Sunday, October 12, 2014

Is Ebola airborne?*

Regarding my upcoming trip to Liberia, I suspect that there are people who are concerned about not only my safety, but also the safety of my family and my community. I adore my wife and son and would not have chosen to work as an Ebola Response Clinician unless I believed that I could do so safely and without leaving Holly without a husband and Andrew without father or, unthinkably, exposing either of them to a highly lethal virus.

From hearing people's comments in the media and from some of the phone calls we have received at the health department, it seems to me that there is a lot of confusion about the means by which ebolaviruses are transmitted. Although I addressed Ebola transmission in the presentation I gave to the Pierce County Medical Reserve Corps, I'd like to go into more detail about the question of whether ebolaviruses are transmitted by the airborne route.

The Centers for Disease Control and Prevention, the World Health Organization, and every textbook chapter on Ebola virus disease (EVD) that I have read acknowledge that there is a risk of ebolavirus transmission through respiratory droplets, which are expelled when a person coughs or sneezes. At the same time, all of those sources state that there is no evidence that ebolaviruses are transmitted from person-to-person by the airborne route. That may seem like a contradiction, but the difference is in the size of the droplets.

Coughing and sneezing generates large respiratory droplets that fall out of the air within a few feet. Transmission through large droplets usually requires close contact. These droplets can come in contact with the eyes or be inhaled and trapped in the upper airway: the nose, mouth, pharynx, trachea, and bronchi.

NCI, 2012
Pertussis and influenza are examples of diseases that are transmitted by large respiratory droplets. These large droplets can be blocked by wearing a simple surgical mask – the type you can buy at your local drug store.

Airborne transmission refers to pathogens that are carried by droplet nuclei, particles that are 1 to 5 micrometers (μm) in diameter. These particles can remain suspended in the air for hours and can pass through the upper airway into the alveoli.

Droplet nuclei are not blocked by surgical masks and require high-efficiency particulate air filtration (HEPA) for protection. In a health care setting, these are usually N95 masks or a powered air-purifying respirator (PAPR). Mycobacterium tuberculosis, the bacteria that causes tuberculosis, is an example of a pathogen that is transmitted by the airborne route.
Powered air-purifying respirator (PAPR)
Measles is another example of a disease that is transmitted by the airborne route. This year in Pierce County we had two public measles exposures that required the health department to notify the public of where and when a person with measles had been.
Because the small particles that transmit measles can remain suspended in the air for hours, we recommend that people who were in a place at the time a person was measles was there and two hours after either ensure that they are either immune to measles or receive a dose of MMR.

Another important difference between measles and ebolaviruses is that people with measles are contagious up to 4 days before showing symptoms of the disease. A person with EVD cannot transmit the virus until she or he is symptomatic.

A number of people have raised concerns over the adequacy of surgical masks to prevent health care workers frombeing infected with Ebola. Adding to the confusion, it appears that there is airborne transmission of Reston ebolavirus (which does not cause disease in humans) between non-human primates and Zaïre ebolavirus has been transmitted between non-human primates under experimental conditions. Michael Osterholm raised the question of whether Zaïre ebolavirus, the species causing the current epidemic in West Africa, could mutate to become airborne.

It is very distressing that several health care providers working in the Ebola epidemic in West Africa have become infected and developed EVD. We don't know the circumstances under which they became infected. It's important to realize that there are hundreds of expatriate health workers in West Africa so, although it certainly gives us reason for concern, those providers are a small proportion of the total those who have worked and continue to work in clinical settings in West Africa.

As I mentioned in my last post, my first stop will be Atlanta to receive safety training at the CDC. Once I return to the U.S., I will monitor my temperature twice daily and report any symptoms suggestive of EVD to the local health authority; that is, the very office where I work!

I intend to take every precaution to protect myself, my family, and my community.

I appreciate the support and prayers from my family, friends, and colleagues.

I encourage other health care providers to consider volunteering your time to help end this epidemic.

Blumberg, L., Enria, D., & Bausch, D. G. (2014). Viral hemorrhagic fevers. In J. Farrar, P. J. Hotez, T. Junghanss, G. Kang, D. Lalloo, & N. J. White (Eds.) Manson's tropical diseases, 23rd Ed. [Electronic version]. Elsevier.

Brosseau, L. M. & Jones, R. (Sept. 17, 2014). Commentary: Health workers need optimal respiratory protection for Ebola.

Centers for Disease Control and Prevention. (2014). Infection prevention and control recommendations for hospitalized patients with known or suspected Ebola virus disease in U.S. hospitals.

Geisbert, T. W. (2014). Marburg and Ebola hemorrhagic fevers (Filoviruses). In J. E. Bennett, R. Dolin, & M. J. Blaser (Eds.). Mandell, Douglas, and Bennett's principles and practice of infectious diseases, 8th Ed. [Electronic version]. Elsevier.

Hartman, A. L. (2013). Ebola and Marburg virus infections. In, A. J. Magill, D. R. Hill, T. Solomon, & E. T. Ryan (Eds.) Hunter's tropical medicine, 9th Ed. [Electronic version]. Elsevier.

Osterholm, M. T. (Sept. 11, 2014). What we're afraid to say about Ebola.

World Health Organization. (2014). What we know about transmission of the Ebola virus among humans.

*Betteridge's law: Any headline which ends in a question mark can be answered by the word no.


1 comment:

  1. good luck to you - one thing I agree that I've heard is that if we don't stop Ebola in Africa than it will be here to stay, like pertussis and influenza