How will we know when the number of Ebola infections starts to decline?

According to the World Health Organization (WHO), three West African countries continue to experience intense transmission of Ebola. More than 16,000 cases of Ebola have been reported from Guinea, Liberia, and Sierra Leone in the past several months since the outbreak started earlier this year (link). There is some evidence that the rate of new Ebola infections in these countries is not growing as fast as previously estimated which is good news. The WHO situation report published on November 26, 2014 (link) states “Case incidence is stable in Guinea, stable or declining in Liberia, but may still be increasing in Sierra Leone”.

However, there is great uncertainty over the quality of the reporting data emanating from West Africa on this Ebola outbreak. Also, based on the fluctuating numbers of newly reported cases in each of these three countries, it is difficult to assess the increases or decreases in the incidence of cases in these three countries. Assuming that the case numbers reported in the WHO situation reports are representative the number of infections in each of these countries, the average number of new cases per day can be graphed on a timeline. Below, the average number of new cases per day is compared with the cumulative moving average of cases since the start of the outbreak within each of the three countries.

These graphs clearly show that the trajectory of the number of new cases in each country generally support the WHO statement. At this time, the number of new  daily cases  in Guinea appears to be declining towards the cumulative moving average. Recent new case counts for Liberia have fallen below the long term cumulative moving average. For Sierra Leone, the reported average number of Ebola cases is above the cumulative moving average,  This is a clear indication that rate of Ebola infections in Sierra Leone have not yet started to decline.

Eventually, declines in the number of new Ebola infections in these three countries will only be apparent when the daily average of newly reported Ebola cases drops below-and stays below-the cumulative moving average. At that time the cumulative moving average will begin to decline as well. Comparing the number of daily new cases in these countries in relation to the cumulative moving daily average will help identify when there is a downturn in the number of new Ebola infections in these countries. 

Graph Notes:

1. Data used to construct these graphs is derived from the country totals provided by WHO in the Ebola situation and data updates current through November 28, 2014 (link). The new daily cases counts includes all Ebola cases reported from the country including, confirmed, probable, and suspected cases.

2. The average number of new Ebola cases per days is computed as the total number of newly reported cases since the last report divided by the number of reporting days. The average number of new cases per day is recalculated after each WHO report.

Comparing WHO and CDC Projections of Ebola Cases in the Future

Through October  12, 2014, the World Health Organization  (WHO) has reported more than  8900 cases of Ebola since this epidemic began  (link).  The outbreak is currently out of control in three countries in West Africa, Guinea, Liberia, and Sierra Leone.  The graph below depicts the timeline of the growth of the  cumulative number of total cases reported by  each of these countries.  

 

The overall cumulative Ebola case total time series can be fitted to an exponential growth curve to project the total number of cases going into the future. The WHO data indicate that by January  2015 there will be almost 45,000 Ebola cases as shown in the graph below.

 

There is no doubt now that this outbreak will not be contained in West Africa by the end of December.  How many future cases of Ebola will there be is difficult to predict. WHO has noted on several occasions that the officially reported numbers under represent the actual number of cases and deaths in these countries.

On the other hand,  The US Center for Disease Control  (CDC) has projected cases counts ranging from 550,000 to 1.4 million cases in Sierra Leone and Liberia by mid January 2015 (link).  The CDC adjusted  existing case counts by a factor of 2.5 according to their model (as of August 28, 2014).  The graph below compares the differential growth rates based on current WHO data and the estimated case count by the CDC.  According to the CDC estimates, there are now at least 22,000 Ebola cases in West Africa compared to the 8900 reported by WHO.

The graph indicates the clear disparity in the different estimates by these two health agencies of the future case count of Ebola.  As we edge closer to the end of 2014 we will have a better idea of which projection is more accurate.

Where does the WHO estimate of 5,000 to 10,000 new Ebola cases in December come from?

The number of Ebola infections in West Africa continues to increase at an alarming rate (link).

As the official international public health agency, the World Health Organization (WHO) is tasked with tracking and reporting on infectious diseases around  the world.  As of October  14, 2014 the WHO has reported more than 8900 Ebola cases from the three West Africa nations of Guinea, Liberia, and Sierra Leone, where the Ebola outbreak has not yet been contained (link).

Below is a chart showing the continued rising number of new cases by week number in these three countries.  The data in the chart is based on official WHO data through October 12, 2014 (link).  A quote from Dr. Bruce Aylward,  a WHO spokesperson,  indicates that by mid December 2014 between 5,000 to 10,000 new weekly Ebola cases could reported in the three West African countries  (link).

The next graph below shows the temporal progression of the increases in new cases with a trend line projecting news cases into the coming weeks. The exponential trend line from the current  WHO data projects 5,000 to 10,000 new weekly cases of Ebola in West Africa by December 2014. This is the basis of Aylward's comments yesterday.

Crowd sourcing for a solution to the West African Ebola epidemic

 With the current Ebola outbreak raging in West Africa and with no immediate solution in sight,  the U.S. Agency for International Development (USAID) has proposed an online challenge to think "outside the box" regarding solutions for the current Ebola crisis.

Today, USAID launched the Fighting Ebola: A Grand Challenge for Development with a call to innovators around the world to submit ideas focused on improving the tools used by frontline healthcare workers in the fight against Ebola in West Africa. The initial focus of the Challenge, as announced by President Obama on Sept. 26, is to generate pioneering solutions to improve the personal protective equipment (PPE) and tools used by healthcare workers battling Ebola.

The Fighting Ebola Grand Challenge will help to identify innovations that improve the comfort while maintaining the safety of PPE – masks, gloves, boots, and other protective gear used by healthcare workers.

The website is an open innovation platform to crowd source and incubate innovative ideas to improve delivery of care and stem the spread of disease, including improvements in PPE;  a  challenge competition to fund and test innovations for PPE, infection treatment and control; and  partnerships for rapid testing and deployment of the best solutions.

To share your ideas or to join the conversation, visit http://ebolagrandchallenge.net.

Map: Countries with Confirmed Ebola Cases from the 2014 Outbreak

As of October 6, 2014, seven countries have reported cases of Ebola as noted below.  The Democratic Republic of Congo has reported at least 53 cases from a local Ebola outbreak (link)  not associated with the current outbreak that apparently originated in Guinea in December 2013 (link).  

Guinea (977 confirmed cases) link

Liberia (931 confirmed cases) link

Nigeria (19 confirmed cases) link

Senegal (1 imported infection) link

Sierra Leone (2179 confirmed cases) link

Spain (1 locally acquired infection) link

United State of America (1 imported infection) link

Spain: The First Locally Acquired Ebola Infection in Europe

A health care worker in Spain is the first individual outside of Africa to locally acquire an Ebola infection.  A nurse treating an Ebola case in a Madrid hospital in September has tested positive for Ebola (link). The nature of transmission from the Ebola patient to the nurse has not yet been reported.  The reports from the Ebola outbreak in Africa show that health care workers are frequently infected and die from treating Ebola patients (link). It was widely assumed that health care workers in the West Africa countries became infected because of lack of adequate PPE, proper training, and overwhelmed facilities. This new case in a European hospital raises concerns about the nature of Ebola transmission in hospital settings everywhere in the world.   

The Ebola case in Texas, USA, will provide an additional test of the nature of transmission of this virus (link). So far no secondary cases have been reported in Texas. It will be several more weeks before Texas can claim no additional secondary cases of Ebola.