Testing the Proper Fit Of Respirator Masks During the COVID-19 Pandemic

Occupational exposure to SARS-CoV-2 does not just cause a significant number of cases of occupational disease, it also significantly more frequently results in severe COVID-19 disease in medical staff (1, 2). Aerosol-generating procedures such as intubation and ventilation, large numbers of patient contacts, or specialty-related close patient contact require the use of tightly fitting respirator masks. Filtering respirators (non-reusable FFP2/FFP3 and reusable half masks with P3 filters that meet the EN149:2001 standard) can considerably reduce the risk of SARS-CoV-2 transmission, but only if they fit properly. Since most pathogens of aerosol-borne diseases are tasteless and odorless, wearers cannot tell whether their respirator provides the necessary level of protection unless it is tested for fit. So-called single-use or disposable masks should also be individually fit-tested for each user (figure). Unless this is done, there is a risk that 25% to 75% of staff will remain unprotected despite wearing a respirator mask (3, 4). Fit testing is recommended by the German Social Accident Insurance (DGUV, Deutsche Gesetzliche Unfallversicherung), the Institute for Occupational Safety and Health (IFA), and the Robert Koch Institute (RKI), because “the FFP2/3 mask can give complete protection only if it is worn continuously and is fits properly (i.e., is adjusted to facial features and has a good seal to the skin, as demonstrated by fit testing)” (5).

Figure.

Medical staff carrying out a qualitative fit test during the COVID-19 pandemic. Using a nebulizer, a bitter test agent is sprayed into the hood. If the person being tested does not taste the nebulized test solution during the seven exercises, the fit is deemed acceptable and the test has been passed. This test is intended for use with both disposable and reusable masks.

If proper fit of a mask cannot be achieved, e.g., because the wearer has a beard, the required alternative is a powered air-purifying respirator or blower unit. Variations in facial features result in a relatively high fit failure rate, as is well documented in the literature (3, 4). In the United Kingdom, fit testing for healthcare professionals has been required by law since 2003, and employers can be sued for compensation if infection is proven to derive from occupational exposure. Requirements are similarly strict in the United States, Canada, Australia, and New Zealand, where statutory agencies monitor the implementation of standardized test protocols.

The qualitative fit test is a pass/fail respiratory protection test in which the mask wearer tastes or does not taste an aerosolized test agent (figure). During the test the wearer performs the following seven exercises:

• Normal breathing

• Deep breathing

• Moving the head from side to side

• Moving the head up and down

• Bending at the waist

• Speaking loudly

• Return to normal breathing

The fit test is the responsibility of the employer and is different from the fit check that is to be carried out before the start of every shift. The latter is carried out by the employee every time the mask is put on and shows up any major deficit in fit and adjustment; it is the responsibility of the employee.

Method

From March to June 2020, during the first wave of SARS-CoV-2 infection, at St Thomas’ Hospital in London, UK, and Borstel Medical Clinic, Germany, we carried out qualitative fit testing of various FFP2/3 respirators among medical staff who could potentially come into contact with patients with COVID-19.

Results

London

Among 228 staff (168 women, 60 men), the fit of the FFP3 standard mask failed the test in 72 cases (31.7%; 95% confidence interval: [25.60; 38.04]). It was therefore necessary to repeat the test using a mask of a different model from a different manufacturer or of a different size until suitable respiratory protection was found. The fit test outcome was negative (Fisher’s exact test: P value 0.0006) in 61 of the 168 female staff (36.3% [29.04; 44.07]) and in 11 of the 60 male staff (18.3% [9.52; 30.44]). In 5 members of staff (2.19% [0.72; 5.04]), it was not possible to achieve a proper fit even with a mask of another model.

Borstel

Among 175 staff (149 women, 26 men), a total of 410 fit tests were performed on a variety of FFP2/3 masks, with the aim of identifying as many suitable models as possible and thus avoiding supply shortages. Of the 410 fit tests, 124 (30.24% [25.83; 34.94]) were failed. Among the 149 female staff, 94 of the 341 fit tests were negative (27.57 % [22.89; 32.64]), and among the 26 male staff, 30 of the 69 fit tests were negative (43.48 % [31.58; 55.96]) (Fisher’s exact test: P value: 0.014). In 6 staff (3.4 % [1.27; 7.31]), it was not possible to achieve a proper fit even with a mask of another model.

Discussion

Because of international supply shortages, as early as in March 2020 those of us in London switched to reusable elastomeric half-mask respirators from various manufacturers, so that in course of time all staff members received their half masks after an appropriate fit test. Whilst the London arm of the study followed national occupational health and safety laws, the Borstel arm acted in accordance with DGUV, IFA, and RKI recommendations.

As another useful side effect of fit testing, we found that inferior masks are quickly identified. The most important advantage, however, is that during fit testing the wearer is shown personally how to put on and take off the mask in the correct way to maintain hygiene, acquires confidence in his or her mask, and can at the same time be instructed in the limitations of filtering respiratory protection.

In conclusion, we would like to emphasize that, without fit testing, not all medical staff are protected from aerosol-transmissible pathogens. In our opinion, therefore, the fact that, despite national recommendations, fit testing of respirator masks seems to be the exception, is a problem.

If a case of SARS-CoV-2 infection occurs and there is reason to suspect it was acquired at work, it should be reported immediately as an occupational disease. This is because both symptomatic and asymptomatic COVID-19 can lead to a number of long-term respiratory, cardiac, nephrologic, and neuropsychiatric sequelae, the extent of which cannot be predicted at this time.