CDC: Ebola cases in West Africa could exceed 550,000 by January

Date: Sep-24-2014In their latest report on the current Ebola epidemic in West Africa, the US Centers for

Disease Control and Prevention urge that immediate interventions be put in place quickly, and warn

that the "cost of delay will be devastating."

If current trends continue, they say the future number of cases in Liberia and Sierra Leone

could exceed 550,000 by January. That estimate is based on reported cases. If under-reporting is

taken into account, their calculations suggest that figure is likely to be nearer 1.4 million.

While the Centers for Disease Control and Prevention (CDC) say they cannot guarantee the accuracy of their estimates, they are clear about

their key messages: "if conditions remain unchanged, the situation will rapidly become much worse,"

and they serve as "a warning and a call to action."

The CDC report their calculations - and how they arrived at them with a new model - in their latest

Morbidity and Mortality Weekly Report (MMWR). The report details the CDC estimates for

future Ebola cases in Liberia and Sierra Leone, where the epidemic is uncontained and out of

control.

Number of cases doubling every few weeks

The report notes that on March 22, 2014, there were 49 reported cases of Ebola virus disease

(usually referred to as Ebola) in Guinea, where the current outbreak in West Africa began.

According to the CDC, there will be up to 21,000 cases of Ebola in Liberia and Sierra Leone by the end of September.

By

the end of August, the outbreak had spread to neighbouring Liberia and Sierra Leone, and the total

number of probable, confirmed and suspected cases had risen to 3,685.

The CDC estimate that by the end of September, there will be around 8,000 Ebola cases - or as

many as 21,000 cases if corrections for under-reporting are included - in Liberia and Sierra

Leone.

And if current trends continue, "without additional interventions or changes in community

behavior," these figures will rise to around 550,000 cases - or 1.4 million including under-reported cases.

The estimates assume the current conditions of disease transmission will remain unchanged. The

main driver of the estimates is that in Liberia, the number of cases is doubling about every 15-20

days, and in Sierra Leone and Guinea, they are doubling around every 30-40 days.

EbolaResponse modeling tool takes into account disease stages and types of isolation

For their calculations, the CDC constructed a new modelling tool called EbolaResponse, comprising an Excel

spreadsheet containing a set of formulae and assumptions.

The model allows researchers to estimate the daily movement of patients within disease stages

(i.e. susceptible, incubation, infectious, recovery or death) using probabilities for three

different types of isolation.

The three different types of isolation are: hospitalization (such as in an Ebola treatment unit

or medical care facility), home with effective isolation (a home or community setting where there

is reduced risk of disease spread, including safe burial where needed), and home with no effective

isolation.

Ideally, Ebola treatment units and appropriate medical care facilities have infection control

procedures that prevent disease spread, but the CDC note this is not always the case. So the model

assumes there is an average daily risk that transmission will occur - however this is fewer than

one person infected per infectious patient.

The model includes information from previous Ebola outbreaks - for example, periods of

infectivity, time between exposure and illness. There is no evidence that the virus is spreading

differently from previous outbreaks.

To estimate the number of under-reported cases, the report uses a factor of 2.5. This was

calculated using estimates of beds-in-use from the model and comparing them to expert opinions of

actual beds-in-use on a given day (August 28th). The difference is a potential under-reporting

correction factor (1.5 more beds were being used than the model estimated.)

'Cost of delay will be devastating'

The CDC say we know how to control and stop the epidemic. The model suggests this will require

about 70% of people infected with Ebola be cared for in Ebola treatment units, or if these are

full, they should be cared for at home or in a community setting, where risk of disease is reduced

and burials are conducted safely.

Every month of delay in reaching this 70% target will increase the number of cases and deaths,

and the need for more beds and resources. "The cost of delay will be devastating," say the CDC.

If we are to avoid the catastrophic scenario the model projects for January, effective

interventions need to occur quickly, says the federal agency. This includes "appropriate disease

control methods, communication, changes in community behavior, and adequate resources (such as

staff, beds, equipment, supplies)."

The CDC model estimates the number of beds that would be needed in medical facilities and Ebola

treatment units, but it is not designed to give details of resources such as enhanced protection

measures to minimize disease spread.

In a recent Science editorial, Peter Piot, who in 1976 co-discovered the Ebola virus in Zaire

(now Democratic Republic of Congo) while working at the Institute of Tropical Medicine in Antwerp, Belgium, says that the current Ebola crisis requires a "rapid response at a

massive global scale."

Now a professor at the London School of Hygiene & Tropical Medicine, Prof. Piot says the

epidemic in West Africa is the result of a "perfect storm" that combines dysfunctional health

services, low trust in Western medicine and governments, denials that the Ebola virus exists, and

unhygienic burial practices.

Meanwhile, the UN Security Council has resolved that the Ebola outbreak in Africa constitutes a

threat to international peace and security, and calls on member states to respond urgently to the

crisis.

The crisis is so urgent that an expert panel of the World Health Organization (WHO) concluded in

August that it would be ethical to evaluate unregistered investigational treatments for Ebola virus

disease in people.

To this end, the aid agency MSF/Doctors without Borders, recently reported that

Ebola treatment trials are to be fast-tracked in West Africa for the first time.

Written by Catharine Paddock PhD

View all articles written by Catharine, or follow her on:

Courtesy: Medical News Today Note: Any medical information available in this news section is not intended as a substitute for informed medical advice and you should not take any action before consulting with a health care professional.