School of Public Health and Community Medicine

Explaining aerosol transmission of Ebola

Professor Lisa Brosseau

By Professor Lisa Brosseau and Assistant Professor Rachael 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.

CIDRAP commentary: http://www.cidrap.umn.edu/news-perspective/2014/09/commentary-health-workers-need-optimal-respiratory-protection-ebola

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 result in infections in crowded public spaces: This may not be 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.  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. 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.

 

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.

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