Airborne viruses: The role of fit-tested N95 masks and HEPA filters – Medical News Today

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New research examines the protection offered by fit-tested N95 masks against airborne particles. John Tlumacki/The Boston Globe via Getty Images
  • Healthcare workers rely on N95 respirator masks to keep them safe while treating patients with illnesses caused by airborne viruses, such as COVID-19.
  • New research says the combination of a fit-tested N95 mask and portable HEPA filtration system offers the best protection from viral particles.
  • Researchers believe their study validates a layered approach when it comes to protecting healthcare workers.

Since the start of the COVID-19 pandemic more than 2 years ago, N95 respirator masks have played an important role in the personal protective equipment (PPE) of healthcare workers around the world.

A study in 1998 showed that N95 masks approved by the United States National Institute for Occupational Safety and Health (NIOSH) are capable of filtering out 95% of air particles, though it did not look at viruses. However, more recent studies suggest the fit of a face mask determines how well a mask filters out airborne particles.

Now, a research team from Monash University in Australia says a fit-tested N95 mask combined with a portable HEPA filtration system offers the best protection against viral particles in the air.

The study was recently published in The Journal of Infectious Diseases.

According to lead author Dr. Simon Joosten — respiratory and sleep medicine physician at Monash Health, senior research fellow for Medicine Monash Health at Monash University — this study had two main purposes.

The first was to “quantify the degree of personal contamination with virus aerosol when wearing different types of masks in combination with face shield, gown, and gloves.”

During this study, the research team measured the protection provided by surgical masks, N95 masks, and fit-tested N95 masks.

A disposable surgical mask protects the wearer from large droplets of bodily fluids. It also helps protect patients from the wearer’s respiration.

An N95 mask provides a tighter fit around the face than a surgical mask. It helps protect the wearer from breathing in small aerosol particulates in the air, such as viruses.

Because every person’s face is different, not all sizes and brands of N95 masks fit everyone the same. The U.S. Occupational Safety and Health Administration (OSHA) offers a fit testing procedure where employers help their employees determine which N95 masks provide the most protection.

A fit-tested N95 mask should fit so well it ultimately provides a “seal” between the edges of the mask and the wearer’s face.

In addition to testing the different masks, Dr. Joosten told MNT, the team wanted to determine if the use of a portable HEPA filter enhances the benefit of personal protective equipment to protect the wearer against virus aerosol contamination.

A high-efficiency particulate air (HEPA) filter is capable of removing 99.97% of any air particles with a size of 0.3 microns.

For this study, Dr. Joosten and his team placed a single health worker who was also involved in setting up the experiment, in a sealed clinical room for 40 minutes.

While in the room, the participant 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. For the control test they wore no PPE and no mask.

Researchers exposed the healthcare worker to an aerosolized version of bacteriophage PhiX174, which is a non-hazardous model virus used in experiments because of its small genome size. Researchers then repeated the experiments with a portable HEPA filtration system inside the sealed clinical room.

Following each experiment, researchers took skin swabs from different places on the health workers’ body, including the skin under their mask, inside the nose, and on their forearms, neck, and forehead. The experiment was carried out five times over 5 days.

Upon analyzing the results, Dr. Joosten and his team found a large viral count on both the faces and inside the nose of the healthcare worker when wearing surgical and N95 masks. They found the viral load was considerably lower when wearing fit-tested N95 masks.

Also, the team found the combination of HEPA filtration, fit-tested N95 mask, gloves, gown, and face shield lowered viral counts to near-zero levels.

Dr. Joosten believed the results of this study help validate the importance of using a combination of a fit-tested N95 respirator mask and HEPA filtration for healthcare workers.

“It shows that a fit test passed N95 when combined with a HEPA filter — set to perform 13 air filtration exchanges an hour — can protect against incredibly high amounts of virus aerosol,” he explained.

“[And] it shows that a layered approach to protecting healthcare workers is essential and that HEPA filtration can enhance the protection of healthcare workers in these environments.”

– Dr. Simon Joosten

MNT also spoke with Dr. Fady Youssef, a board certified pulmonologist, internist, and critical care specialist at MemorialCare Long Beach Medical Center in Long Beach, CA about this study. He said the study confirms the importance of fit testing.

“Different brands and different models of N95 masks require their own specific testing — it’s not one size fits all,” Dr. Youssef explained. “The mask is as good as the fit that it has on the face. If you are wearing a mask that doesn’t fit you properly, that’s doing little to nothing to protect you.”

In regards to adding portable HEPA filtration, Dr. Youssef said it makes sense there would be greater synergy and a larger effect when there are two mitigation strategies working together.

“[It] adds further evidence […] to make sure there are multi-tiered mitigation strategies to care for patients that have airborne disease to minimize and hopefully eliminate exposure for healthcare workers that are taking care of them,” he added.

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