Sunday, March 1, 2015

Ebola's Sword of Damocles

The mainstream American media loves a simple story, and with the West African Ebola outbreak--which is definitely not a simple story--the simple story goes like this:

Almost over!

Insert smiley face. This stands in marked contrast to the narrative from July through October, when everyone thought that Guinea, Sierra Leone, and especially Liberia might come apart at the seams. Now, however, there are confident pronouncements of Ebola's end. Ebola Treatment Units in Liberia sit almost completely vacant, and the number of cases even in Sierra Leone and Guinea is still dramatically lower than from the height of the epidemic, as can be seen here.

My quibble with such a feel-good pronouncement as I sit here in my final day in Monrovia before heading back to the States, leaving behind an unquestionably happier and healthier Liberia than the place I inhabited last October, comes from one fairly obtuse sentence in this week's WHO Situation Report. It almost sounds innocuous, a tumble of epidemiological words in the overview, a seemingly humdrum observation amidst the quiet huzzahs of fewer and fewer deaths.

This is from the first paragraph of the report, and I've emphasized the key phrases: "A total of 99 new confirmed cases of Ebola virus disease (EVD) were reported in the week to 22 February. Guinea reported 35 new confirmed cases. Cases continue to arise from unknown chains of transmission. Transmission remains widespread in Sierra Leone, with 63 new confirmed cases. A spike of 20 new confirmed cases in Bombali is linked to the previously reported cluster of cases in the Aberdeen fishing community of the capital, Freetown. There were 14 new confirmed cases in Freetown over the same period, with cases still arising from unknown chains of transmission in Freetown and elsewhere."

What that means is that, despite having an army of epidemiologists on the ground after several billion dollars of international aid has flooded the area to bring the outbreak under control, we still do not know where the virus is hiding in Sierra Leone and Guinea. This is now in marked contrast to Liberia, which not very long ago seemed the country in most dire circumstances; all current cases of Ebola in Liberia, which number only a few, have all had their chains of transmission identified. What that means is that for everyone who has developed infection, we know exactly where they got their infection from. This is not true for Sierra Leone, and it is not true for Guinea.

If you don't know the chains of transmission, then you can't do proper contact tracing. If you can't do proper contact tracing, you can't set up effective monitoring or quarantines. If you try to institute quarantines when you're shooting in the dark, you increase the chances (which are already significant) that all you're going to do is drive people who might be sick further underground, trying to outrun the quarantine and spreading the virus. This is at least partly the reason why we have seen the outbreak persist in Sierra Leone.

It's also worth noting that, while 99 new cases is a huge improvement over where we were at the height of the epidemic, by historical standards of Ebola outbreaks, 99 new cases in a week is a staggering number. The Kikwit outbreak of 1995, which lasted just under nine months and dominated news headlines for a time, had a total number of 315 cases.

I grant that the story has changed. My concern, however, is that the triumphant tone is premature. We still do not know where all of the cases are coming from. At this point, that is the news story, not the dramatic drop in cases. I find the phrase "unknown chains of transmission" almost as alarming as "Ebola outbreak" itself. We're not done just yet.