乌鸦传媒

Ordinary medical masks were as effective as N95 respirators for protecting healthcare personnel against acute respiratory illness, including the flu, in a large randomized trial.

Among some 2,400 healthcare professionals (HCPs) over multiple seasons -- for a total of 4,689 "HCP-seasons" -- 207 laboratory-confirmed influenza events occurred among those assigned to N95 respirators (8.2% of HCP-seasons) versus 193 events in those assigned to regular masks (7.2% of HCP-seasons), reported Lewis J. Radonovich Jr., MD, of the CDC's National Personal Protective Technology Laboratory in Pittsburgh, and colleagues in .

Neither the rate difference of 1 percentage point nor the odds ratio of 1.18 for developing a flu event reached statistical significance in the study, called (Respiratory Protection Effectiveness Clinical Trial).

Medical masks were also no less effective than N95 respirators for preventing secondary study endpoints, including rates of overall acute respiratory illness and influenza-like illness unconfirmed by laboratory analysis.

In the cluster-randomized trial, 137 outpatient clinics at seven U.S. medical centers were randomized to have HCPs wear either regular medical masks or N95 respirators over four flu seasons -- specifically, during the 12-week period each season estimated to be the peak for flu circulation. Pairs of clinics within each center were matched and then assigned to either N95 respirators or masks, which all HCPs would wear on the job. The trial spanned September 2011 to May 2015.

In an , Thomas Talbot, MD, of Vanderbilt University in Nashville, and Hilary Babcock, MD, of Washington University School of Medicine in St. Louis, praised the ResPECT researchers for designing the trial to address many limitations of previous studies comparing N95 respirators and medical masks.

"The pragmatic design of the ResPECT study reflects the conditions that many hospital epidemiologists are accustomed to: HCPs may or may not wear the PPE [personal protective equipment] they are supposed to, may or may not wear it correctly if they do wear it, and may self-report higher levels of adherence to hand hygiene and PPE use than noted by independent observers," they wrote. (Radonovich and colleagues said 89.4% of N95 participants and 90.2% of mask participants reported "always" or "sometimes" wearing the devices.)

Talbot and Babcock said the trial was underpowered for the primary endpoint because of limitations in diagnosing infections, thus potentially missing a true difference. But the conclusion of no difference was still probably correct, the editorialists argued, because the secondary outcomes all pointed in the same direction -- namely, that ordinary masks were just as effective as the bulkier and more expensive N95 respirators in real-world use.

Co-principal investigator Trisha M. Perl, MD, of UT Southwestern Medical Center in Dallas, told 乌鸦传媒 that laboratory-detected respiratory infection was widely considered a more relevant endpoint than laboratory-confirmed influenza.

"From a public health perspective it is more important to have a generic answer than a specific one," she said. "These patients generally present with the same symptoms, and we don't know until they are tested if it is flu, RSV [respiratory syncytial virus], or something else."

Perl added that outpatient medical center settings, such as hospital emergency departments, were chosen as study sites because risk to medical personnel may be greater than in in-patient settings.

"Generally, once a patient is admitted to the hospital with a respiratory tract infection, appropriate precautions are in place," she said.

While earlier lab studies assessing 100% adherence have shown N95 respirators to be more effective than medical masks for reducing exposure to aerosols, studies comparing the two personal protective equipment (PPE) devices in real-world, clinical settings have been inconclusive, Perl said.

During the H1N1 influenza pandemic outbreak of 2009, N95 respirators before the virus's transmission route was fully understood. Around that time, several clinical trials comparing N95 respirators with medical masks were conducted in clinical settings, with mixed results.