Ebola - Some Hope for Control in West Africa

Ebola, as we all know, is out of control. As an example, every time I turn on the TV there is Dan or Mike or Dan staring back at me. Eventually, we will calm down in the US and begin to focus our attention on the critical outbreak in West Africa. My prediction is that this will happen sometime soon after November 4th (Election Tuesday). In the meantime, there is some possibly, maybe, hopefully good news out of West Africa in today's NYT. As of a few days ago, fewer than half of the 649 available treatment beds in Liberia were occupied. Of course this could be good or bad, but I'm holding out for good.

There was also some potentially good news in a report published in the Annals yesterday. Dan Yamin et al. analyzed a stochastic model of Ebola transmission populated with parameters from a 2000-2001 Uganda outbreak and the current outbreak in Montserrado County Liberia. The authors used the model to determine the number of secondary cases infected by survivors or non-survivors and also evaluated the effect of isolating/hospitalizing patients. I have included the key figures from the paper below. In Figure 1a, they estimate the Ro stratified by whether the index case was a survivor or non-survivor. For the whole cohort, the Ro was 1.73. However, the difference between non-survivors and survivors is striking. It appears that non-survivors infect four times as many people as survivors (2.36 vs 0.66). This may explain why the two Dallas nurses were infected after being exposed to a non-survivor while no secondary cases have yet occurred in other US hospitals, where everyone else (so far) survived.

Figure 1a
In Figure 1c, the authors provide an estimate of the average number of secondary cases per day of symptomatic disease. You can see that there is very little transmission in the community at day 1 and it remains very low for survivors but jumps up after day 2 for non-survivors. This implies that waiting for symptom development is a scientifically valid strategy for preventing community transmission of Ebola even in Africa. (We expect these numbers to be far lower in the US where our communities are less crowded and we are fortunate to have toilets, indoor plumbing and clean water.)

Figure 1c

Finally, in Figure 2 the authors evaluated at what time point non-survivors (very sick individuals) must be actively isolated to prevent community transmission. They estimate that if 75% of the non-surviving cases are detected and isolated by day 4 this results in a 74% chance of disease elimination and if 100% are detected and isolated by day 4 then there is a 94% chance of disease elimination. Currently, the authors report that the average time from disease onset to hospitalization in Liberia is 5 days, so there is some room for improvement. However, I suspect that the current expanded efforts could achieve 4 days. When I put the results of this Annals paper together with the NY Times report of empty beds, it suggests that there is available capacity to hospitalize and isolate patients within 4 days of symptom onset and it might even suggest that current efforts are already working. I'm certainly hoping this is the case.

Oh, and if isolating patients 4 days after symptom onset works in West Africa, it means WE DON'T NEED TO QUARANTINE ASYMPTOMATIC FOLKS IN THE US. So please stop it...and sorry for shouting.


  1. Thank you for this very informative post! This seems to confirm that it is mostly safe to avoid isolating or quarantining people until they have symptoms.

    And yet, most people I talk to at work (I am a biomedical scientist) seem to feel that it would be much better to stop resisting the idea of a mandatory quarantine. They argue that it would be safer and cheaper to quarantine everyone coming from affected countries or working with Ebola patients and pay them for lost wages and disruption to travel plans, than to deal with the fallout like it happened in Ohio.

    I am very curious why there is such a disconnect between public health experts and the general public when it comes to evaluating potential harms and benefits of a quarantine.

  2. Thanks for your comment. I think no HCW will go to Africa under such conditions, so we are just extending the outbreak which will kill more in Africa (and some in US). Bogus policy to placate unfounded community fear has consequences and HCW are under no obligation to go to W Africa when they are treated like lepers.

    Another extension of this "mandatory quarantine" is isolation of HCW who care for Ebola patients in the US. I assume those would then be isolated to. Since it took 40 HCW to care for a single patient at Emory, you can see that unnecessary quarantines won't really work if you want us to care for Ebola patients in the US.

    These same unfounded quarantines were imposed during the early HIV outbreak and Boston wouldn't let the first International AIDS conference happen there. With time, scientists pushed back, the public felt comfortable and we all got back to life without bogus quarantine. The same will happen in the US. And scientists will never accept bogus quarantines.

  3. Thank you, that is exactly what I have been arguing (that one would, for example, have to create an isolated community for everyone working with the Ebola patients at Emory, for as long as there is a trickle of infected health care workers returning from Africa for treatment). Under these conditions, it seems that only military personnel would be available to treat patients - here or overseas. And yet that argument does not seem to work even with my fellow scientists...

  4. But doing this isolation community is unnecessary. Every HCW would know that if they felt sick and had fever to get seen. Since infectiousness is so late in Ebola, there is no need for quarantine or any isolated community. Ebola is so different from other pathogens that people are having a difficult time realizing that this is less infectious than any other pathogen - per this Annals article Ro is 0,66 or lower in the US


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