Ebola outbreak to get worse, says WHO

Behind the Headlines

Wednesday September 24 2014

The Ebola virus is named after the river near where cases were first reported

The Ebola virus – tiny but deadly

“Ebola infections will treble to 20,000 by November,” BBC News reports, following the publication of an analysis of the current epidemic by the World Health Organization (WHO).

The report assesses what is known about the spread and devastating impact of the Ebola outbreak to date, while also predicting what may happen in the near future.

The study used data from five West African countries affected by the ongoing Ebola outbreak to estimate that around 70% of people infected (probable or confirmed cases) died from it up to September 14 2014. It states that the disease is likely to continue to spread, unless there are rapid improvements in disease control measures. Without this, it estimates that 20,000 people could be infected by the end of November  an almost quadrupling of the numbers affected up to mid-September (around 4,500). 

This report appears to be based on the pragmatic data available during the outbreak, meaning that it will be prone to some error. However, given the circumstances, it is unlikely that substantially better data will be available any time soon.

However, the analysis did offer a glimmer of hope. It discussed how new cases of the disease may be reduced within two to three weeks of introducing disease control measures, such as

  • improvements in contact tracing
  • adequate case isolation
  • increased capacity for clinical management
  • safe burials
  • greater community engagement
  • support from international partners


Long-term predications

The US’s Center for Disease Control (CDC) has published a related study, estimating what the likely long-term outcome of the current Ebola epidemic will be.


It estimates that unless the interventions described above are carried out, there is the distinct possibility that more than 1 million people could be infected by the beginning of 2015, as the disease spreads almost exponentially.


An epidemic of this scale increases the chance that the disease could spread to other areas of the world.

Where did the story come from?

The study was carried out by members of the WHO Ebola Response Team and was funded by numerous sources, including: the Medical Research Council, the Bill and Melinda Gates Foundation, the Models of Infectious Disease Agent Study of the National Institute of General Medical Sciences (National Institutes of Health), the Health Protection Research Units of the National Institute for Health Research, European Union PREDEMICS consortium, Wellcome Trust and Fogarty International Center.

The study was published in The New England Journal of Medicine  a peer-reviewed medical journal – on an open access basis, so it is free to read online.

BBC News covered the research accurately.

The Mail Online and The Independent covered reports by both the WHO and CDC. Again, their reporting reflected the underlying research.


What kind of research was this?

This was a cross-sectional study assessing cases of Ebola virus disease (EVD, or Ebola for short) in five West African countries.

As of September 14 2014, a total of 4,507 confirmed and probable cases of Ebola, as well as 2,296 deaths from the virus, had been reported from five countries in West Africa: Guinea, Liberia, Nigeria, Senegal and Sierra Leone.

Smaller Ebola outbreaks have happened before, but the current outbreak is far larger than all previous epidemics combined. This latest study aimed to gather information from the five countries most affected, to gain an insight into the severity of the outbreak and predict the future course of the epidemic.


What did the research involve?

By September 14 2014, a total of 4,507 probable and confirmed cases, as well as 2,296 deaths, from Ebola (Zaire species) had been reported to the WHO from five West African countries – Guinea, Liberia, Nigeria, Senegal and Sierra Leone. The latest WHO report analysed a detailed subset of data on 3,343 confirmed and 667 probable Ebola cases from these countries.

Ebola outbreak data was collected during surveillance and response activities for Ebola in the respective countries during the outbreak.

Clinical and demographic data were collected from probable and confirmed cases using a standard Ebola case investigation form. Additional information on the outbreak was gathered from informal case reports, by data from diagnostic laboratories and from burial records. The data recorded for each Ebola case included the district of residence, the district in which the disease was reported, the patient’s age, sex, signs and symptoms, the date of symptom onset and of case detection, the name of the hospital, the date of hospitalisation, and the date of death or discharge.

The analysis focused on describing epidemiological characteristics of the outbreak using the individual confirmed and probable cases records for each country. Results related to suspected cases were demoted to an appendix, as they were less reliable.


What were the basic results?

The main characteristics of the Ebola outbreak are:

  • The majority of patients are 15 to 44 years of age (49.9% male).
  • The estimated chance of dying from Ebola is 70.8% (95% confidence interval [CI], 69 to 73) among persons with known infection. This was very similar across the different countries.
  • The average delay between being infected with the Ebola virus and displaying symptoms is 11.4 days. The course of infection, including signs and symptoms, is similar to that reported in previous Ebola outbreaks.
  • The estimated current reproduction numbers are: 1.81 (95% CI, 1.60 to 2.03) for Guinea, 1.51 (95% CI, 1.41 to 1.60) for Liberia and 1.38 (95% CI, 1.27 to 1.51) for Sierra Leone. The reproduction number is the number of new cases one existing case generates over the time they are infected with the virus. For example, the Guinea rate of 1.81 means that, on average, every person with Ebola infects just under 2 new people with the disease. Reproduction numbers greater than 1 indicate the disease is spreading in a population, with a higher number indicating that the spread is faster. A reproduction rate of above 2 is particularly concerning, as it means that an infection is now spreading exponentially (1 person infects 2; 2 infects 4, 4 infects 8, and so on).
  • The corresponding doubling times – the time it takes for the disease incidence to double  was 15.7 days (95% CI, 12.9 to 20.3) for Guinea, 23.6 days (95% CI, 20.2 to 28.2) for Liberia and 30.2 days (95% CI, 23.6 to 42.3) for Sierra Leone.
  • On the basis of the initial periods of exponential growth, the estimated basic reproduction numbers for the future are: 1.71 (95% CI, 1.44 to 2.01) for Guinea, 1.83 (95% CI, 1.72 to 1.94) for Liberia and 2.02 (95% CI, 1.79 to 2.26) for Sierra Leone.
  • Assuming no change in the control measures for this epidemic, by November 2 2014, the cumulative reported numbers of confirmed and probable cases are predicted to be 5,740 in Guinea, 9,890 in Liberia and 5,000 in Sierra Leone – exceeding 20,000 in total.


How did the researchers interpret the results?

The Ebola Response Team were clear in their conclusions, saying their findings “indicate that without drastic improvements in control measures, the numbers of cases of and deaths from EVD [Ebola virus disease] are expected to continue increasing from hundreds to thousands per week in the coming months.”



This latest WHO study used data from five West African countries affected by the ongoing Ebola outbreak to estimate that around 70% of people infected (probable or confirmed cases) died from it up to September 14 2014. They found the disease is spreading, and is likely to continue spreading unless there are improvements in disease control measures. This means that if the status quo is maintained, they predict that the outbreak will get worse, rather than better.

This report appears to be based on the pragmatic data available during the outbreak. Such data is always prone to some error, as record keeping and case detection is not 100% accurate, particularly in resource-poor countries or districts. The WHO team thinks their estimates of the disease underestimate the size of the issue, as not all cases will have been detected by their methods, and case records were often incomplete.

One way the WHO investigators got around this was to focus their analysis on the confirmed or probable cases of Ebola. They placed much less emphasis on the more uncertain “suspected cases”. Hence, the data can be viewed as a broadly useful estimate of the situation. It is not precise but, given the circumstances, it is unlikely that significantly better information will be available any time soon.

The team found that the infectiousness and fatality rate of this Ebola outbreak was similar to previous smaller outbreaks. They thought this outbreak was much larger and more serious because the populations affected were different – for example, the populations of Guinea, Liberia and Sierra Leone are highly interconnected. The report said there was “much cross-border traffic at the [Ebola outbreak] epicentre and relatively easy connections by road between rural towns and villages, and between densely populated national capitals. The large intermixing population has facilitated the spread of infection”.

However, they said the large epidemic in these countries was not inevitable. They explained how in Nigeria, including in densely populated large cities such as Lagos, the disease was contained, possibly due to the speed of implementing rigorous control measures.

There was, however, a glimmer of hope in the otherwise worrying report. It discussed how, based on previous outbreaks, new cases of the disease can be reduced within two to three weeks of introducing disease control measures.

The report called for a swift improvement in current control measures to address this problem, specifically:

  • improvements in contact tracing
  • adequate case isolation
  • increased capacity for clinical management
  • safe burials
  • greater community engagement
  • support from international partners

Want to help, but don’t know how? A donation to one of the medical charities that are helping to combat the spread of Ebola could help. A quick online search for "Ebola charities" will bring up a range of deserving causes for you to choose from.

Analysis by Bazian. Edited by NHS ChoicesFollow Behind the Headlines on TwitterJoin the Healthy Evidence forum.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Ebola death rates 70% - WHO study. BBC News, September 23 2014

Ebola outbreak: Experts warn cases could number one million by January as 'window closes' to stop disease becoming endemic. The Independent, September 23 2014

Experts warn Ebola could infect 1.4 million by January in just two African nations. Mail Online, September 23 2014

Links to the science

WHO Ebola Response Team. Ebola Virus Disease in West Africa — The First 9 Months of the Epidemic and Forward Projections. The New England Journal of Medicine. Published online September 23 2014

Meltzer MI, Atkins CY, Knust B, et al. Estimating the Future Number of Cases in the Ebola Epidemic — Liberia and Sierra Leone, 2014–2015. Morbidity and Mortality Weekly Report. Published online September 23 2014


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