Les Roberts – “Day 53: What R0 is not.”

Les Roberts – Freetown, Sierra Leone – November 26th, 2014

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Day 53: What R₀ is not

If you believe all those old CDC guys, the first cohort of HIV cases in San Francisco in the 1980’s supposedly had sexual encounters with, on average, over 1000 people in the year before becoming ill. Certainly something close to HIV had been circulating around in the Congo basin for decades, if not centuries. CDC has a blood sample in their freezer from an adult male from Kinshasa taken in the 1950’s that contains HIV. Genetic evolutionists put the origin far far before that. And that should not be surprising. Imagine some hunter butchers a chimp and cuts his hand, he gets something close to HIV… maybe it makes him sick, maybe his wife dies too, who would ever know that one or two people died of some slow funky illness in that Congolese village? It was not until HIV got into a hyper-sexually active cohort that enough “infectious momentum” could be in place to get the disease into blood supplies, commercial sex workers, and all those footholds that HIV gained on the road to becoming a major global burden. I am quite sure: what San Francisco bath houses were to HIV, West African funerals have been to Ebola.

There are widespread traditions in Sierra Leone that suggest the body of your loved one needs to be washed to cleanse the spirit so they will be accepted by the ancestors. Allowing them to be buried unwashed would be for many something akin to Christians damning someone to hell. Funeral attendees often kiss the corpse as well… like in the US. Thus, people, usually women, commonly cleanse and wash the body after death. They will then often pour the rinse water over themselves to bask in, and respect, the decedent’s spirit. And, as if that wasn’t microbiologically disastrous enough, then these women usually prepare food for the large number of people coming to the funeral. This is a virus whose concentration in the body spikes with the acute phase of illness and where death often releases millions of viruses that ooze out afterwards. It would be hard to dream up a more perfect way to spread this virus around than the traditional West African wash & rinse funeral. For the first months of this outbreak, almost all big transmission chains were associated with funerals and in the CDC’s VHF dataset, the majority of cases through September reported recently attending a funeral. That fraction has dropped dramatically! Maybe less than 10% now. It may be that the outbreak has enough “momentum” to keep running wild without funeral transmission, but no one knows.

When I got here two months ago, of the major elements needed to achieve the two major UN goals (70% of bodies buried safely and 70% of cases isolating themselves early in the course of illness by seeking treatment), almost nothing was functioning well. Now, major progress has been made on the safe burial front. There are lots of articles written about the burial system falling apart (e.g. http://www.bbc.com/news/world-africa-30191938 ) but those are the exception. The safe burial effort is perhaps the major success. The bad centralized data suggest about half of all deaths are buried by safe burial teams (which is on paper required by law for all deaths) but I suspect the fraction of Ebola deaths buried safely is significantly higher. In our surveillance sensitivity exercises, out in the smallest villages far from the paved roads, most chiefs are adamant about calling burial teams if they think they have an Ebola death. Does the family wash the body before the teams come? Yes, probably. But, it may not be such a huge deal if there are no funerals, no meals, and no kissing the corpse components to the burial. It is stunning how in our field work often eight, ten, or all of a household can get infected with no neighbors getting the disease. Funerals somehow seem to be an incredibly powerful mechanism to move this reluctant but pernicious disease between houses and villages.

Recently, in the most out of the way village I have visited, there were four families out in the fields in the mile before the village and we saw those people as we approached but they always hid as we got close. I am not sure if they fled from Ebola laden villages or were driven out because a family member got sick. Then when our car rolled into this village of around 200 people, everyone slipped inside and there was suddenly no one to be seen. It was only because the driver was from that Chiefdom and spoke with the perfect dialect that people could be lured out. They were scared… scared of anyone from outside and the risk they might bring Ebola. Things are not as they were in July!

By and large, people don’t go to funerals now. Certain people don’t tolerate commercial sex with outsiders. There is a lot changing and I am convinced that in the few weeks to come the outbreak will peak… not because of what the health community has done, but because people have changed their behaviors and thus changed that interaction between virus and culture that determines the R₀. With flu, R₀ is largely determined by the intrinsic nature of the virus and people talk about it, and model it, as if it is an internal characteristic. With suicide, no one would consider the degree to which is contaminable or transmissible some fixed internal characteristic, because, to the extent suicides come in clusters, it is viewed as a social and psychological contagion. In this regard (the degree to which the R₀ is intrinsically or socially determined) , I am convinced that Ebola is far closer to suicide than flu. I am frustrated by our (my!) inability to get NGO’s to step-up and operate treatment centers and the ability to make treatment beds available. (But, our former Emergency Medicine Fellow, Trina Helderman has just come this week bringing the NGO Medair…sort of a Swiss based mini-MSF, so hope lingers.) But, I expect history to show that the outbreak turned around because the people of Sierra Leone changed the communicability of the disease. When that happens, I hope the American public will be able to be convinced that Ebola would almost certainly have an R<1 in the US and spend their fear and energy on more dangerous socially induced diseases, like fat intake, or lack of exercise, or Governors who want to be President.

Onward!

Les