Yesterday’s MMWR worst case estimate of between 550,000 and 1.4 million Ebola cases in Liberia and Sierra Leone by the end of January - if interventions are not implemented - (see MMWR: Estimating The Future Number of Cases In The Ebola Epidemic) has garnered predictable headlines while the CDC’s caveats regarding the interpretation of these numbers generally appears much further down the page.
CDC Director Dr. Thomas Frieden has been quick to point out that this report is based on `month-old data’ and that it doesn’t take into account recent and future interventions, but the `hook’ for most overnight reportage reads along the lines of:
The World Health Organization meanwhile has provided a far more subdued short-term projection that if interventions aren’t initiated the number of cases could climb to 20,000 by early November (see NEJM Ebola Virus Disease in West Africa — the First 9 Months and Forward Projections).
Both the CDC and WHO have expressed optimism that the `worst-case scenario’ can be avoided by the surge of international assistance now headed to the region.
That said, rarely do major disaster response operations go as well as hoped, and the challenges presented by this crisis are unprecedented. How much optimism is warranted is something we won’t know for several months.
The CDC has released some ancillary documents for this MMWR report, including a statement from CDC Director Frieden and a Fact Sheet on the findings. Since these sorts of provisos often get short shrift in the media, I’ve provided links and excerpts below:
For Immediate Release: Tuesday, September 23, 2014
Contact: Media Relations
Ebola is a critical issue for the world community. This week’s meetings in NY and Washington are a critical opportunity for increased international commitments and, more importantly, action.
The Ebola case estimates published today in the MMWR are based on data from August and reflect a moment in time before recent significant increases in efforts to improve treatment and isolation. They do not account for actions taken or planned since August by the United States and the international community. We anticipate that these actions will slow the spread of the epidemic.
The Ebola Response model is an important tool for people working to stop Ebola. It provides the ability to help Ebola response planners make more informed decisions on the emergency response to help bring the outbreak under control – and what can happen if these resources are not brought to bear quickly.
The model shows that there are severe costs of delay, and the need for increased resources and immediate and ongoing action by the international community.
It is still possible to reverse the epidemic, and we believe this can be done if a sufficient number of all patients are effectively isolated, either in Ebola Treatment Units or in other settings, such as community-based or home care.
Once a sufficient number of Ebola patients are isolated, cases will decline very rapidly – almost as rapidly as they rose.
Tom Frieden, M.D., M.P.H.
Director, Centers for Disease Control and Prevention
Excerpts from the Fact sheet:
Ebola Response Modeling Tool
CDC has developed a dynamic modeling tool called Ebola Response that allows for estimations of projected cases over time in Liberia and Sierra Leone. The Ebola Response modeling tool was used to construct scenarios to illustrate how control and prevention interventions can slow and eventually stop the Ebola epidemic. Importantly, it can help planners make more informed decisions about emergency response resources to help bring the outbreak under control. It allows input of data reflective of the current situation on the ground in affected countries and communities. The Ebola Response modeling tool is intended to help local governments and international responders generate short-term estimates of the Ebola situations in countries, districts, and villages. The tool, in the form of a Microsoft Excel spreadsheet, will be freely available online.
Projecting Ebola Case Estimates
Published today in MMWR, CDC used the Ebola Response modeling tool to calculate Ebola cases through mid- January in Sierra Leone and Liberia, providing an example of how this tool can be used. The MMWR estimates a range of between 550,000 and 1.4 million cases by January 20, 2015. The top range of the case estimate, 1.4 million, is explained by the model’s assumption that cases are significantly underreported by a factor of 2.5. It is essential to note that these numbers reflect a moment in time based on scientific and epidemiological data available in August, which did not account for the ongoing U.S. government Ebola relief effort. The numbers do not reflect current conditions. Modeling suggests that extensive, immediate actions – such as those already started – can bring the epidemic to a tipping point to start a rapid decline in cases.
The most important part of the report describes the potential effect of public health actions. The news is encouraging. If we do nothing, things could become much worse. If we take the actions that are planned, things will still be very hard, but we can stop Ebola. The United States and its partners are taking action every day.
Using the Ebola Response modeling tool, we see that the epidemic can begin to be controlled when individuals with Ebola are effectively isolated in Ebola treatment units (ETUs) or in isolation settings in which there is a reduced risk of Ebola transmission. The model also shows a benefit when safe burial practices are implemented that eliminate exposure of healthy individuals to the bodily fluids of the deceased, which often occurs with the use of traditional burial practices. The model indicates that once a tipping point is reached, cases will decline about as rapidly as they had increased. Of note, gains below such a tipping point can also significantly reduce cases.