Lisa M. Brosseau

Thinking about aerosol-transmissible diseases in healthcare settings.

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Why Are Respirators Needed for Healthcare Workers if Ebola is Not Transmitted by Aerosols?

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?

CDC Guidelines

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.

Some Clues?

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:

  1. 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.
  2. Respirators prevent inhalation of small particles, which might contribute to infection if deposited near receptor cells in epithelial tissues.
  3. 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.



A Call for More Collaboration in Treating Ebola Patients: Stop Blaming the Worker

I recently talked with a labor health and safety professional in Canada.  She wanted to know if it made sense to recommend that infection control professionals defer to occupational health and safety professionals in decisions related to worker protection in the on-going response to Ebola in healthcare settings.

Actually, I believe the best approach for both workers and patients is for both of these professions to work together. Both bring important expertise that will ensure everyone’s health is protected.

Infection control professionals know a lot about how to protect patients from infections, but they generally have less knowledge of or focus on protecting workers from patients’ diseases – unless there is a link with patient safety.  On the other hand, occupational health and safety professionals see things from the worker’s perspective first and can help design protocols to assure healthcare worker safety while treating patients.

Occupational health and safety professionals consider how everything in the environment – patients, buildings, materials, processes, work rules, organizational climate, etc. – contributes to worker health.  They make a map of all the process steps, identifying all of the inputs and outputs for each step – including all of the jobs, hazards and exposures – and then identify controls to eliminate the risks.

To address these hazards, occupational health and safety professionals employ a well-established hierarchy when considering and applying controls at each process step.

These proceed from:

  1. Substituting less hazardous materials or equipment to
  2. Isolating the hazard or the worker to
  3. Removing the hazard at its point of generation (e.g. using ventilation) to
  4. Minimizing the frequency of exposure (e.g. rotating jobs) to
  5. Personal protective equipment (PPE)

Note that PPE is the last and least desired form of protection – because it places the burden of control on the employee and has the greatest chance of failure.

For a risk group 4 organism like Ebola, with multiple modes of transmission that are not well-understood, have a high mortality rate and no cure, the hazards can be significant for a healthcare worker at all steps from entry to discharge.

Let’s consider a hospital from the occupational health and safety perspective for the hazard of Ebola virus:

Step 1: Screening

An Ebola patient presenting for treatment to a hospital or clinic will most likely be someone with recent West African travel history who has had close contact with an Ebola-infected individual.

They will come to a hospital emergency room with moderate symptoms that look like those for many other diseases.  If the hospital is prepared, there will be a screening procedure for identifying and quickly isolating suspected Ebola patients.  This is not very different from the initial screening planned for the SARS outbreak or the screening this country has been planning for a novel influenza outbreak.

And it is possible to do this correctly, as was demonstrated in British Columbia during the SARS outbreak (see the SARS Commission reports)  (I’ll return to the story of SARS in Canada in a minute, because it has direct bearing on the role of occupational health and safety professionals in healthcare settings.)

If the focus is on both treating the patient AND protecting the healthcare worker at the point of screening, the latter should be minimizing their contact with the patient and wearing some PPE – depending on the patient’s symptoms and history. Since we don’t know for certain when an Ebola-infected individual becomes infectious, the precautionary approach would suggest PPE that provides full body protection – including respiratory protection.

If screening can be accomplished while in an entirely separate room (e.g. behind a glassed-in reception desk) then the screener would not need any PPE.  At some point, however, someone will need to be in contact with the potentially-infected person, at which point they would need PPE.

Risks & Trade-offs

At this point there are risks and trade-offs. Does the healthcare work conduct a separate risk assessment for each potentially infected patient to determine the right PPE? Or is it better to take the precautionary approach and give the healthcare worker the highest level of PPE possible?

The former would require a whole separate process and training, might not be time- or cost-effective, and could add to the hazard if the wrong decisions are made.  This isn’t a decision that healthcare workers can easily make and would require the input of an occupational health and safety professional.

Besides severe personal risk, it also leaves the worker vulnerable to blame if they make the ‘wrong’ decision.  Unfortunately it is common to blame the worker rather than the process.

To avoid this risk and potential blame, the latter approach then would be the better – take the precautionary approach and give the healthcare worker the highest level of PPE possible.

Step 2: Testing

Hopefully, a suspected Ebola patient is quickly isolated and screening tests are started.  This is an example of “isolating the hazard,” which is at the top of the hierarchy of controls.  And it has the added benefit of limiting exposures of other patients waiting for care, as well as other staff members.

Step 3: Isolation

If the screening tests are positive, the now-confirmed Ebola patient should then be placed in a pre-designated patient care room or negative pressure isolation room.  While it appears that Ebola may not remain alive on surfaces (although the data are very limited), it is able to survive in air for some period of time (see Commentary).

A negative pressure room would ensure that any aerosols generated during patient care would remain within the room and eventually be captured on room air filters.  Patient care rooms, on the other hand, are connected to general ventilation systems and under positive pressure (meaning the air flows away from the room) with no methods for cleaning the air leaving the room.  Given the very little we know about this organism’s modes of transmission, the precautionary approach suggests a negative pressure isolation room would be a better choice – isolating the hazard (the patient and their body fluids and aerosols).

Step 4: Treatment

The number of healthcare workers caring for this patient should be kept to a minimum.  They should have received training well in advance on what to expect for this disease, the PPE required, and the methods for preventing personal infection (proper donning and doffing, cleaning and disinfection of PPE and equipment, etc.).

What type of PPE should be required? 

Because direct contact with body fluids and inhalation of aerosols are both likely modes of transmission, especially as the patient develops more severe symptoms (e.g. vomiting, diarrhea, etc.), healthcare workers should be given the highest levels of PPE that ensure no skin or respiratory system contact while also allowing them to work comfortably.

As Rachael Jones and I discussed in a recent Commentary, the Canadian control banding approach for selecting a respirator indicates that a Powered Air Purifying Respirator (PAPR) with a hood would be a good option.  This has the advantages of covering the head completely and has air flowing into the hood, which ensures both a relatively high level of protection and cooling.  Given the other PPE a healthcare worker will also be wearing (full body coverage with impermeable materials), the cooling features are a big plus.  PAPRs are often employed in biosafety level 3 (BSL3) labs when there is potential exposure to hazardous aerosols.

This appears to be the type of respirator worn by medical professionals at the Nebraska Biocontainment Patient Care Unit.  Dr. Lyon at Emory also describes wearing a PAPR because it allows healthcare workers to work longer and more comfortably and the faceshield doesn’t fog (start watching at 17:00; the PAPR is described at 32:00).

What else is required?

If I were conducting this risk assessment with a hospital I would consult with a biosafety 3 lab or the Nebraska or Emory about their use of PAPRs and their protocols for employee training, proper donning and doffing methods, cleaning and disinfection, maintenance, etc.

But I would also think about employing other control methods from higher on the hierarchy.  We’ve already isolated the hazard (infected patient).  Is there anything we could do to minimize the release of body fluids or aerosols?

There might be different treatment options, equipment or furniture designs, local exhaust ventilation approaches, etc. that would lower the probability or level of exposure.  NIOSH researchers have been exploring new designs for surge capacity negative pressure isolation units, which might be effective at minimizing the amount of aerosol released to the room.  I suspect there are a number of creative solutions that would greatly minimize a healthcare worker’s exposure without compromising patient care.

If I were USAID this would be my “Grand Challenge” as the current Ebola outbreak could easily be repeated in other locations around the world.

What Has Prevented Progress? Learning from the Past

So why haven’t these types of discussions and systematic decision-making taken place?  We’ve known about the Ebola outbreaks in western Africa for several months.  We’ve known there was a chance that Ebola would arrive in the United States since late summer, as the outbreaks worsened.

There are also many occupational health and safety professionals in the United States working for government agencies — OSHA and NIOSH – and elsewhere – who are ready, able and willing to assist with systematic risk assessments.  And there are even a few OHS professionals working in the more innovative and forward-thinking healthcare organizations.

So why are these experts not being included in the discussions? And why have we waited so long to prepare? Here, we can learn something from history – particularly from the story of SARS in Canada.

When the SARS index patient arrived in Vancouver, British Columbia, the treating physician quickly recognized that this person might be infected with SARS and placed the person in isolation.  The result – no SARS outbreak in British Columbia.

When the index patient arrived in Toronto, Ontario the patient was left to wait in a room full of other patients for many hours.  The result – a SARS outbreak.

What was different in these two cities?

As the Honourable Archie Campbell — a noted Canadian jurist investigating how these two cities handled SARS – concluded, the reasons reside with the systems.

In British Columbia there was a close working relationship among public health, infection control and occupational health and safety agencies and professionals.  So the physician who recognized the index patient had been prepared, because occupational health and safety professionals had been included in the planning for a SARS outbreak.

On the other hand, the Toronto public health and occupational health and safety agencies did not have a close working relationship.  Occupational health and safety professionals were excluded from the planning and were never consulted even after the outbreak occurred – which eventually led to a second outbreak when infected individuals were not properly managed. Unfortunately, the investigation shows that the city was more focused on its economic recovery than on correctly managing a public health emergency.

A similar situation applies here in the U.S. to the current Ebola outbreak.  The CDC, although it has within its agency an excellent institute dedicated to the protection of workers (NIOSH) and a laboratory within that institute dedicated to the development and testing of respirators and other PPE (the National Personal Protective Technology Laboratory), has not consulted with or included any of that agency’s or laboratory’s personnel in its decision-making about the U.S. Ebola response.  In fact, it is my understanding that NIOSH and NPPTL personnel have been instructed to remain mute about protecting healthcare workers from Ebola and other infectious diseases.

And, to add further to this bizarre set of circumstances, the USAID – an agency with no expertise in either infection control or occupational safety and health – has determined that the best solution to the western African outbreak is the development of better PPE.  You can be sure that they also never consulted with NIOSH, which has been working tirelessly for many years and in collaboration with manufacturers and other stakeholders, to develop better PPE for healthcare workers.  For exactly this type of situation!

What is to be done?

It is easy to blame the workers for getting infected, and even to blame the CDC and the federal government for failing to conduct the type of planning and decision-making that would have ensured better preparation and protection for healthcare workers.

We don’t need more blame. We don’t need better PPE.  We need better decision making going forward, and that will only happen with better collaboration among all of the experts.

Occupational health and safety professionals and their federal and state agencies – OSHA and NIOSH- should be invited to work in collaboration with infection control specialists and public health professionals to assure the right controls are in place and the right decisions are made to protect both health care workers AND patients.

Healthcare workers should be agitating for better protection, but they should also be calling on their governments – local, state and federal – to utilize the resources of OSHA and NIOSH and requesting that their organizations engage occupational health and safety professionals.  And if there isn’t an occupational health and safety professional at hand, they should be agitating for their inclusion and a collaborative approach between all the players to develop the best solutions for everyone – patients and healthcare workers.


Is It Time To Declare Ebola an Aerosol-Transmissible Disease Requiring a Respirator?

My recent Commentary published on the CIDRAP website discussed whether Ebola could be an aerosol-transmissible disease.  My colleague and I described a number of features of an organism that would make it aerosol-transmissible.

After we published this Commentary, however, it quickly became clear that many people struggled with the notion that infectious organisms could be transmitted by aerosols located near a source.  And it was clear that they didn’t agree with our argument that the standard infection control paradigm of “droplets” and “airborne” doesn’t fit with current knowledge about aerosols.

After trying unsuccessfully to get the Pro-Med website to publish a follow-up to our Commentary, Dr. Raina MacIntyre posted our further explanation of aerosols on her Infectious Diseases Blog at the University of New South Wales.

I would like to thank the many people who have written and called me about these posts.

But it seems that further details and repetition are necessary, as the blogosphere seems intent on disparaging the term “aerosol” in favor of almost anything else – including new terms with no scientific meaning.

So the goal of this blog is to explain, once again, what I – and many other scientists  – mean when we use the term “aerosol.”

First, I must note that the word “aerosol” is not an “esoteric” or unusual term — in fact, there is a whole society dedicated to the study and use of aerosols:  the American Association of Aerosol Research (, which was founded in 1982 by a group of renowned scientists.  I recommend visiting the AAAR website, where you will discover that this organization plays an important role in fields as diverse as toxicology, air quality, atmospheric science, pharmaceuticals, new materials development, etc.

What aerosol scientists have found is that when a liquid such as blood, urine, vomit, mucus, etc. is emitted with force, a liquid spray aerosol is created.  Sprays generally contain particles in a wide range of sizes.   They are created by applying a force that breaks a liquid into small particles that are dispersed into the air.  Sprays are used in a lot of applications — coating surfaces (e.g. spray painting cars), delivering drugs (e.g. asthma inhalers), using cosmetics (e.g. hair spray).  And sprays are created by a lot of human processes (e.g. coughing, sneezing, diarrhea, vomiting) and medical procedures (e.g. bronchoscopy, intubation, etc.).

Spray aerosols undergo a number of simultaneous processes:

  1. The liquid (water) portion evaporates (very quickly), which means, overall, the aerosol will consist of smaller particles than when it was first created. This happens within milliseconds, while the aerosol is still near its source. The result – inhalable particles near the source (patient) and in the breathing zone of a healthcare worker.
  1. All of the particles will begin falling toward the ground (some more quickly than others depending on their aerodynamic diameter, which is determined by size, shape and density). This doesn’t mean, however, that most of the particles will immediately drop to the ground – as we often hear from infection control professionals who insist that the big “droplets” near a source will rapidly fall to the floor. That will only happen for the very large particles.  Many of the particles in a spray aerosol will continue to be suspended in the air for many minutes or hours as they are slowly settling due to gravity.  The result – inhalable particles near a patient and in the breathing zone of a healthcare worker.
  1. Particles are picked up by air currents and travel along with these currents. In most rooms, the travel of air will be from the air inlet (often in the ceiling) to air outlets near the floor. This type of ventilation is supposed to result in a well-mixed air space, dilution of gas and particle concentrations, and removal of unwanted contaminants.  In most cases, however, there will be “short-circuiting,” which means that particles can remain suspended for lengthy periods of time in pockets of air that are not well-mixed.  This means that some particles (especially the smaller ones) could remain suspended in air near their source well beyond their gravitational settling time.  The result – inhalable particles near a patient and in the breathing zone of a healthcare worker.
  1. Very small particles will be bombarded by air molecules, which causes them to move randomly and eventually disperse throughout a space – this is called diffusion. The result – smaller inhalable particles distributed throughout a room, including near a patient — and in the breathing zone of a healthcare worker.


So, it should be clear that the “droplet” and “airborne” paradigm just doesn’t cut it.  The big particles don’t just drop to the ground.  And the small particles don’t rapidly travel to the far reaches of the room.  Close exposure to small particles is not only possible, it is likely the cause of frequent disease transmission.

The question to ask someone who insists that a disease will only be transmitted by “direct contact” is — how do they know?  Because you can’t tell the difference between an infection that is transmitted by a droplet “propelled” directly into the nose or deposited from the hand into the mouth — and one that is inhaled into the nose or mouth when standing near the source of a spray aerosol.  Let’s say that again — there is no human epidemiology study that is going to elucidate which of these modes of transmission is responsible for an infection.

So how do we know that some diseases are able to transmit disease through inhalable particles?  In the case of tuberculosis, although scientists conjectured that aerosols might be responsible for disease transmission, it was only after a series of innovative animal experiments by Dr. William Firth Wells that we had incontrovertible evidence for aerosol transmission.

In other cases, everyone in a space – both near and far – was infected by a single person with the disease.  This has been shown for measles and norovirus, neither of which results in a respiratory infection.  While we know these diseases are aerosol-transmissible, we don’t entirely understand HOW they accomplish transmission.  Meaning – we don’t know very much about the exact source of the aerosol or how that aerosol causes disease in a nearby person.

Clearly, generating an aerosol and inhaling an infectious organism are only two parts of the puzzle about aerosol-transmissible diseases.  Dr. Jones and I discussed other types of evidence for aerosol transmission of Ebola in our Commentary, including the viability of the organism in air at room temperature and humidity, receptors for the organism in epithelial tissues, animal data showing infection via aerosols and scientific reports of aerosol transmission from one non-human primate species to another.   All of these FACTS contribute to the evidence that Ebola is an aerosol-transmissible disease.

I will explore this topic in later posts.

The key messages I wish to emphasize here are:

  1. Liquid aerosols (sprays) create particles of all sizes that can easily persist near the source and can be easily inhaled by someone standing near the source.
  1. There is no easy way to tell the difference between transmission that occurs by “direct contact” (with droplets or via hands) and aerosol inhalation.


What does this mean for Ebola virus disease?

The risk factors for Ebola – caring for an infected person, sharing a bed, funeral activities, and contact with blood or other body fluids – do not rule out aerosol inhalation in favor of any other type of disease transmission.  All of these could include nearby exposure to liquid sprays, which could be inhaled.  So the best we can conclude from these risk factors is that the modes of transmission include direct contact AND aerosol inhalation.

And if this is the case, then a respirator is the only option for protecting healthcare workers from Ebola aerosols.

It is time for CDC and WHO to give serious consideration to aerosols as a route of transmission for Ebola – and stop blaming healthcare worker infections on their failure to follow protocols.  Instead, the blame rests with organizations that can’t let go of an incorrect paradigm and recognize that their protocols are inadequate and will not protect healthcare workers from exposure to infectious aerosols.

In the meantime, I strongly urge healthcare workers to insist on respirators and training in how to use and wear them for all encounters with Ebola or suspected-Ebola patients.