Fit testing

Fit testing
Dr Michelle Ananda-Rajah, Infectious diseases & general medicine physician, VIC
Dr Kate Jardine, Paediatric cardiologist, NSW
Dr Alexander Clarke, Anaesthetist, VIC

Fit testing is an essential component of the safe use of respirators, and standard practice in many industries in Australia and internationally.  Fit testing is not to be confused with the fit check which is the quick self-check performed at the time of donning the respirator. Unfortunately, fit testing has not been adopted widely in the Australian healthcare industry, with the notable exception of South Australia. Kate Cole, occupational hygienist and engineer says:

“I wouldn’t call fit testing ‘best-practice’, because it’s a basic compliance measure and an essential part of a respiratory protection program. I don’t know the specific reasons as to why it is not commonly performed in healthcare, maybe it’s because respiratory protection has not been as heavily relied upon previously, and as such, its use and limitations are not well understood?  P2/N95 respirators only work as intended if they are fitted correctly.“ – Kate Cole

With an ever more important need to protect our healthcare workers against acquisition of COVID-19, we advocate provision of P2, N95 or higher-level respirators to all staff treating COVID-19 patients, coupled with introduction of fit testing as standard practice in all healthcare settings in Australia. This is particularly urgent in Victoria, where there have been >2000 health worker infections.

Why is fit testing important?

Tight-fitting respirator masks, like the disposable P2/N95 masks commonly used in healthcare require a tight seal to provide protection. Without a tight seal, unfiltered air will bypass the filter. An N95 mask can only filter 95% of particles if 100% of the air goes through the filter material.

“A fit-test validates whether a respirator has the potential to provide an adequate fit. Kind of like the reason you try on a pair of shoes before you buy them – not all size 8 shoes will fit the same sized 8 foot (alas!). Respirator styles vary greatly also, and they don’t fit every face shape. I find that generally people want to do the right thing to protect themselves, which is why a key part of fit-testing is the training and instruction that goes along with it.”- Kate Cole.

What are fit-check pass rates like when compared to quantitative fit testing?

Reported initial fit-pass rates for N95/P2-masks vary widely. A study of 638 Asian nursing students (75% women) found that failure rates with fit checks alone compared to quantitative fit testing (on normal and deep breathing) were high, ranging from 31-39% with a 3M mask to 65-66% with a Kimberley Clark variety resembling a duckbill. A study from South Australia involving 6,160 HCWs obtained an overall successful fit in 89% of HCWs using 5 types of N95 respirators {3M1870 regular, Smith & Nephew Proshield N95 (medium, small), Kimberley Clarke Fluid Shield (regular, small)}. Among 4,472 HCWs, 83% achieved a successful fit with the first respirator, 12% needed a second model of respirator and 4.8% required 3 or more models before obtaining a successful fit. Asians were more likely to fail compared to Caucasians at 16% vs. 9.8% respectively. There were no sex differences. The pass rate in this study may be artificially high because an experienced fit tester chose the respirator to test first, based on their experience. It does not reflect the reality of Australian healthcare, where most users are issued a “default” mask from the stockpile, regardless of facial shape.

A recent study from Concord Hospital (Sydney) found that 6.2% of the 371 staff failed the first 4 masks (shown below) and 1.6% failed all five masks. The respirator with the lowest failure rate was the 3M 1860S which many hospitals do not carry. Failure rates for the individual respirators were high but not specified in the publication. A comment in print media from the study author said that the best performing mask failed fit testing 18% of the time and one respirator in widespread use failed 71% of the time. Personal communication from the lead author revealed the following fail rates, noting that not everyone was tested with each respirator: TN01-12 (64%), TN01-11 (71.4%), 3M 1860S (18.2%), 3M 1860 (33.5%) and 3M 1870 Aura (34.6%). The take home message is that although the fail rate individually is high, it can be brought right down with fit-testing because a choice of respirators are provided and individual training and education occurs.

masks

Respirator masks (from left to right): 3M 1860 and 1860S (small size); ProShield TN01–11 (orange “duck bill” medium size) and TN01–12 N95 (small size) masks; 3M Aura 1870+ mask (white).

From Cameron et. al. Australian Health Review 44(4) 542-543, 2020.

Limitations

Passing a fit test does not guarantee that every time a wearer dons a facepiece an adequate fit will be achieved. It identifies that a certain facepiece has the potential to provide an adequate fit, but to maintain this, the wearer must fit the mask correctly and check the fit by performing the quick fit check.

Part of the resistance to introducing fit testing is the cost, logistics and a lack of evidence that conclusively shows that it reduces infection rates in healthcare workers from a study that was underpowered for comparing fit tested vs non fit tested respirators for confirmed influenza. The absence of evidence however, is not evidence of absence. The use of non-fitted N95/P2 respirators along with inadequate room ventilation was implicated in SARS transmissions to HCWs despite adequate PPE.

What do the experts say?

Fit testing is required (not simply recommended) in Australian national guidelines (2019) released pre-pandemic and is required by Australian New Zealand Standard AS/NZS1715 before a user wears a respirator.

            The global manufacturer 3M says, “Fit testing is not  only required by AS/NZS 1715; it’s vital to respiratory safety.”

“Without fit testing, there’s no way of knowing if the respirator is actually able to provide its advertised level of protection for a specific worker.”

Fit testing ensures:

1. Seal, 2. Compatibility and 3. Stability.

Compatibility ensures that the respirator fits with other PPE like goggles. Stability ensures that the seal is maintained with movement.

What types of fit testing are there?
Qualitative fit testing

Qualitative fit testing assesses a wearer’s subjective response to a test agent, usually an aerosolised solution of a sweet or bitter tasting substance. A qualitative fit test is cheap, fast and simple. The wearer has a hood placed over their head and the test agent is sprayed into the hood. The test agent can be saccharin (sweet), Bitrex™ (a bitter tasting substance) or Isoamyl acetate (banana smell). If the mask fits adequately, these particles will not reach the mouth and nose, and the wearer will not be able to taste the bitter substance. If the wearer tastes the substance, the respirator is refitted and the procedure repeated until they can not taste it. Each qualitative fit test method uses seven exercises performed for 1 minute each:

  • Normal breathing.
  • Deep breathing.
  • Moving head side to side.
  • Moving head up and down.
  • Bending over (or jogging if the fit test unit doesn’t permit bending at the waist).
  • Talking.
  • Normal breathing again

Courtesy Dr Celine Barber, Anaesthetist, WA (Clipped prior to exercise phase)

Quantitative fit testing

Quantitative methods provide an objective measure of respirator fit, generating a number referred to as a fit factor. A fit factor is the ratio of the concentration of particles outside the facepiece to the concentration inside the facepiece. A value of >100 is required by NIOSH to indicate sufficient fit (with no leak). The fit-factor cannot differentiate between particle penetration through the respirator (material) and a poor face seal but face seal leakage is by far the greater influence on the fit-factor since the material characteristics are strictly standardised. A quantitative fit test requires the use of specialised particle counting equipment (such as a PortaCount™ Plus machine, TSI Inc.). This test does not require the wearer to don a hood, but instead the mask is pierced with a stylet so that the inside air can be analysed. The process destroys the respirator which is discarded afterwards.

quantative-fit-testing-process

Quantitative fit testing in process from Lam et al. (2016)

The following protocol was described in the Concord Hospital study:

  • Normal breathing
  • Deep breathing
  • Side/side and up/down head movement
  • Talking
  • Bending over
  • Grimacing.

Failure of fit testing was defined as an overall fit-factor ratio of less than 100, or a ratio for an individual exercise of less than 50 using accepted standards.

How often should fit testing be performed?

Fit testing must be done annually, as weight gain or weight loss or facial changes can change the fit of a device.

How long does it take and how much does it cost?

About 15-20 minutes at $50-100 overall.

What happens if fit testing fails?

A range of types and sizes of P2/N95 respirators may need to be fit-tested to find one that achieves a protective seal. If a suitable P2/N95 respirator cannot be found, an alternative – e.g. a powered respirator (with a hood, which does not require fit testing) or elastomeric respirator (which still needs fit testing) – should be considered.

Conclusion

The Australian Standard AS/NZS-1715: 2009 requires a respiratory protection program to be established. Part of that program involves the annual fit-testing of close-fitting respirators. In addition, the Australian Guidelines for the Prevention and Control of Infections in Healthcare (National Health and Medical Research Council, 2019) state that in order for N95/P2-masks to offer maximum desired protection it is essential that the wearer is properly fitted and trained in its safe use i.e. it is “required” not just “recommended”.

Every healthcare worker in South Australia who may be exposed to an airborne virus undergoes fit-testing yearly, as part of the requirement for employment. This is also common practice in many overseas settings, including the United States and Hong Kong . Workers in other industries like mining are routinely provided the minimum standard of annual fit testing for use of respirators. A long-standing culture of neglect in health care has led to a lack of the minimum requirement for fit testing. In many hospitals, work health and safety experts are either absent or play no role in guidance on personal protective equipment. We call for an improved culture of work health and safety in Australian hospitals, and mandated routine fit testing.

Australian healthcare workers need confidence in their respiratory protection for several encounters a day, several days a week, several weeks a year into the future. You wouldn’t buy a pair of shoes without trying them on, so why wouldn’t you want a respirator that can withstand the unpredictable demands of clinical work?

Further reading
Acknowledgements

We thank Kate Cole who is a Certified Occupational Hygienist. A Churchill Fellow with degrees in Science, Engineering and Occupational Hygiene, Kate was named as one of the Top 100 Women of Influence by the Australian Financial Review for her work on controlling silicosis in the construction sector.  She is a passionate advocate for protecting the health of workers, and has supported the COVID-19 pandemic through providing her specialist expertise on respiratory protection and health and safety more broadly.