NIOSH says disputed study didn't guide advice on masks

Editor's note: This story was revised after initial posting to specify which arm of the CDC issued the statement described.

Nov 10, 2009 (CIDRAP News) – Officials at the Centers for Disease Control and Prevention (CDC) yesterday rejected a contention from several professional groups that its guidance on respiratory protection for healthcare workers caring for H1N1 patients was influenced by a recent controversial study by Australian researchers.

In an online statement, the National Institute for Occupational Safety and Health (NIOSH), part of the CDC, said a recent Institute of Medicine (IOM) report that the CDC received before updating its recommendations on the topic did not rely on the study by Raina MacIntyre and colleagues of the University of New South Wales.

In its latest guidance, issued in mid October, the CDC reaffirmed that healthcare workers caring for H1N1 patients should wear N-95 respirators rather than surgical masks. N-95s fit tightly to the face and are designed to filter out at least 95% of airborne particles, but health workers say they are uncomfortable and often in short supply.

The Australian authors have said their study showed that N-95 respirators were better than surgical masks in protecting medical workers from influenza and other respiratory viruses, but the significance of the findings remains unclear. The study has not yet been published in a journal.

In an initial report on the study at a conference in September, the authors said they found a statistically significant difference between the N-95s and surgical masks. But at the Infectious Diseases Society of America (IDSA) meeting on Oct 31, they presented a new analysis of their data, prompted by reviewers, which indicated that the N-95s were better but the difference was not significant.

As reported previously, MacIntyre has said her team's results still point to a real difference in levels of protection, but the changes suggested by the reviewers left the study with too little statistical power to demonstrate it.

The IDSA, along with the Society for Healthcare Epidemiology of America (SHEA) and the Association for Professionals in Infection Control and Epidemiology (APIC), have argued that the initial version of the MacIntyre findings influenced the IOM report and, in turn, the CDC guidance. Last week the three groups formally urged the Obama administration to change the guidance.

But NIOSH, in an online statement yesterday, said, "The IOM panel explicitly stated that it did not rely on the MacIntyre study in issuing its recommendations . . ., nor is the IOM report or this study mentioned in the CDC guidance. In presenting the results of the IOM letter report to the sponsors of the review, CDC and OSHA [Occupational Safety and Health Administration], Dr. Ken Shine, the panel chair, made a point of specifically saying that the two recently-conducted randomized trials of respirator use, the MacIntyre and the Loeb studies, were not considered in the committee's decision."

(The Loeb study, published recently in the Journal of the American Medical Association, indicated that surgical masks were not inferior to N-95s in protecting health workers from flu.)

NIOSH said the current CDC recommendation is based "on the unique conditions associated with the current pandemic, including low levels of population immunity to 2009 H1N1 influenza, availability of vaccination programs well after the start of the pandemic, susceptibility to infection of those in the age range of healthcare personnel, increased risk for complications of influenza in some healthcare personnel (eg, pregnant women), and the potential for healthcare personnel to be exposed to 2009 H1N1 influenza patients because of their occupation."

The agency promised to reexamine its recommendations as a number of studies now in the planning stages or under way yield new data on how to protect healthcare workers from flu while on the job.

In their letter to President Obama last week, IDSA, SHEA, and APIC sharply criticized the CDC's guidance and related OSHA requirements. The letter cited the Loeb study and the finding of no significant difference in the reanalysis by MacIntyre and colleagues.

"Due to their disconnect with scientific evidence, these documents [the CDC guidance and OSHA requirements], have engendered significant confusion among healthcare professionals and facilities' administrators; the misallocation of scarce resources to the detriment of both patient and healthcare worker protection; and the creation of skepticism toward federal public and occupational health decision-making," the letter stated.

The groups urged the administration to change the guidance to call for "first-line use of surgical masks for routine H1N1 patient care" and impose a moratorium on enforcement of OSHA's requirement related to the use of N-95s in the H1N1 setting.

"Permitting OSHA to continue to enforce a policy that is not grounded in science will force healthcare facilities to waste time and resources working to comply with a flawed requirement when they instead should be working to enact measures that will have a beneficial impact on patient care and worker safety during this national emergency," the groups stated.

Ashley Mattys, an IDSA spokeswoman, said today that the organizations have not received a response to their letter so far.

See also:

Nov 5 SHEA/IDSA/APIC letter to President Obama

Nov 5 CIDRAP News story "Reanalysis changes findings in respiratory protection study"

Oct 14 CIDRAP News story "CDC keeps N-95 recommendation in H1N1 health worker guidance"

Sep 3 CIDRAP News story "IOM affirms CDC guidance on N95 use in H1N1 setting"

Oct 2 CIDRAP News story "Study suggests masks rival respirators for flu protection"

CDC interim recommendations on infection control for H1N1 in healthcare settings

Newsletter Sign-up

Get CIDRAP news and other free newsletters.

Sign up now»


Unrestricted financial support provided by

Bentson Foundation Unorthodox Philanthropy logo and text 'Leading Underwriter'3M logoGilead 
Grant support for ASP provided by


  Become an underwriter»