Beyond fit-testing: Why can’t health care workers just use surgical masks?
CDC guidance sparks controversy over protection
If terrorists spread pneumonic plague in your community, will surgical masks be sufficient to protect health care workers? That question has renewed a controversy over respiratory protection, this time whether surgical masks are appropriate for some diseases while fit-tested N95 filtering facepiece respirators are required for others.
As part of a national bioterrorism exercise, the Centers for Disease Control and Prevention (CDC) issued interim guidance on plague that said surgical masks would provide adequate protection but that the additional protection provided by N95s would be “prudent.”
The guidance also noted that “exigent circumstances” during a large-scale event might require suspension of fit-testing and medical clearance requirements.
Labor unions responded swiftly with a letter to CDC director Julie L. Gerberding, MD, MPH, stating: “This guidance, if followed, would put health care workers at risk of serious and potentially deadly exposure. We ask that this inaccurate and harmful document be withdrawn immediately.”
The CDC did withdraw the interim guidance, but not just because of the union response, says Von Roebuck, spokesman. The guidance “was placed on the CDC web site to gather additional input and information” during the exercise, he says. “CDC removed the interim guidance after the training exercise ended and after receiving a variety of comments. The interim guidance was not removed from the web site because of one specific complaint or comment.”
The CDC recommends surgical masks as a part of droplet precautions for certain diseases, such as influenza, pertussis, and naturally occurring plague, yet recommends a respirator for severe acute respiratory syndrome (SARS) and avian influenza.
In its draft isolation guidelines, which are undergoing revision, the CDC offers no recommendation on whether to use a surgical mask or a respirator for exposure to measles and varicella.1
Not surprisingly, in the front lines of occupational health in hospitals where employee health professionals are trying to protect health care workers but function under financial constraints, confusion reigns.
“In the real world of health care delivery, health care is imploding under technical and economic burdens,” says Michael Hodgson, MD, MPH, director of occupational health programs for the Veterans Health Administration in Washington, DC.
Is annual fit-testing really necessary? Who should be fit-tested? When should you use an N95? There are little scientific data that link the protective properties of masks and respirators with the transmissibility of different diseases. And of course, there’s the practical difficulty of following disease-specific guidelines when presented with a coughing patient. Is it pertussis? Tuberculosis? Pneumonic plague? Avian influenza?
“In the current national scene, there’s unwillingness to say clearly what we think, to face the risk,” says Hodgson. “[CDC experts] don’t give real guidance to us in a way we can act and justify in the way we need to.”
“Tuberculosis, for example, has all but disappeared despite the absence of annual fit-testing, because of the effectiveness of other program elements,” he says. “Does adding the cost of annual fit-testing, resources taken from other safety programs, meaningfully improve health care safety?”
Droplet vs. airborne precautions
The CDC’s recommendations on protective equipment are based on mode of transmission. Droplet precautions are triggered when a health care worker has close contact (3 feet or fewer) with a patient known or suspected to be infected with diseases spread by respiratory droplets.
The large droplets do not remain suspended in the air, explains Denise Cardo, MD, director of CDC’s Division of Health Care Quality Promotion. They may fall to a surface, creating a risk of surface contamination and making hand hygiene an important factor in transmission, she says.
By contrast, with an airborne disease such as TB, infective droplet nuclei can remain in the air and can infect someone who breathes them in. TB is not spread by surface contamination.
“We know a lot from the clinical setting,” adds Cardo. “We’ve learned a lot about most of the diseases that are being transmitted. Lab and animal studies may add to that equation, but they aren’t the only way of knowing how they’re transmitted.”
Infection control experts have reviewed the literature and concluded that droplet precautions with surgical masks provide adequate barrier protection for some diseases. For example, plague guidance is based on historical and modern information on transmission patterns of naturally occurring illness.2
“It’s not like [respiratory infections] are such rare events that I think we could have missed something,” says Loretta Litz Fauerbach, MS, CIC, director of infection control at Shands Hospital at the University of Florida in Gainesville and communications team leader for the Association of Professionals in Infection Control and Epidemiology (APIC). “Even with the resurgence of pertussis that’s occurring in the United States, if people are masked, they are not being exposed.
“We have a large history of epidemiology that shows surgical masks protect [against droplet-borne diseases],” she says.
Yet industrial hygienists arrive at different conclusions based on measurements of filtration and face seal properties of masks and respirators and the characteristics of aerosolized particles.
Large droplets expelled from a patient immediately evaporate and become droplet nuclei, notes Steven Lenhart, a retired industrial hygienist from the National Institute for Occupational Safety and Health (NIOSH) who co-authored a literature review on surgical mask and respirator research. The infectivity of the droplet nuclei may vary depending on the microorganism and the immunity of the exposed person.3
Even defining large droplets as 5 micrometers or larger, as they are in CDC’s Guidelines for Isolation Precautions,4 is problematic, Lenhart says. “The room currents in the average room are going to keep that buoyant, and it’s going to penetrate the filter of some surgical masks and get around the seal,” he says.
Lenhart also concludes that outbreak investigations alone shouldn’t be the basis for determining the necessary respiratory choice. Surgical masks provide barrier protection from splashes and splatters, but “surgical masks cannot be considered respirators,” he states.
To health care worker union representatives, CDC and APIC use “canary in the mine” logic: Health care workers aren’t getting sick, therefore, this protection must be adequate.
“It’s medical malpractice, what they’re recommending now,” contends Bill Borwegen, MPH, health and safety director of the Service Employees International Union (SEIU). “There is no such thing as an exclusively droplet agent. . . . They immediately turn into droplet nuclei. There’s no evidence that when they desiccate into droplet nuclei, they become less infectious.”
Confusion on the front lines
From a practical perspective, this issue is infused with confusion and controversy and inadequate science-based guidance for occupational medicine physicians and nurses, Hodgson says. The measurements of filtration properties alone can’t provide answers. “There’s a difference between airborne exposure and delivered dose. Exposure does not equate to delivered agents,” he says.
There are other functional issues, as well. In the case of an avian influenza pandemic, hospitals wouldn’t be able to get enough N95 respirators to protect staff — not to mention the rush to fit-test thousands of additional health care workers.
Yet serious questions remain about how to protect health care workers. For example, it’s unclear for many illnesses how much of the transmission is due to surface contamination vs. inhalation of aerosols or droplets. And not every patient is equally infectious.
“We don’t understand the superspreader phenomenon. We don’t understand host susceptibility issues. And nobody’s researching that. If there’s a research program on those for these emerging diseases, we don’t see it or have input,” Hodgson explains.
Cardo agrees that research gaps remain. “We do believe there is a need for more research, and we are doing more research with the [CDC] Division of TB Elimination and NIOSH,” she says. “Three centers at CDC are working together in terms of looking at the main gaps and seeing how we can do research on that. It is a priority for CDC.”
Meanwhile, it’s tough to tell frontline workers when to wear a surgical mask and when to wear a respirator.
“Operationally, it is very confusing,” says Pam Hirsch, APRN, MS, medical clinical program manager in occupational health at the Veterans Health Administration in Washington, DC. “Many times someone is coming in, and you do not know what they have.
“To say, ‘For this disease, you wear a surgical mask; for this one, you wear an N95’ — where do you go with that? You’re going to grab whatever’s there.”
References
1. 69 Fed Reg 33,034 (June 14, 2004).
2. Kool JL. Risk of person-to-person transmission of pneumonic plague. Clin Infect Dis 2005; 40:1,166-1,172.
3. Lenhart SW, Seitz T, Trout D, et al. Issues affecting respirator selection for workers exposed to infectious aerosols: Emphasis on healthcare settings. Applied Biosafety 2004; 9:20-36.
4. Garner JS, Hospital Infection Control Practices Advisory Committee. Guideline for Isolation Precautions in Hospitals, Part II. 1996. Web site: www.cdc.gov/ncidod/hip/ISOLAT/isopart2.htm.
If terrorists spread pneumonic plague in your community, will surgical masks be sufficient to protect health care workers? That question has renewed a controversy over respiratory protection, this time whether surgical masks are appropriate for some diseases while fit-tested N95 filtering facepiece respirators are required for others.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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