N-95 masks for influenza?

Absurd. Simply absurd.

I refer primarily to the corner in which CDC has seemingly painted itself with regard to its current recommendation that health care workers wear N-95 respirators when caring for patients with suspect or known influenza. How did this come about?

The first major challenge to the previously universal use of surgical masks for respiratory viral infection was the appearance of avian influenza. It was found that in humans, avian influenza virus tended to attach to receptors deeper in the tracheal-bronchial tree than ordinary seasonal influenza and that influenza viral pneumonia was one of the major morbid events in human avian influenza infection. Furthermore, there was a frightful mortality rate in human infection, approaching 50% in some countries and almost 60% in others. Studies in the late 1990s and early in the present century clearly demonstrated the protective efficacy of N-95 respirators among health care workers caring for patients with avian influenza.

The second big challenge to surgical masks was the SARS pandemic of 2003. Again because of the unusual severity and significant mortality associated with this coronavirus pandemic, N-95 masks were widely recommended for the protection of health care workers. Several published studies supported that recommendation.

Influenza A (H1N1)

Enter influenza A (H1N1) earlier this year. Quite understandably, there was initially great concern about the potential severity of the clinical disease and deaths that this virus might cause; therefore early reliance for health care worker protection was again placed on N-95 respirators. This recommendation seemed to be supported by the early reports on the severity of the disease coming from Mexico.

As the weeks passed by in April, May and June of this year and the virus spread throughout the United States and – indeed – around the world, it became apparent that this pandemic H1N1 virus was really quite benign and quite comparable to seasonal influenza. As the descriptive epidemiology and clinical data were studied further, the age distribution of cases and the risk factors for complications became more apparent and are now reasonably well-defined. In most patients, it is a benign, albeit significant illness, just like seasonal influenza. There does appear to be increased morbidity and slightly increased mortality when compared to seasonal influenza.

Recommendations

Faced with such reassuring information, many organizations resumed recommending droplet precautions, using surgical masks to care for patients with known or suspect influenza, reserving the use of N-95 masks for HCWs carrying out procedures that could possibly generate aerosols. Such organizations included, among others, SHEA, APIC and IDSA. The New York City Health Department also backed away from N-95 masks several months ago. Even CDC’s own Hospital Infection Control Practices Advisory Committee broke ranks and changed its recommendation to droplet precautions using surgical masks. Yet CDC’s official recommendation remained the same: N-95 masks for HCWs.

CDC then sought refuge in the Institute of Medicine (IOM), contracting with them for a thorough review of respiratory protection of health care workers against influenza transmission. The IOM gathered a distinguished group of experts and held several hearings. However, CDC had charged the committee so narrowly, ie, to examine only protective efficacy, that the committee came up with the only conclusion that it could and that was, of course, to recommend N-95 masks for HCW protection. The committee noted, however, in its report that the data were incomplete at best and that more research was necessary. (When did a scientific review committee NOT make that recommendation?)

I’m puzzled by CDC’s decision to use an IOM contract to study this issue. I’m sure the folks at CDC were just as aware of the data as were the IOM’s experts. The IOM committee did hold several hearings and provided the option of public as well as scientific input – and that may help diffuse responsibility and the increasing impatience of the hospital infection control community. Recently, even the American Hospital Association urged CDC to change its recommendation on HCW protection.

CDC has stated that it will issue revised guidance on October 1 and this time they will consider issues of practicality, feasibility, expense, supply and the like, in addition to the scientific issue. Meanwhile, the “second wave” is upon us, well underway in some parts of the country and the reason they are waiting until October 1 escapes me. There is no “win-win” here; they will be criticized no matter what is finally recommended. If they recommend droplet precautions, as was the standard for influenza since CDC began recommending any kind of isolation precautions, criticism will come from service worker unions, some of the public who are trying to impact hospital infection control and probably some politicians and other government agencies (think OSHA) as well. Should they continue to recommend N-95 masks, they risk becoming irrelevant, since U.S. hospitals, almost without exception, will simply not comply. N-95s are too uncomfortable and unpleasant, to say nothing of expensive and unavailable, to wear for an extended period in health care settings.

New research

One of the presentations at the recent ICAAC meeting in San Francisco that generated a lot of media coverage was by Raina MacIntyre, MD, of the University of New South Wales in Sydney, Australia. Her report purported to document the superiority of N-95 masks in preventing influenza transmission in a 24-hospital cooperative study in Beijing, China, carried out during a five-week period during the previous influenza season. A brief article about this presentation may be found on page 28 of this issue of Infectious Disease News, together with a brief and incomplete list of my concerns about this study. This report was said to have been presented to the IOM committee during one of its hearings. MacIntyre was quoted as stating that “it would not be ethical to recommend surgical masks for health care workers,” in response to her findings. To make such a statement requires a passionate belief in the validity of her findings, suggesting at least a possibility of investigator bias and hardly seems justified by what we know at present. There are simply too many unanswered questions, and further evaluation must await examination of published data.

There is no argument, I would hope, that most transmission of influenza is via the droplet route. Similarly, there is no argument about the fact that some transmission of influenza is via the airborne route and thus not amenable to prevention using surgical masks. The only question is how much, and under what circumstances, does airborne transmission occur. Stay tuned!

Addendum:

October 1 has come and gone, and I’m unable as this issue goes to press to find any evidence of a change in CDC’s recommendations for HCW respiratory protection. Meanwhile, the rest of the ID/epidemiology community has clearly moved in a different direction. See IDSA President Anne Gershon’s statement in the lead story in the September 2009 IDSA News.