Discussion

In this large study of employees at a single health network in Australia, approximately 98% of the participants achieved at least one successful respirator fit from the ten different P2/N95 respirators provided. Fit rates were inversely proportional to increasing age, with males generally better suited to the available tested respirators. Clean-shaven individuals were significantly more likely to achieve sufficient respirator seal than non-clean-shaven individuals and an association between fit tester experience and improved fit success was observed.

The results of this study are consistent with those published from previous Australian studies. Ng et al found a 96% fit rate using three-panel flat fold respirators, ^{Reference Ng, Kave, Begg, Bodas, Segal and Williams10} while Milosevic et al compared fit rates of eight FFRs and found a successful fit rate of 93%. ^{Reference Milosevic, Kishore Biswas and Innes9} A study by Wilkinson et al also saw a fit success rate of 83% when testing from a pool of five FFR models. ^{Reference Wilkinson, Pisaniello, Ahmad and Edwards8}

Our findings indicate that the three respirators with the highest fit rates in our cohort were the three-panel flat fold respirators: Industree Trident (86.82%), 3M Aura 9320A+ (84.44%), and 3M Aura 1870+ (64.04%). These findings are echoed by other studies ^{Reference Wilkinson, Pisaniello, Ahmad and Edwards8,Reference Williams, Kave, Begg, Bodas and Ng14–Reference Huh, Jeong and Lim16} with three-panel respirators yielding superior fit rates compared with other respirator types. ^{Reference Ng, Kave, Begg, Bodas, Segal and Williams10} A Taiwanese study by Lin and Chen suggested that three-panel flat fold FFRs allowed for the greatest flexibility to fit various facial contours, particularly when engaging in various physical movements, ^{Reference Lin and Chen15} which is mirrored by a French study that found semi-rigid cup models to be too firm to sufficiently adjust to the intricacies in facial characteristics. ^{Reference Ciotti, Pellissier, Rabaud, Lucet, Abiteboul and Bouvet17} Shin et al also found the three-panel flat fold FFRs had the lowest reduction in respiratory protection when performing aerosol-generating procedures such as chest compressions. ^{Reference Shin, Oh, Lim, Kang, Song and Lee18} However, these findings are not universal. Milosevic et al found that semi-rigid cup models had greater success rates compared to flat fold styles, ^{Reference Milosevic, Kishore Biswas and Innes9} possibly due to differences in fit test protocol, as the study did not follow a predetermined order of respirators during fit testing, leading to a smaller sample size of flat fold models (3.87%) tested and the inclusion of only one three-panel flat fold model (3M Aura 1870+). Additional variables such as ethnicity and facial morphology could also possibly explain this variation in findings.

Both duckbill models were the poorest performing FFRs in the present study, with the BSN 72509-09 (small) producing a fit rate of 17.65%, followed by the Halyard 46827 (small) (22.40%). This is consistent with previously published studies in which duckbills were also found to be more likely to fail compared to their more rigid counterparts. ^{Reference Milosevic, Kishore Biswas and Innes9,Reference Ng, Kave, Begg, Bodas, Segal and Williams10,Reference Ciotti, Pellissier, Rabaud, Lucet, Abiteboul and Bouvet17,Reference Low, Weinberg, Ellard, Hacking and Banyasz19–Reference Allison, Tennant, Xiang, Stephens, Ball and Wilton21}

When evaluating data on US workers to inform respirator design, males and females were found to have significantly different facial anthropometric features which can affect FFR seal. ^{Reference Zhuang, Landsittel, Benson, Roberge and Shaffer22} The present study noted that males were at significantly increased odds (almost 12-fold) to achieve at least one FFR fit when compared to females. This was a similar finding among other QNFT studies, ^{Reference Huh, Jeong and Lim16,Reference McMahon, Wada and Dufresne23–Reference Carvalho, Schumacher, Greig, Wong and El-Boghdadly26} including Ascott et al, who found significantly higher failure rates in females (18.2%) compared to males (9.2%), ^{Reference Ascott, Crowest, Sausmarez, Khan and Chakladar24} and Carvalho et al, who found that a higher proportion of females than males required multiple attempts to achieve a successful fit. ^{Reference Carvalho, Schumacher, Greig, Wong and El-Boghdadly26} Other studies found no difference between sexes, ^{Reference Wilkinson, Pisaniello, Ahmad and Edwards8,Reference Winter, Thomas, Stephens and Davis27–Reference Fakherpour, Jahangiri, Seif, Charkhand, Abbaspour and Floyd29} although some of these utilized sample sizes of <50. ^{Reference Winter, Thomas, Stephens and Davis27,Reference Fakherpour, Jahangiri, Seif, Charkhand, Abbaspour and Floyd29} Milosevic et al was the sole study which found females more readily fitted compared to their male counterparts overall, but this is possibly attributable to increased testing of respirators that were more suited to the females in their cohort. ^{Reference Milosevic, Kishore Biswas and Innes9} Regarding specific models, males were significantly more likely than females to achieve fit in the three-panel flat fold FFRs, whereas females were more likely to achieve a seal in two of the three smaller models available—the Halyard 46827 and BSN 725909-09. It is possible that females are more likely to fit smaller respirators due to their smaller facial anthropometric dimensions. ^{Reference Lin and Chen15,Reference Zhuang, Landsittel, Benson, Roberge and Shaffer22} Despite these results, these two FFRs were still the least successful respirators tested among females in our cohort.

In a 2010 US workforce study of facial anthropometric data, Zhuang et al found that facial characteristics differed significantly among different age groups. ^{Reference Zhuang, Landsittel, Benson, Roberge and Shaffer22} In our study, adjusting for sex and clean-shaven status, younger staff members were significantly more likely to attain a sufficient fit for 5 of the tested FFRs compared to their older counterparts. This finding was consistent with observations made by Milosevic et al, ^{Reference Milosevic, Kishore Biswas and Innes9} potentially suggesting that younger HCWs are more compatible in terms of achieving a tight seal when donning present-day FFRs due to specific facial dimensions. Apart from McMahon et al, which found female HCW <40 years were less likely to achieve fit success, ^{Reference McMahon, Wada and Dufresne23} other QNFT studies did not appear to provide commentary on this phenomenon. Further research is required into whether other factors regarding age affect an individual’s fit, such as increased elastin and collagen composition in younger populations. ^{Reference Reilly and Lozano30}

Unsurprisingly, clean-shaven status significantly affected the ability of individuals to attain a successful FFR fit. This is consistent with previous literature which found facial hair to reduce fit factors by 17-fold. ^{Reference Skretvedt and Loschiavo31} Accordingly, Australian Standards and NIOSH guidelines require all individuals undergoing fit testing to be cleanly shaven, to achieve best possible fit results. ^4,5,12 However, a recent observational audit in Australia found that 45% of male HCWs were not clean-shaven when utilizing N95/P2 respirators. ^{Reference Williams, Begg, Bodas and Ng32} Moreover, 17% of the male employees in our sample for which these data were collected were also classified as not being clean-shaven, suggesting that adherence to this recommendation remains poor.

A decision was made to evaluate fit testers involved in our study, revealing significantly increased odds of achieving a FFR fit if the individual was tested by a “frequent” fit tester as opposed to an “infrequent” fit tester. In a 2010 study, Wilkinson et al described a similar phenomenon attributed to experience, although fit testers were able to select respirators based on previous experience. ^{Reference Wilkinson, Pisaniello, Ahmad and Edwards8} While the predetermined FFR testing order utilised at our health network precluded testers from selecting respirators, the authors of this study suggest that the ability of a frequent tester to more clearly instruct and guide HCWs to don respirators correctly and perform test related tasks, as well as to promptly identify any incidents where this process had not occurred appropriately, may have contributed to this observed difference.

To our knowledge, this is one of the largest Australian QNFT studies comparing various models of P2/N95 respirators. Our data adds weight to the contention that age, sex, and clean-shaven status are important considerations when stocking appropriate FFRs in a healthcare setting, and sheds further light on how experience of the fit tester may affect these fit test results. Over the past 3 years, the COVID-19 pandemic has ushered in a period of great demand for respirators for our frontline workers, with supply chains heavily strained. Combined with the rise of reported adverse effects such as skin irritation and pressure sores leading to potential poor compliance with certain respirators, ^{Reference Tang, Zhang, Chen, Li and Yang33,Reference Shaffer and Janssen34} further research is indicated regarding N95 respirator availability, as well as staff compliance and satisfaction with the fit-tested respirators.

Our study has some limitations. As it was a secondary analysis of existing respirator fit data, it was unable to capture information regarding ethnicity, BMI, and participant facial anthropometric dimensions. Given reduced success rates in Asian females shown in previous literature, ^{Reference Wilkinson, Pisaniello, Ahmad and Edwards8,Reference Huh, Jeong and Lim16,Reference Han and Choi25,Reference Carvalho, Schumacher, Greig, Wong and El-Boghdadly26} data comparing the differences in ethnic makeup and how this affected respirator fit would have been of interest. There was also a lack of data regarding non-binary participants, as this information was not recorded.

Another limitation was due to the nature of the QNFT protocol used. According to the Victorian RPP, ⁵ the predefined order of respirators was dictated by the supply of respirators across Victoria during the peak of the pandemic. It is likely that this, coupled with a recommendation to cease the fit test session after 3 successful fit tests were achieved, may have affected success rates in FFRs lower in the testing order, as they were tested less (yielding a smaller sample size) and potentially on individuals with facial anthropometric dimensions that were more difficult to achieve as suitable seal in. On the other hand, the advantage of this predetermined method over a tester-guided system allowed for less confounding by the fit tester or staff preference and ensured the top three respirators were tested on all participants.

Importantly, applicability of our findings should be noted to be limited to the ten respirators involved in our testing protocol and may not be generalizable to all other circumstances due to differing respirator access and stock. Lastly, despite the QNFT protocol being a more reliable form of fit testing, ⁵ this does not ensure a perfect seal each time. Sufficient respirator seal is heavily reliant on user fit checking with each application of the respirator, ⁵ not just by passing a fit test alone.

In conclusion, 98% of staff achieved a successful fitting of at least one respirator, with three-panel flat fold models (Industree Trident, 3M Aura 9320A+, and 3M Aura 1870+) performing the most consistently. This was significantly affected by younger age, male sex, clean-shaven status, and experience of the fit tester which improved fit rates across majority of the tested respirators. Further research is still required to investigate FFR availability, alongside staff compliance and satisfaction with usage in the clinical setting. Ethnicity is another factor which likely heavily influences respirator fit that has not been extensively explored. Our findings support maintaining existing requirements for workers to remain clean-shaven in high-risk settings where FFRs are required and underscore the importance for respirator manufacturers to test their designs on a variety of people. We hope that the results of this study can better inform governing bodies on a global scale regarding the most appropriate respirators to order and stockpile in order to successfully protect frontline workers in the face of infectious disease.