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Nigeria declared free of Ebola, but do the maths

Posted By Joanne Nova On October 21, 2014 @ 5:51 pm In Global Warming,Medicine | Comments Disabled

I am glad that Nigeria is officially free of Ebola now. The story is reassuring. New outbreaks of Ebola are stoppable. But the numbers are sobering. They show how far gone the situation is in West Africa.

The index patient (as the source of the outbreak is known) arrived in Lagos, a megacity of 21 million people, on July 20th — a recipe for disaster. Over the next six weeks 19 further people were diagnosed with Ebola. The death toll was eight people, many of them health workers. Those infected generated 989 contacts, and it took 18,500 in-person, follow up visits to make sure that the virus did not spread further.

Translate those ratios to West Africa, where the latest WHO situation report shows there were 2,638 new cases between September 26 and October 17. In Nigeria, each infected person on average generated 50 contacts, and each contact generated 18 follow-up visits. This is only the roughest of ballpark estimates, but if the ratios were similar, it means that solving the spread in Liberia, Sierra Leone, and Guinea would generate 130,000 contacts and require 2.4 million follow-ups in the next three weeks. By mid November that will double. Obviously things are too far gone to use the same techniques in West Africa, and the strategy must be to strategically prioritize the actions that reduce the Ro (reproduction rate) to slow that exponential curve.

If airborne transmission occurs, it must be reasonably small. The message from Nigeria is that patients are not that infectious until they hit the late stages and are hospitalized or close to it. Dr Stella Adadevo probably saved Nigeria from disaster, but tragically died from Ebola herself. We must do more to save the heath workers. (Surely we can organize blood transfusions from survivors?)

A new study suggests three people a month will fly from West Africa with the virus if no exit screening takes place. (I’m not sure how useful that number is, given the exponential growth curve, and the non-random selection of high risk people seeking better hospitals.)

Scientific American discusses the way Nigeria controlled the outbreak. It was not rocket-science:

  • Fast and thorough tracing of all potential contacts
  • Ongoing monitoring of all of these contacts
  • Rapid isolation of potentially infectious contacts

One patient in Nigeria generated 526 contacts because they flew to Port Harcourt, but only three got sick. So the estimates of “50 contacts” per patient may be skewed far above the norm. But since the estimates of cases in West Africa are likely underestimates of the real total, the number of follow-ups required is still in the millions. It’s too late now for the ideal track and containment approach.

Grim statistics on beds required

BBC news assembled these figures from the WHO report October 12. Liberia needs 2310 beds now.  We need an extra 5000 beds there in the next month to even catch up to the curve, let alone to get ahead.

 Country  Existing Bed Capacity  Total Beds Needed Extra beds required
Guinea 160 260 100
Liberia 620 2,930 2,310
Sierra Leone 346 1,198 852

The US situation

The CDC has finally issued updated new stringent protocols for Ebola.  This hopefully will stop healthcare workers from being infected.

The second Nurse in Texas flew on October 10 and 13, so we are a full 7 days beyond that, and no other person so far has been diagnosed. The immediate family of Duncan Thomas (the first Ebola death in Texas) have been cleared, with a total 43 people taken off the Ebola monitoring list in Dallas, but 120 are still under watch.  The next week is particularly important.

From the UNMEER latest report October 20th.

A new mobile lab can diagnose Ebola cases in three hours instead of 2 – 5 days. But it does 16 samples at a time in  Liberia, where there are currently over 100 new cases a day.

Food prices have risen by an average of 24 per cent across Guinea, Liberia and Sierra Leone
forcing some families to reduce their intake to one meal a day. The FAO and WFP said that
decisions by these three governments to quarantine districts and restrict movements to contain the
spread of EVD have also impacted markets and reduced food security.

Sources: US Dept of Health  — Information  | Science Mag | Clinical features | Genome Ebola Portal | Timeline | Projection  | CDC on Ebola | Twitter #ebola |

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