Is N95 Respirator Really Best in H1N1?

December 2009

By Mitchell L. Zoler
Elsevier Global Medical News

PHILADELPHIA -- A revised analysis of data on the ability of N95 respirators to prevent transmission of viral infections, including influenza, to health care workers raised new doubts about the appropriateness of recent guidance from the Centers for Disease Control and Prevention on N95 use for influenza protection.

The new analysis of results from an Australian and Chinese study that compared the efficacy of N95 respirators and surgical masks in blocking transmission of influenza and other viruses to health care workers showed that the relatively expensive and uncomfortable respirators were not significantly better than were surgical masks for preventing transmission, Holly Seale, Ph.D., reported at the annual meeting of the Infectious Diseases Society of America (IDSA).

The report by Dr. Seale was especially notable because it revised high-profile findings reported in September by the senior investigator of the study, Dr. C. Raina MacIntyre, at the annual meeting of the Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).

In her September presentation, Dr. MacIntyre reported that use of N95 respirators led to statistically significant improvement in protection against viral infection, compared with the control, a loose-fitting cloth mask. That analysis failed to show similar benefit from a surgical mask, leading to the inference that N95 respirators had an advantage over surgical masks.

Dr. MacIntyre also presented a limited summary of her group's findings last August during a workshop on personal protective equipment for health care workers organized by the Institute of Medicine. The IOM and ICAAC presentations are believed by several infectious diseases experts to have led to controversial guidance on N95 use by health care workers caring for patients infected with pandemic influenza A(H1N1) that the CDC issued in October (

The guidance said the CDC recommends "use of respiratory protection that is at least as protective as a fit-tested, disposable N95 respirator for health care personnel who are in close contact with patients with suspected or confirmed 2009 H1N1 infection." However, CDC spokesman Thomas W. Skinner noted that the Australian study was not cited by the guidance document.

Now that the most recent report from Dr. MacIntyre's group--the talk by Dr. Seale at the IDSA meeting on Oct. 31--showed no advantage from N95 respirators over surgical masks, several U.S. infectious disease societies and individual physicians intensified their contention that the CDC's N95 guidance has no scientific standing, and is also impractical and expensive and should be withdrawn.

"We hope that the CDC and OSHA [the Occupational Safety and Health Administration, part of the U.S. Department of Labor] will reevaluate their guidance and recommend use of surgical masks for routine care of patients known or suspected to have influenza," said Dr. Mark E. Rupp, professor of infectious diseases at the University of Nebraska Medical Center, Omaha, and president of the Society for Healthcare Epidemiology of America (SHEA). "SHEA continues to believe that N95 respirators should be used in situations where aerosolization of influenza virus is more likely--such as during bronchoscopy or endotracheal intubation."

"SHEA, IDSA, and APIC [the Association for Professionals in Infection Control and Epidemiology] are working to get some movement on this," said Dr. Neil O. Fishman, director of the department of health care epidemiology and infection control at the University of Pennsylvania Health System, Philadelphia, and president-elect of SHEA. "What we'd like to see as an initial step is a suspension of OSHA enforcement [of N95 use during routine care for 2009 H1N1 patients] and then a more careful consideration of the shifting scientific data."

Currently, "we have guidance based on flawed science and that cannot be practically implemented, and OSHA saying that they will enforce the guidance and potentially fine hospitals that don't follow it--so it's a huge mess," Dr. Fishman said in an interview.

Among the practical problems with using N95 respirators as broadly as the CDC recommended are that "it is impossible now to get a supply to meet the guidance," Dr. Fishman said. "If we followed the guidance, we would deplete our stockpile of respirators [at the University of Pennsylvania] in a month, and then we would not have N95 respirators available for the management of tuberculosis patients, where the respirators have a proven benefit."

The Australian study that may have contributed to the guidance involved 24 hospitals and more than 1,900 health care workers in Beijing during December 2008 and January 2009. Fifteen of the hospitals were randomized into three groups. In one group of five hospitals, 461 health care workers consistently and exclusively used fit-tested N95 respirators when seeing patients. In a second group of five hospitals, 488 workers used non-fit tested N95 devices, and in the third group of five hospitals, 492 workers used surgical masks. The researchers also identified a fourth group of nine hospitals that weren't part of the randomization process and were selected because their 481 workers routinely used cloth masks when encountering patients.

The first data analysis, presented to the IOM workshop and at ICAAC, used the nine hospitals with cloth masks as the control group. But as Dr. Seale explained during her report at the IDSA meeting, "we received recommendations during the review of our paper that we not include [this] control arm in the study" because these hospitals weren't part of the randomization process.


Click here to
send us feedback