Both Osterholm and Heymann note that virologists are extremely hesitant to discuss the possibility of discussing the possibility and potential for Ebola to become an airborne virus because they are scared to death of being professionally discredited and accused of whipping up hysteria with regard to the dangers posed by the present Ebola outbreak. However, in private, they both state, that anyone close to the virus are expressing grave fears about this possibility. In fact, Osterholm specifically stated in the New York Times article that … it’s something they are “definitely considering in private.”
It's unclear how the woman became infected, but MSF teams are investigating the contamination as part of standard procedures, the group said.
COMMENTARY: Health workers need optimal respiratory protection for Ebola
- No proven pre- or post-exposure treatment modalities
- A high case-fatality rate
- Unclear modes of transmission
How are infectious diseases transmitted via aerosols?
Is Ebola an aerosol-transmissible disease?
What do we know about Ebola transmission?
Which respirator to wear?
- Identify the organism's risk group (1 to 4). Risk group reflects the toxicity of an organism, including the degree and type of disease and whether treatments are available. Ebola is in risk group 4, the most toxic organisms, because it can cause serious human or animal disease, is easily transmitted, directly or indirectly, and currently has no effective treatments or preventive measures.
- Identify the generation rate. The rate of aerosol generation reflects the number of particles created per time (eg, particles per second). Some processes, such as coughing, create more aerosols than others, like normal breathing. Some processes, like intubation and toilet flushing, can rapidly generate very large quantities of aerosols. The control banding approach assigns a qualitative rank ranging from low (1) to high (4) (eg, normal breathing without coughing has a rank of 1).
- Identify the level of control. Removing contaminated air and replacing it with clean air, as accomplished with a ventilation system, is effective for lowering the overall concentration of infectious aerosol particles in a space, although it may not be effective at lowering concentration in the immediate vicinity of a source. The number of air changes per hour (ACH) reflects the rate of air removal and replacement. This is a useful variable, because it is relatively easy to measure and, for hospitals, reflects building code requirements for different types of rooms. Again, a qualitative ranking is used to reflect low (1) versus high (4) ACH. Even if the true ventilation rate is not known, the examples can be used to select an appropriate air exchange rate.
- Identify the respirator assigned protection factor. Respirators are designated by their "class," each of which has an assigned protection factor (APF) that reflects the degree of protection. The APF represents the outside, environmental concentration divided by the inside, facepiece concentration. An APF of 10 means that the outside concentration of a particular contaminant will be 10 times greater than that inside the respirator. If the concentration outside the respirator is very high, an assigned protection factor of 10 may not prevent the wearer from inhaling an infective dose of a highly toxic organism.
Implications for protecting health workers in Africa
Adequate protection is essential
- Patients and procedures generate aerosols, and Ebola virus remains viable in aerosols for up to 90 minutes.
- All sizes of aerosol particles are easily inhaled both near to and far from the patient.
- Crowding, limited air exchange, and close interactions with patients all contribute to the probability that healthcare workers will be exposed to high concentrations of very toxic infectious aerosols.
- Ebola targets immune response cells found in all epithelial tissues, including in the respiratory and gastrointestinal system.
- Experimental data support aerosols as a mode of disease transmission in non-human primates.
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