paper on the transmissibility of the West African Ebola outbreak.  


Both paint a grim picture of what is to come if sufficient efforts are not mounted to stop this outbreak.


The editorial by A  J Kucharski  and  P Piot of the London School of Hygiene & Tropical Medicine, London warns that some of the near-apocalyptic case projections we discussed earlier today are not out of the question.  A couple of excerpts, but follow the link to read the article in its entirety.


Eurosurveillance, Volume 19, Issue 36, 11 September 2014


Containing Ebola virus infection in West Africa

A J Kucharski 1, P Piot1

Ebola virus disease (EVD) is leaving a mark deeper and wider than ever before. The current outbreak now spans five countries in West Africa – Guinea, Liberia, Nigeria, Senegal and Sierra Leone – with over 4,200 cases and 2,200 deaths reported to the World Health Organization (WHO) as of 6 September 2014 (Figure 1) [1]. Unfortunately, with many cases either not reported or yet to show symptoms, the true number of infections is likely to be considerably higher. The first countries affected were among the world’s poorest, areas where long periods of civil wars have battered health services and eroded public trust. As a result, the outbreak has spread to other countries, and continues to expand. What began as a local problem has turned into an international crisis.


Ebola cannot be ignored in the hope it will burn itself out. It is true that outbreaks of acute infections will generally decline once a large number people have been infected, because there are no longer enough susceptible individuals to sustain transmission. But if Ebola indeed has a reproduction number of 2 in some locations as described by Nishiura et al. [8], the susceptible pool – which likely includes most individuals – would have to shrink by at least half before the outbreak declined of its own accord [17]. Given the vast populations in affected areas and the disease’s high fatality rate, this is clearly not an acceptable scenario.

(Continue . . . )

The second study looks at the R0 of this outbreak, something we’ve looked at previously in PLoS Currents: Calculating An R0 For Ebola. As a refresher, the R0 (pronounced R-nought) or Basic Reproductive Number is 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’.


Like the earlier study, today’s report finds the R0 of the Ebola outbreak to be well over 1.0. More than enough to sustain the epidemic.



Eurosurveillance, Volume 19, Issue 36, 11 September 2014

Rapid communications

Early transmission dynamics of Ebola virus disease (EVD), West Africa, March to August 2014

H Nishiura ()1, G Chowell2,3

Date of submission: 23 August 2014

The effective reproduction number, Rt, of Ebola virus disease was estimated using country-specific data reported from Guinea, Liberia and Sierra Leone to the World Health Organization from March to August, 2014. Rt for the three countries lies consistently above 1.0 since June 2014. Country-specific Rt for Liberia and Sierra Leone have lied between 1.0 and 2.0. Rt<2 indicate that control could be attained by preventing over half of the secondary transmissions per primary case.

(continue . . . )


1 comment:

Iaato said...

Thanks for your very current reports. Given the messiness and contagious nature of this disease, as it spreads and overwhelms health systems, R0 could increase, depending on the country. The more this spreads, the less we'll be able to cope, and the more it will spread, especially global transmission via airplane.

The bottom line or Liebig's minimum ( the limiting factor that controls rate of growth) for this disease is isolation nursing care and beds. Even in first world countries, or perhaps especially in first world countries, our just-in-time system has no slack in beds or nursing care, and high standards of care demand intensive use of personnel in isolation care.