CDC adds respirators, clarifies confusing issue of droplet, aerosol and airborne transmission
Rigorous step-by-step approach recommended for donning, removal of PPE
An issue that has caused considerable confusion and fear during the Ebola outbreak is the difference between airborne, aerosol and droplet transmission. There are clear differences, but they weren’t elucidated particularly well at the onset of Ebola cases in the U.S., leaving the public uninformed and then panicked when some reputable scientists warned that there was a small chance the Ebola virus could mutate and spread like a truly airborne pathogen such as measles.
"When I hear people talk about this going airborne — some very well-known people have made that comment — that is a giant leap," says Eddie Hedrick MT(ASCP), CIC, project coordinator in the state Bureau of Communicable Disease Control & Prevention in in Columbia, MO.
"Although viruses mutate, they mutate to evolve through natural selection and that kind of thing," he says. "They really don’t suddenly change how they are transmitted. For that to happen would take changes not just in genetic characteristics but changes in physical characteristics that are well beyond the organism’s ability. For the virus to stay in the air for long periods of time it would have to be able to survive by itself in a dried state. It really doesn’t do that very well."
While emphasizing that Ebola does not spread by the airborne route (e.g., tuberculosis), the Centers for Disease Control and Prevention recently revised its infection control guidelines and recommended that health care workers wear N95 respirators or powered air purifying respirators (PAPRs) for treating patients stricken with the deadly virus.
"We are recommending either of those options — but not a face mask." said CDC Director Tom Frieden, MD, MPH. "That’s not because we think that Ebola is airborne, but rather because we think that [procedures] in American hospitals can be so risky, whether that is suctioning or intubation or other things that may not be done in other parts of the world such as Africa. We want to add the extra margin of safety."
The CDC previously recommended that respiratory protection and negative pressure rooms should be used if a procedure that may generate aerosols is being conducted on an Ebola patient. (i.e., bronchoscopy, sputum induction, intubation and extubation, and open suctioning of airways.) In such cases the fine mist of the aerosol, possibly including infective virus from the patent may be inhaled if the worker is unprotected.
Respiratory protection was one of the bigger points of discussion in the development of the new "consensus" guidelines for Ebola personal protective equipment (PPE), which included input from clinicians who treated Ebola patients at Emory University Hospital, Nebraska Medical Center and the National Institutes of Health Clinical Center, he said.
Though it was starting to appear that many hospitals were going to err on the side of caution and use respirators regardless, the CDC argued in earlier Ebola guidelines that a surgical mask and face shield were sufficient to contain contact and droplet spread of the virus unless procedures were likely to generate aerosols that could be inhaled. Despite persistent questions, concerns and the occasional conspiracy theory, the CDC held to that recommendation for months.
The agency was likely trying to head off public misperceptions — and the ensuing high anxiety — that Ebola could transmit through the air. That is still not the case, but health care workers could use as much reassurance as possible if they are going to be asked to walk into the isolation room of an Ebola patient. A single exposure could mean death. And as a practical matter, the old guidelines could lead to situations where clinicians may decide the patient could benefit from an aerosol-generating procedure, but they would have to leave the room and re-garb to don a respirator.
"We don’t want the health care worker who is already suited up — and it takes a while to suit up — saying, [I need] to suction this patient and that might [create] aerosol generation, so I’m going to leave — take all of this off — and put on an N95 or PAPR and come back,’" Frieden said. "So we’ve [decided] that we are not going to recommend that face masks be used, but either N95s or PAPRs. For other countries [in Africa] that may be less relevant, but it’s because of the kind of [aerosol generating] procedures that are done here."
CDC Q&A: What is the difference between airborne and droplet
The Centers for Disease Control and Prevention provides these answers to commonly asked questions about Ebola transmission:
Is Ebola airborne? Ebola is not a respiratory disease and is not spread through the airborne route.
Can Ebola be spread by coughing or sneezing? There is no evidence that Ebola is spread by coughing or sneezing. Ebola is transmitted through direct contact with the blood or body fluids of a person who is sick with Ebola; the virus is not transmitted through the air (like measles virus). However, large droplets (splashes or sprays) of respiratory or other secretions from a person who is sick with Ebola could be infectious, and therefore certain precautions (standard, contact, and droplet precautions) are recommended for use in healthcare settings to prevent the transmission of Ebola from patients to healthcare personnel and other patients or family members.
Is Ebola spread through droplets? To get Ebola, you have to directly get body fluids (blood, diarrhea, sweat, vomit, urine, semen, breast milk) from someone who is sick with Ebola in your mouth, nose, eyes or through a break in your skin or through sexual contact. That can happen by being splashed with droplets, or through other direct contact, like touching infectious body fluids. Healthcare providers caring for Ebola patients and the family and friends in close contact with Ebola patients are at the highest risk of getting sick when they touch or are splashed by infectious blood or body fluids from a sick patient.
What’s the difference between infections spread through the air or by droplets? Airborne spread happens when germs float through the air after a person talks, coughs, or sneezes. Those germs can be inhaled even after the original person is no longer nearby. Direct contact with the infectious person is NOT needed for someone else to get sick. Germs like chicken pox and TB are spread through the air.
Droplet spread happens when fluids in large droplets from a sick person splash the eyes, nose, or mouth of another person or through a cut in the skin. Droplets may cause short-term environmental contamination, like a soiled bathroom surface or handrails, from which another person can pick up the infectious material. Germs like plague can be spread through large droplets. Ebola might be spread through large droplets but only when a person is very sick."
Ritual removal of PPE
The new CDC guidance focuses on specific PPE that health care workers should use, providing detailed instructions on how to remove equipment safely.
"The greatest risk in Ebola care is in the taking off of whatever equipment the health care worker has put on" Frieden said. "One of the critical aspects of these guidelines is a very structured way of doing that step-by-step which is supervised, and in a way ritualized, so that it is done the same way every time."
The CDC Ebola guidelines are centered on three principles:
All healthcare workers undergo rigorous training and are practiced and competent with PPE, including taking it on and off in a systematic manner
No skin exposure when PPE is worn
All workers are supervised by a trained monitor who watches each worker taking PPE on and off. This is to ensure each worker follows the step by step processes, especially to disinfect visibly contaminated PPE. The trained monitor can spot any missteps in real-time and immediately address them.
The CDC is essentially recommending the same PPE included in its August 1, 2014 guidance, with the addition of respirators, coveralls and single-use, disposable hoods and face shields. Goggles are no longer recommended, as they may not provide complete skin coverage in comparison to a full face shield. Additionally, goggles are not disposable, may fog after extended use, and healthcare workers may be tempted to manipulate them with contaminated gloved hands, the CDC noted. The CDC is recommending an extensive ritual for donning and removing PPE that will take some practice to learn, and should be done in the presence of a trained observer when actually treating an Ebola patient. A video demonstration of how to safely don PPE gear and remove it after contact with Ebola patients is available at: http://bit.ly/13HBkTb
The new CDC recommendations for PPE use by health care workers caring for Ebola patients include:
Double gloves
Boot covers that are waterproof and go to at least mid-calf or leg covers
Single use fluid resistant or impermeable gown that extends to at least mid-calf or coverall without integrated hood.
Respirators, including either N95 respirators or powered air purifying respirator (PAPR)
Single-use, full-face shield that is disposable
Surgical hoods to ensure complete coverage of the head and neck
Apron that is waterproof and covers the torso to the level of the mid-calf should be used if Ebola patients have vomiting or diarrhea.
Editor’s note: The CDC infection control guidelines for Ebola are available at http://1.usa.gov/10ixUos
