As the debate continues about how Ebola Virus Disease (EVD) might be transmitted from one person to another, it’s important to note that the CDC guidelines for healthcare worker protection include recommendations for respiratory protection from aerosols.
However, CDC also insists that Ebola can only be transmitted by direct contact with the bodily fluids of an infected person and can never be transmitted by the airborne route.
If the only way to transmit infection is by direct contact, wouldn’t a surgical mask and faceshield provide adequate protection from aerosol droplets? [Infection control and medical professionals have often told me that N95 filtering facepiece respirators won’t protect the wearer from splashes, because, unlike surgical masks, they aren’t tested for blood penetration. I doubt this is true, but I don’t know of any studies that support or refute this.]
Alternatively, if whole-head droplet protection is needed, wouldn’t a surgical hood be adequate?
Why are respirators needed if Ebola can’t be transmitted by inhalation?
The most recent (October 20, 2014) CDC guidance on personal protective equipment (PPE) for healthcare workers during management of patients with Ebola Virus Disease (EVD) states that:
“In healthcare settings, Ebola is spread through direct contact (e.g., through broken skin or through mucous membranes of the eyes, nose, or mouth) with blood or body fluids of a person who is sick with Ebola or with objects (e.g., needles, syringes) that have been contaminated with the virus.”
The guidance states, however, that:
“CDC recommends facilities use a powered air-purifying respirator (PAPR) or an N95 or higher respirator in the event of an unexpected aerosol generating procedure.”
The narrator of a CDC video “Respiratory Protection for Ebola” assures us that “Ebola is not transmitted via an airborne route” and that “healthcare workers have safely cared for patients with Ebola over several decades wearing surgical masks instead of respirators.” However, he also explains that respirators are recommended for healthcare workers because an aerosol-generating procedure, such as intubation, could occur at any time and correct donning can take time.
For aerosol-generating procedures (AGPs) with EVD patients the CDC hospital infection prevention and control guidelines recommend:
- Avoid AGPs for patients with EVD.
- If performing AGPs, use a combination of measures to reduce exposures from aerosol-generating procedures when performed on Ebola HF [hemorrhagic fever] patients.
- Visitors should not be present during aerosol-generating procedures.
- Limiting the number of HCP [health care personnel] present during the procedure to only those essential for patient-care and support.
- Conduct the procedures in a private room and ideally in an Airborne Infection Isolation Room (AIIR) when feasible. Room doors should be kept closed during the procedure except when entering or leaving the room, and entry and exit should be minimized during and shortly after the procedure.
- HCP should wear appropriate PPE during aerosol generating procedures.
This CDC infographic about Ebola transmission for the general public offers one clue: “Ebola is not a respiratory disease and is not spread through the airborne route.”
It seems to be a common misunderstanding that airborne transmission is only possible for organisms that cause respiratory disease.
The 2007 Healthcare Infection Control Practices Advisory Committee (HICPAC) guidelines include non-respiratory diseases in the definition of airborne transmission:
“…dissemination of either airborne droplet nuclei or small particles in the respirable size range containing infectious agents that remain infective over time and distance (e.g., spores of Aspergillus spp, and Mycobacterium tuberculosis). Microorganisms carried in this manner may be dispersed over long distances by air currents and may be inhaled by susceptible individuals who have not had face-to-face contact with (or been in the same room with) the infectious individual….Infectious agents to which this applies include Mycobacterium tuberculosis, rubeola virus (measles), and varicella-zoster virus (chickenpox)….For certain other respiratory infectious agents, such as influenza and rhinovirus, and even some gastrointestinal viruses (e.g., norovirus and rotavirus) there is some evidence that the pathogen may be transmitted via small-particle aerosols, under natural and experimental conditions.”
The 2007 HICPAC guidelines offer some additional clues to the on-going confusion about airborne transmission:
“In contrast to the strict interpretation of an airborne route for transmission (i.e., long distances beyond the patient room environment), short distance transmission by small particle aerosols generated under specific circumstances (e.g., during endotracheal intubation) to persons in the immediate area near the patient has been demonstrated. Also, aerosolized particles <100 μm can remain suspended in air when room air current velocities exceed the terminal settling velocities of the particles. SARS-CoV transmission has been associated with endotracheal intubation, noninvasive positive pressure ventilation, and cardiopulmonary resuscitation. Although the most frequent routes of transmission of noroviruses are contact and food and waterborne routes, several reports suggest that noroviruses may be transmitted through aerosolization of infectious particles from vomitus or fecal material. It is hypothesized that the aerosolized particles are inhaled and subsequently swallowed.”
In a new Commentary co-authored with Dr. Rachael Jones, we suggest that a new infection control paradigm might resolve this confusion by replacing “droplet” and “airborne” transmission with “aerosol transmission.”
A Rationale is Needed
What’s missing from the CDC guidelines is a rationale for recommending respirators for protection during aerosol-generating procedures.
There is an easy explanation that wouldn’t add to public anxiety. I recommend that CDC add the following to their guidance:
- In addition to some medical procedures, vomiting, diarrhea, coughing, sneezing and other natural processes should be considered aerosol-generating procedures that can create high aerosol concentrations that include small inhalable particles and large droplet sprays.
- Respirators prevent inhalation of small particles, which might contribute to infection if deposited near receptor cells in epithelial tissues.
- A respirator that includes a full-facepiece or hood (such as an elastomeric or powered air purifying respirator) offers a higher level of small particle inhalation protection than an N95 filtering facepiece respirator and offers more skin and mucous membrane protection from the impact of large aerosol droplets.
It is very unlikely that the general public will ever come in contact with someone experiencing severe and advanced symptoms that generate aerosols. But healthcare and other workers might be exposed to someone experiencing advanced symptoms or the aerosols created by these symptoms.
That’s why healthcare and other workers need respirators for Ebola Virus Disease and the general U.S. public doesn’t.