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Airborne viruses: The role of fit-tested N95 masks and HEPA filters

Since the start of the COVID-19 pandemic more than 2 years ago, N95 respirators have played an important role in the personal protective equipment (PPE) of healthcare workers around the world.
A 1998 study showed that a National Institute of Occupational Safety and Health (NIOSH)-approved N95 mask was able to filter out 95 percent of airborne particles, although it did not detect the virus.However, recent research has shown that the fit of a mask determines its ability to filter airborne particles.
Now, a research team from Monash University in Australia says fit-tested N95 masks combined with a portable HEPA filtration system offer the best protection against airborne virus particles.
According to lead author Dr Simon Joosten, Monash University Monash Health Medicine Senior Research Fellow and Monash Health Respiratory and Sleep Medicine Physician, the study had two main aims.
The first is to “quantify the extent to which individuals are contaminated with viral aerosols while wearing different types of masks as well as face shields, gowns and gloves”.
For the study, the team measured the protection provided by surgical masks, N95 masks, and fit-tested N95 masks.
Disposable surgical masks protect the wearer from large droplets.It also helps protect the patient from the wearer’s breathing.
N95 masks fit the face better than surgical masks.It helps prevent the wearer from breathing in small airborne aerosol particles, such as viruses.
Because everyone’s face shape is different, not all sizes and brands of N95 masks are suitable for everyone.The U.S. Occupational Safety and Health Administration (OSHA) offers a fit testing program where employers help their employees determine which N95 masks provide the most protection.
A fit-tested N95 mask should fit perfectly, ultimately providing a “seal” between the edge of the mask and the wearer’s face.
Dr. Joosten told MNT that in addition to testing different masks, the team wanted to determine whether the use of portable HEPA filters could enhance the benefits of personal protective equipment to protect the wearer from viral aerosol contamination.
High Efficiency Particulate Air (HEPA) filters remove 99.97% of any airborne particles 0.3 microns in size.
For the study, Dr. Joosten and his team placed a health worker, who also participated in the experimental setup, in a sealed clinical room for 40 minutes.
While in the room, participants either wore PPE, including a pair of gloves, a gown, a face shield, and one of three types of masks—surgical, N95, or fit-tested N95.In the control tests, they did not wear PPE, nor did they wear masks.
The researchers exposed healthcare workers to a nebulized version of the phage PhiX174, a harmless model virus used in the experiments because of its small genome.The researchers then repeated the experiment using a portable HEPA filtration system in a sealed clinical room.
After each experiment, the researchers took skin swabs from various locations on the health worker’s body, including the skin under the mask, the inside of the nose, and the skin on the forearm, neck and forehead.The experiment was performed 5 times over 5 days.
After analyzing the results, Dr. Joosten and his team found that when healthcare workers wore surgical masks and N95 masks, they had large amounts of the virus inside their faces and noses.They found that viral loads were much lower when fit-tested N95 masks were worn.
Additionally, the team found that the combination of HEPA filtration, fit-tested N95 masks, gloves, gowns and face shields reduced virus counts to near-zero levels.
Dr. Joosten believes that the results of this study help validate the importance of combining fit-tested N95 respirators with HEPA filtration for healthcare workers.
“It shows that when combined with a HEPA filter (13 air filter exchanges per hour), passing the N95′s fit test can protect against large amounts of viral aerosols,” he explained.
“[And] it shows that a layered approach to protecting healthcare workers is critical and that HEPA filtering can enhance protection for healthcare workers in these settings.”
MNT also spoke with Dr. Fady Youssef, a certified pulmonologist, physician and critical care specialist at MemorialCare Long Beach Medical Center in Long Beach, California, about the study.He said the study confirmed the importance of fitness testing.
“Different brands and models of N95 masks require their own specific testing — it’s not one-size-fits-all,” explained Dr. Youssef.”The mask is as good as it fits on the face. If you’re wearing a mask that doesn’t fit you, it’s doing little to protect you.”
Regarding the addition of portable HEPA filtering, Dr. Youssef said that when the two mitigation strategies work together, it makes sense that there would be greater synergy and greater effect.
“[It] adds further evidence […] to ensure that there are multiple layers of mitigation strategies to care for patients with airborne diseases to minimize and hopefully eliminate exposure to healthcare workers who are caring for them,” he added.
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Post time: May-21-2022