Ebola Science

There is a limited set of papers in the literature regarding Ebola transmission to guide the policy making people. A recent NEJM paper presents data on the current outbreak and it is of substantial merit. Their discussion of viral load is on point:

We determined the viral load of EBOV at the time of presentation in 65 patients with a known outcome by means of quantitative RT-PCR. A positive correlation was noted between the viral load and the risk of death. Patients who presented with fewer than 100,000 EBOV copies per milliliter of serum had a case fatality rate of 33%, whereas those with a viral load of 10 million EBOV copies per milliliter or more had a significantly higher case fatality rate of 94% (P=0.003) Viral loads were quantified for a limited number of patients at multiple times during their hospitalization, with results suggesting that an inability to clear the virus was a risk factor for death, even though some patients with prolonged viremia survived

 What seems still to be missing is a detailed progression analysis. Namely what is the minimal load for infection and where on the body and how quickly do the virions reproduce.

In an earlier article in the Journal of Infections Diseases they have performed an analysis of actual contagion. They state:

We conclude that EBOV is shed in a wide variety of bodily fluids during the acute period of illness but that the risk of transmission from fomites in an isolation ward and from convalescent patients is low when currently recommended infection control guidelines for the viral hemorrhagic fevers are followed.

They conclude:

Taken together, our results support the conventional assumptions and field observations that most EBOV transmission comes from direct contact with blood or bodily fluids of an infected patient during the acute phase of illness. The risk of casual contacts with the skin, such as shaking hands, is likely to be low. Environmental contamination and fomites do not appear to pose a significant risk when currently recommended infection control guidelines for the viral hemorrhagic fevers are followed. Prospective studies with the collection of a greater number of clinical samples from patients at different stages of EHF, as well as environmental samples analyzed with an assay validated for EBOV detection in such samples, should be performed to confirm our results.

The actual mechanism and the growth mechanics is still unknown. Thus the science is reflective on cases but not prescriptive on putative cases. It is still problematic as to the risk of those "exposed" since the definition of being exposed is still a work in progress.

Thus the problem for policy people is that the "science" is still in a development stage and does one err on the side of caution or assume that transmission is highly unlikely. Also the time from exposure to time of symptoms seems to be about 12 days, and the proposed quarantines are 21. This may or may not make sense.

The "bottom line" is that despite what some say, the "science" is still in a state of flux and reliance on anecdotal evidence is useful but not definitive.