Researchers in the United States have conducted a study demonstrating that personal assessment of whether respirators and face masks fit properly cannot be relied on in efforts to protect against infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
The SARS-CoV-2 virus is the agent responsible for the coronavirus disease 2019 (COVID-19) pandemic that has threatened to overwhelm healthcare services in many countries across the globe.
The pandemic has meant well-fitting respirators and face masks have become crucial pieces of protective equipment among healthcare workers and the general public.
However, supply chain constraints have caused some organizations to replace traditional qualitative and quantitative “fit” testing with self-performed fit checks.
As reported in the journal PLOS ONE, researchers from Cambridge University in San Francisco and Northwestern University in Evanston have shown that a fit check performed according to UK National Health Service (NHS) self-assessment guidelines was unreliable in determining the fit of face coverings.
Most N95 respirators failed to fit participants adequately and fit check responses across all face coverings tested correlated poorly with quantitative fit factor scores.
The importance of well-fitting face masks
The COVID-19 pandemic has highlighted not only the importance of wearing face coverings but also the necessity to ensure a good fit that will reduce the spread of viral particles.
“The importance of fit for N95 respirators has particular implications during the COVID-19 pandemic as these masks are generally reserved for clinicians at a time when hospitals are struggling to cope with the demand for conventional fit testing,” says O’Kelly and colleagues. “Even a small fit issue not detected by the wearer when performing a fit check can greatly decrease the protection offered by the N95 respirator.”
However, constraints on the supply of face masks and fit testing during the pandemic has led many healthcare facilities to replace traditional quantitative and qualitative testing procedures with self-performed tests. Such tests involve the user checking for air leaks and assessing how the mask responds to heavy breathing.
The potential impact of replacing fit testing procedures with self-performed checks is not well understood.
In terms of settings outside of healthcare facilities, there is also a lack of literature exploring the effects of fit on the protection provided by face coverings.
What did the researchers do?
Seven individuals (median age 51 years) self-performed fit checks of N95 and KN95 respirators according to UK NHS guidelines.
Participants then underwent quantitative fit testing while wearing different types of N95 respirators, a KN95 respirator, different surgical masks, and a range of fabric face coverings. Quantitative fit testing involves the continuous measurement of particle concentration both inside and outside of the face-covering while it is being worn.
The researchers evaluated the level of fit and protection provided by each type of mask and how well self-performed checks predicted fit, compared with quantitative testing.
What did they find?
The results showed that a proper fit is essential to ensuring N95 respirators provide high levels of protection.
“Fit is critical to the level of protection offered by respirators,” says O’Kelly ad colleagues.
When N95 respirators were properly fitted, they filtered more than 95% of airborne particles, while poorly fitting respirators provided variable levels of protection that were sometimes similar to the levels provided by surgical and cloth masks.
The N95 respirators provided higher levels of protection than any other category of mask, but 4 out of 7 participants were unable to fit the respirators properly.
Participants were generally unable to reliably determine whether respirators fitted properly, with all of them making at least one incorrect determination of fit after performing a check.
“Our results indicate that the method of fit check for N95 respirators, which is being used in many hospitals, is not reliable and has similar failure rates as previously tested self-assessment protocols,” writes the team.
What about the other types of face-covering?
The study also found that KN95 respirators, surgical masks and fabric masks all achieved similarly low fit factor scores and did not significantly differ in the level of protection they provided.
“For civilian protection, no one type of mask proved superior to another. This is likely due to poor fit in the civilian mask options,” say the researchers.
“Participants were seen to achieve similar protection from a fabric face covering as from a KN95 respirator, whose material should perform similarly to an N95 respirator,” they add.
What do the authors advise?
O’Kelly and colleagues say the findings suggest that traditional quantitative or qualitative fit testing for individuals is highly advisable for people in need of respiratory protection.
“The high proportion of fit test failures, and the associated reduction in the effectiveness, has particular implications for healthcare facilities and other work-environments where fit testing may be abandoned during a pandemic,” they write.
“Having a wide variety of mask models and sizes stockpiled is critical as one mask model cannot be assumed to protect the majority of wearers,” advises the team.
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