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Explaining aerosol transmission of Ebola

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  • Explaining aerosol transmission of Ebola

    Explaining aerosol transmission of Ebola
    Professor Lisa Brousseau
    By Professor Lisa Brousseau and Dr Rachel Jones, University of Illinois at Chicago.

    September 24 2014

    I would like to respond to recent comments about the likelihood of aerosol transmission of Ebola virus. The CIDRAP commentary I published with my colleague, Dr. Rachael Jones outlines the variables that might contribute to aerosol transmission of this particular infectious organism in healthcare settings. It is important to clarify that our use of the term "aerosol transmission” is not synonymous with the traditional definition of "airborne transmission,” i.e., transmission via inhalation of infectious particles small enough to travel on air currents and infect persons at some distance (and time) from the infectious person. Instead of remote inhalation exposure , we consider the more general mechanism of aerosol transmission, which encompasses aerosolized infectious particles of many sizes that are able to infect persons upon inhalation, inspiration or projection, at a variety of distances from the infectious source. While aerosol emission from the respiratory tract is more familiar, epidemiological and experimental studies conducted over several decades have demonstrated that infectious aerosols may be generated by vomiting and diarrhea, particularly toilet flushing. These aerosols can be inhaled and/or ingested by susceptible people close to an infectious person or the emission event. Surgical masks have been shown in laboratory and field studies to offer insufficient protection against the penetration of small infectious particles to the respiratory tract.

    In the commentary, we described the role that short-range transmission of aerosols from vomiting and diarrhea might play in Ebola virus transmission. While we mentioned coughing and sneezing as possible modes of aerosolization of infectious organisms, in general, these modes are likely to be less important for Ebola virus than for pathogens that primarily cause respiratory infections. Organisms that disperse via aerosols from diarrhea and vomiting may or may not result in infectious in crowded public spaces: This may not observed if the inhabitants can easily leave the space after an emission. Examples of this behavior, however, exist. Norovirus, for example, can be dispersed via vomiting or diarrhea in crowded public spaces, like airplanes and cruise ships.

    There is clear evidence of Ebola virus being spread from a very sick individual in Nigeria following short contact times without reported droplet spray. It is these facts that led us to conclude that Ebola virus may an opportunistic aerosol transmissible organism. The opportunity for aerosol transmission is especially high in a healthcare setting, where workers engage with symptomatic patients and perform medical procedures that generate aerosols.

    Dismissing the possibility of aerosol transmission on the basis of lack of respiratory spread in crowded spaces fails to recognize that aerosols can be created in many other ways, and fails to acknowledge that persons have become infected with Ebola virus without being exposed to the blood or body fluids of infectious patients via direct contact. Ultimately, the tissues of a susceptible person cannot distinguish whether the virus arrived by way of contaminated hands - as in contact transmission, by way of projected droplets - as in droplet transmission, or by way of inhaled aerosol; and the mucous membranes of the nose and mouth are readily accessed through all mechanisms.

    Dr Brosseau is a Professor and Dr Jones an Assistant Professor in the School of Public Health, Division of Environmental and Occupational Health Sciences, at the University of Illinois at Chicago. This was first posted on Promed Mail in response to the CIDRAP article.
    "We are in this breathing space before it happens. We do not know how long that breathing space is going to be. But, if we are not all organizing ourselves to get ready and to take action to prepare for a pandemic, then we are squandering an opportunity for our human security"- Dr. David Nabarro

  • #2
    Re: Explaining aerosol transmission of Ebola

    Assessing the Science of Ebola Transmission

    As leading Ebola virologist Heinz Feldmann recently said, the discussion of Ebola prevention “should be fact-based; it should be data-based.” Interpretation of those facts and data is often clouded by politics and opinion. But they are not as ambiguous as debates in media have made them seem.

    Earlier this week, The Atlantic ran an interview on the current Ebola epidemic with Steven Hatfill, a former employee of the U.S. Army Medical Research Institute of Infectious Disease (USAMRIID) who is famous for being wrongly accused of the 2001 anthrax attacks. Hatfill, presented as a world-leading expert on Ebola virus, gave his perspective on topics ranging from transmission of the virus to preparedness for an outbreak in the United States. Some of Hatfill’s concerns about our preparedness to stamp out outbreaks quickly are sound, but the bulk of the interview, about the virus and the disease it causes, goes well beyond the data.

    The misinterpretations and misrepresentations of data that Hatfill espouses can be found in many places online, and especially on TV. In light of this, we can’t be surprised so many Americans really don’t know what to think and who to believe on Ebola. Going point-by-point through an interview is boring, unnecessary, and would make Hatfill the core issue. He isn’t. Misrepresentations of the scientific literature on Ebola aren’t unique to him. But I picked some of the most common and dangerous misrepresentations he upheld and dug into the primary scientific literature.

    The most controversial part of the ongoing Ebola discussion has been the question of transmission, namely, whether it spreads by an airborne route. Other people have painfully detailed the differences between airborne, aerosol, and droplet transmission. That’s not my interest, or area of expertise. The question that people have, I think, is whether Ebola spreads like the flu; whether they can get it by breathing the same air as someone who has it. The biggest obstacle to clearly communicating the answer to this question, which is no, is the misinterpretation of a 2012 study in which Ebola virus was transmitted from pigs to monkeys without direct contact.
    Twitter: @RonanKelly13
    The views expressed are mine alone and do not represent the views of my employer or any other person or organization.