Does new research say Ebola is airborne?

Critics put a months-old fact-check about Ebola back under the microscope last week after they said an article in a scholarly medical journal supported a claim made by George Will that Ebola had gone airborne.

In an October 2014 appearance on Fox News, Will claimed Ebola could be spread into the general population through a sneeze or a cough, saying the conventional wisdom that Ebola spreads only through direct contact with bodily fluids was wrong.

"The problem is the original assumption, said with great certitude if not certainty, was that you need to have direct contact, meaning with bodily fluids from someone, because it’s not airborne," Will said. "There are doctors who are saying that in a sneeze or some cough, some of the airborne particles can be infectious."

PunditFact rated that claim False, and it became one of 16 examples of exaggerations about Ebola that were jointly named PolitiFact’s 2014 Lie of the Year.

On Thursday, however, the Washington Post published a story entitled, "Limited airborne transmission of Ebola is ‘very likely,’ new analysis says." That story began:

A team of prominent researchers suggested Thursday that limited airborne transmission of the Ebola virus is "very likely," a hypothesis that could reignite the debate that started last fall after one of the scientists offered the same opinion.

The conservative blog Hot Air wrote the following day, "PolitiFact’s Lie of the Year of 2014 falls apart only two months later." A blogger named John Patrick Frey said PolitiFact’s Lie of the Year is "the literal truth."

While Will’s claim was not the the Lie of the Year (a group of 16 claims were), we did want to see if new research or science had made Will correct, and us wrong.

So we took that assertion to Michael Osterholm, the lead author of the report quoted by the Post and used as evidence by Hot Air and Frey (who blogs under the identity Patterico). Osterholm is director of the University of Minnesota’s Center for Infectious Disease Research and Policy.

Osterholm says Will was incorrect in his characterization.

"George Will gave people the concept that this could be spread like measles," Osterholm said. "It’s not like that."

So what is it like? Osterholm and other prominent Ebola researchers walked us through it.

What Osterholm’s new paper says

More than 20 researchers and clinicians put their names to the article called "Transmission of Ebola Viruses: What We Know and What We Do Not Know." Osterholm told PolitiFact that it contained nothing that was unknown a few months ago; and it included no new research.

One of the main reasons to write it, Osterholm said, was to bring all the research together in one place.

The hypothesis that the paper included and got the attention of media, said this:

"It is very likely that at least some degree of Ebola virus transmission currently occurs via infectious aerosols generated from the gastrointestinal tract, the respiratory tract, or medical procedures, although this has been difficult to definitively demonstrate or rule out, since those exposed to infectious aerosols also are most likely to be in close proximity to and in direct contact with an infected case. To date, investigators have not identified respiratory spread (either via large droplets or small-particle aerosols) of Ebola viruses among humans. This could be because such transmission does not occur or because such transmission has not been recognized, since the number of studies that have carefully examined transmission patterns is small."

Osterholm helped put that in plain speak for us. He and others believe it is likely that Ebola can spread through aerosols, in the air, but they have no definitive proof that it does, nor do they believe it’s a risk anywhere near the level Will let on. This is an issue, potentially, for doctors and nurses who treat infected patients and have a very special risk of inhaling an active virus.

"All the epidemiology would say it is in close proximity," Osterholm said. "If it occurs at all, it is rare."

Defining aerosol, droplet and airborne particles

It’s about here that we need to throw even more science at you -- specifically when it comes to the words aerosol, droplets, and airborne particles. This is important because size matters, and so does distance.

Aerosol transmission is the umbrella term for a virus spreading through the air. The word aerosol can refer to big particles, droplets, or small ones, called airborne particles.

The big ones, droplets, might come when an Ebola patient chokes when a breathing tube is put down his throat, or during violent vomiting. Droplets can be as small as 5 micrometers or as large as 100 micrometers (100 micrometers is roughly the thickness of a human hair). With droplets, the bigger they come, the quicker they fall. On the large end, the rule of thumb is they travel about 3 feet, scientists say.

The notion that Ebola might spread through droplets is nothing new, and was part of our original reporting.

The small ones, the airborne particles, are less than 5 micrometers and they linger in the air.

So would particles that size carry Ebola, and would the virus be contagious for any length of time? Osterholm and researchers don’t have an answer. In fact, they write that a simple cough can emit particles of many sizes from tiny airborne ones to larger droplets.

The authors write that "the role of aerosol transmission remains unclear. Transmission potentially occurs via virus-laden aerosols generated through forceful emission of body fluids during vomiting, diarrhea, or coughing."

The key there is that aerosol could mean either droplets or the airborne particles. Nowhere does the article say that airborne transmission via small particles has happened or is likely to happen.

The article noted that viral RNA had been found on the outside of surgical masks that were not obviously soiled by a patient’s bodily fluids. Viral RNA is not the same as an infectious agent but if something like the spatter of a patient’s saliva hadn’t hit the mask, it might be that the pathogen got there on by riding on very small airborne particles. In theory, particles that tiny could be inhaled and allow the virus to take hold in the lungs.

But it’s only a hypothesis.

We also spoke to Lisa Brosseau, who is one of Osterholm’s co-authors and also the author of the commentary Will relied on when he made his original claim about coughs and sneezes spreading the disease. Brosseau told us back in October that Will misinterpreted her analysis.

She told us this week that contact with bodily fluids -- not aerosols --  is the pathway for Ebola transmission, and even that danger can be exaggerated.

"I think transmission is unlikely by any route, because even people living in a home with someone who is very sick -- but not taking care of that person -- seem to have a low risk of being infected." Brosseau said.  

Osterholm told PunditFact the prime motivation behind the article was to highlight the gaps in our current understanding of Ebola. Most critically he said, the concern is not with what Ebola is today, but what it might be in the future.

For Osterholm, that future would be bleak if the virus changed and began to spread by people inhaling small airborne particles carrying the virus. "It hasn’t happened yet but what would happen if we had respiratory transmission," Osterholm said. "We need to be mindful of this. We have to deal with uncertainty."

Another view

As we considered Osterholm and Brosseau’s points, we also reached back to Stephen Gire, an Ebola researcher at Harvard University’s Sabeti Lab.

He told us the case for aerosol transmission sketchy at best and he doesn’t believe airborne transmission happens at all.

Gire sent us a diagram of the distance different sized particles travel.

The pink shaded zone shows the known reach of a droplet carrying the Ebola virus (a little over 1 meter). Beyond that short range, transmission is unlikely, Gire said. Gire said many things are theoretically possible, but that doesn’t make them likely. Gire puts any suggestion of airborne transmission in that category.

"It's a nice scientific exercise and something scientist are intrigued to learn more about, but that intrigue doesn't denote a possibility of it occurring in the natural environment," Gire said.

In summary

A new scientific article stated that it is likely that aerosol transmission of Ebola has taken place. That could refer simply to relatively large droplets being expelled from a victim and inhaled by a health care worker. That risk was clear at the height of the Ebola scare. There is no evidence yet that it actually took place, and there is no evidence that points to infection through smaller airborne particles.

A disease like measles spreads through airborne particles that linger in the air. The lead author of the article said that is not what has happened with Ebola.