Ebola outbreak map: Why has the disease spread so fast in Liberia? And how many people have died in the country so far?

Billy Ehrenberg
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The Ebola crisis has hit one country worse than all the others: Liberia has suffered an estimated 46 per cent of cases and, at 1,200, twice as many deaths as any other country.

Sierra Leone and Guinea, the other two countries where the disease is widely transmitted, are suffering too, but the disease is at its most rampant in Liberia. According to World Health Organisation (WHO) figures there have been 4,262 cases and 2,484 deaths in the country so far.

Why is it worse this time?

Part of the reason is likely to be urbanisation. In past outbreaks, like that in the Democratic Republic of Congo (then Zaire) back in the 1970s, the outbreak was usually isolated to one village.

But populations are rising, as is population density. The national figure is 93 people per square mile (2008 census), a 66 per cent increase on the 1984 figure of 56.

This average is exceeded in the Liberian counties of Montserrado, Margibi, Maryland, Bomi, Nimba and Bong.

Add that to the fact that at first people didn't believe the virus was real, claiming healthcare workers were actually infecting people with the virus, and you can see why Ebola has spread so fast. Tradition has played a role too: bodies remain highly infectious even after death, and the customary washing of deceased persons has spread the disease.

The map below shows population density (shading) in different Liberian counties, and the number of cases (bubbles). The data is from the Liberian government not the WHO.

It stands to reason that the places with the highest populations should suffer most because of the way the disease spreads: through bodily fluids. As it isn't airborne, it is difficult for the virus to cross sparsely populated regions, which could explain the lower rates of prevalence (see next map) in the east of Liberia.

Look at the key and you'll see the breaks in colours aren’t equal interval: there is such a huge jump between the rural areas and the county of Montsserado, which contains the capital Monrovia that the map wouldn't have been illustrative at all. Monteserrado has a population density of over 1,500 person per square mile. It is much higher in the city itself, although the 2008 census doesn’t give a figure.

The buildings aren’t high rise flats so the figure looks deceptively low: London has a density of over 11 thousand.

Where the difference comes is that in Monrovia there were 4.7 people living in every dwelling, whereas the figure in the UK is 2.3 according to the Office of National Statistics.

This mixture means the disease has spread rapidly in the capital.

*Figures are estimates, extrapolating the population growth rate at the 2008 census and extending it over the six years since.

Here the different areas are split by equal intervals because the figures per 100,000 are closer together. The blue bubbles represent the (mappable) urbanisations listed by the Liberian government as being home to 5,000 people or more. The bigger the bubble, the more inhabitants.

The largest roads and rivers are included to give some idea of how the virus could be spread around the country.

However Monrovia looks orange, rather than red. This may well be not because the disease is less prevalent there (proportionately) but because not all the deaths are reported and not all the cases attended to. According to the WHO:

The true number of deaths will likely never be known, as bodies in the notoriously poor, filthy and overcrowded West Point slum, in the capital, Monrovia, have simply been thrown into the two nearby rivers.

It is likely, therefore, that the numbers are actually much higher.

The poor conditions in the capital also mean it has an extremely high mortality rate, with 70 per cent of victims dying (according to our analysis of government figures).

The blue bubbles represent the number of cases and the red bubbles the number of deaths. The larger the red bubble compared to the blue, the higher the fatality rate. The coloured shading visualises the same information.

Government data from a week ago is vague on these rates. The map uses the totals for probable and suspected cases (as well as confirmed) because it is likely that even if not all suspected cases are Ebola, the real number of sufferers is much higher anyway.

As is widely reported, prompt and thorough treatment can dramatically increase the chances of a patient surviving. Here is a graph with the data from the map:

Medical staff in the line of fire

Healthcare workers are at risk, as the contaminations of staff in Texas and Spain have shown. What is more, as the number of healthcare workers being infected per 100 cases varies.

Doctors and nurses are becoming increasingly overwhelmed as the number of cases increases. As far back as 28 August, the WHO said 40 per cent of all cases had occurred in the previous three weeks.

Obviously some counties have higher proportions but the infection rates are not good. In Monteserrado, five healthcare workers get infected for every 100 cases. Across the country the rate is 4.9, and it is as high as 10.5 in Rivergee and Grand Cape Mount. Both have had few cases, perhaps meaning that health workers have not had as much experience.

This method of comparison is limited as we don’t know how many healthcare workers there are in different areas.

This map shows where healthcare workers have caught the disease and where there are most cases.

To make matters worse, CNN has reported that some health workers are considering striking as a result of poor conditions.

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