The Ebola virus

The Ebola virus

Val Altounian/Science

How does Ebola spread? Hard facts from key studies

About 5 minutes into Tuesday’s press conference describing the first U.S. Ebola diagnosis, Tom Frieden, director of the U.S. Centers for Disease Control and Prevention (CDC), segued from talk of on-the-ground aid in Africa by saying, “But ultimately, we are all connected by the air we breathe.”

That comment—meant to express the importance of controlling the spread of the virus both overseas and in the United States—compelled Edward Goodman, an epidemiologist at Texas Health Presbyterian Hospital Dallas, who spoke after Frieden, to clarify: “Ebola is not transmitted by the air. It is not an airborne infection.”

Many news stories have driven home the point that the virus is mainly transmitted through direct contact with bodily fluids, people are only infectious when they develop symptoms, and it’s unlikely that Ebola will evolve to become airborne.

But there’s precious little data on some other practical questions: Which bodily fluids harbor the virus? Does it linger on objects touched by an infected person?

Hard data are scant in large part because Ebola outbreaks have been sporadic, and because every epidemic before the current one ended before even 500 people became infected. A few epidemiologic studies have interviewed infected people and their close contacts and clarified that it does not spread through the air. The studies also suggest that the main routes of transmission include touching an infected person, sharing a bed, and of course contact with bodily fluids. Funerals of Ebola patients also presented extremely high risks because of rituals that involve touching the body, group hand-washing, and communal meals.

One study examined skin from people who died from Ebola and suggested that sweat may play an important role. “One possible explanation for the role of direct physical contact in transmission is the presence of abundant virus particles and antigens in the skin in and around sweat glands,” the authors concluded. But the most comprehensive analysis done to date notes that risk factors differ depending on the stage of disease, and that people at late-stage disease or death are far more likely to transmit the virus.

A crucial 2007 paper, published in The Journal of Infectious Diseases, offers perhaps the best indication available of where the risks lie, and where they don’t. It analyzed samples from confirmed cases during a 2000 outbreak in Uganda, including people who were acutely ill or recovering. It also looked for the virus on objects, such as desks, walls, and gloves, in an Ebola isolation ward. The study’s numbers are small, but it’s the most detailed analysis published to date.

Below are the 2007 study’s key tables. One major takeaway: Infection is unlikely to come from a fateful encounter with a doorknob, or even from a handshake. The authors point out, however, that the methods they used to detect Ebola haven’t been extensively tested for use on objects, and the virus could have been present at undetectable concentrations.


Where researchers found the virus in an Ebola ward in Uganda

Sample taken from …
Sample color
Virus
culture result
(+/-)
RT-PCR*
result
(+/-)
Outside of ward:      
Changing room wall
Clear
-
-
Changing room desk (outside ward)
Clear
-
-
Exterior surface of door of isolation ward
Clear
-
-
Inside ward, “suspected” side:      
Nurse’s newly placed glove
Clear
-
-
Bed frame
Clear
-
-
Instrument tray for ward rounds
Clear
-
-
Inside ward, “probable” side      
Air (tube opened and capped, negative control 1)
Clear
-
-
Sterile swab (negative control 2)
Clear
-
-
Intravenous fluid support pole
Clear
-
-
Light switch
Clear
-
-
Floor
Clear
-
-
Handle of 0.05% bleach solution dispenser
Clear
-
-
Nurse’s clean apron
Clear
-
-
Nurse’s clean glove
Clear
-
-
Cle stethoscope
Clear
-
-
Stethoscope after use
Clear
-
-
Stethoscope after use and rinsing with 0.05% bleach solution
Clear
-
-
Bed frame
Clear
-
-
Bedside chair (2 different samples)
Clear
-
-
Food bowl
Clear
-
-
Spit bowl
Clear
-
-
Skin (hand) of patient attendants (3 different samples)
Clear
-
-
Clean glove of patient attendant
Clear
-
-
Corpse decontaminated with 0.5% bleach solution
Clear
-
-
Body bag decontaminated with 0.5% bleach solution (2 different samples)
Clear
-
-
Clean mattress
Clear
-
-
Intravenous tubing
Clear
-
-
Doctor’s blood-stained glove (positive control 1)
Pink
-
+
Bloody intravenous insertion site (positive control 2)
Red
-
+
% of all samples
0
7

*The Ebola Files: Given the current Ebola outbreak, unprecedented in terms of number of people killed and rapid geographic spread, Science and Science Translational Medicine have made a collection of research and news articles on the viral disease freely available to researchers and the general public.

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A 3D plot from a model of the Ebola risk faced at different West African regions over time.
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