Saturday, 22 August 2015

Watch that last step, it's a doozy..

For each of the past five weeks, Guinea has continued to throw up 1-5 Ebola virus disease (EVD) cases. But transmission chains are known and so this will hopefully stop very soon. Tracking down contacts that have been lost to follow-up and unknown spread in the community remain big variables in this equation. 

Sierra Leone has reported 1-3 EVD cases over that period - but importantly, the last of those cases was reported by the World Health Organization (WHO) on the 10th of August - 12 days ago. We've seen one full case-free reporting week so far, and the next is looking good for Sierra Leone as well. 

The latest confirmed EVD case data plotted below - which stretches from February to last Friday - we can really see how the death of an epidemic has occurred in steps. For Liberia, there was a very dramatic and precipitous decline, but for Sierra Leone and Guinea, it has been a slower process. 

It looks like we will see an end to the EVD epidemic as we saw it begin, with Guinea harbouring cases. 

And then we wait, watch and remain wary as the 21-day individual incubation periods elapse, then the 42-day national incubation periods lapse, indicating no known ongoing transmission, and finally the many months of vigilance pass. I'm not sure we're really that confident about the upper limit of this final step yet. 

I can't imagine the period of vigilance will pass entirely without incident - Liberia has already taught us a hard lesson about occult transmission - but we've all been wrong about Ebola virus before and it would be great to be wrong about this. Here's hoping those final steps are a smooth descent to zero.


Confirmed cases added by each WHO Situation Summary of Situation Report.
Modified from my Ebola virus disease graphs and tallies page.
Click on image to enlarge