Discussion
Our review demonstrates significant gender-based variance in standardised anthropometric measurements, with significantly smaller female FD for all measurements. Comparing Asian and black/African groups to Caucasians shows differences in facial geometry such as overall face size and nose measurements. With regard to RPE performance, female and BAME participants have generally low FF scores and/or fit-test PR. However, only a limited number of studies included BAME people in RPE fit-testing. Given the limited number of comparative studies available and heterogeneity in study design, we cannot be conclusive in our evaluation of RPE performance in gender or ethnic groups and their associations with specific anthropometric parameters.
BSI recognises anatomical and structural differences between genders.77 Our review shows that facial measurements included in RFTPs, namely face length, face width and lip width, are smaller for females. This is consistent with a large gender-based anthropometric study.78 In the context of fit-testing; most studies collected data limited to FD included in the LANL and NIOSH bivariate RFTPs. A limited number of studies collected additional facial measurements, such as nose dimensions, and showed that these features are relevant to RPE fit. Hence, the inclusion of these additional dimensions and their correlation to RPE performance would be valuable in future studies.
ISO has reported differences in facial characteristics between Caucasian, Sub-Saharan and European facial types.77 Comparisons between Caucasian and black participants demonstrate that the latter have greater protrusion of lips, greater head depth, and shorter, wider, shallower noses.26 78 Hispanic workers have significantly larger facial features for 14 measurements than Caucasians, with shorter nose protrusion and head length.26 Asian participants have statistically different dimensions as compared with Caucasians for 16 anthropometric values.26 However, only a limited number of studies comparatively evaluate the impact of ethnicity on RPE performance.
Furthermore, disaggregated comparisons are lacking for ethnicities outside predominant American groups (Caucasian, black, Hispanic). Often studies categorise participants as ‘Other’ which includes a diverse group of Central, South and East Asians, even though there are significant anthropometric differences between these groups based on ancestry.79 80 Our review also includes studies using American RFTPs as benchmarks, which show significant proportions of Chinese, Korean and Iranian participants’ facial measurements lie outside the distribution of American RFTPs.66 71 81 82 Additionally, individuals from Asian and black ethnic groups continue to be under-represented in RFTPs. There appears to be an urgent need to use fit-test panels that account for ethnicity-specific differences.
Gender-based anthropometric differences are associated with RPE performance in about half of our studies, the majority of which demonstrate that female participants have significantly lower RPE performance, need a variety of mask models for successful fit and are more likely to fail fit-testing altogether.27–29 50 52 53 56 63 67 68 The heterogeneity in results is likely related to study design, of which RPE availability and the assortment of models on offer are particularly relevant. First, many studies do not make gender-based comparisons of RPE performance for individual mask models, comparing overall fit-testing success between genders instead. This is based on successful fit-testing with at least one respirator, which fails to account for the higher fit-testing failure rates for individual RPE models among females, therefore reducing gender-based differences in RPE performance. Second, provision of one model in limited sizes or RPE designed as ‘one-size-fits-all’ fails to cater to smaller FD. Increasing RPE choice improves user success rates and reduces gender-based fit-testing differences. For example, a study demonstrated that inclusion of two additional models accounts for a 20% improvement in female PR.54 Certainly, several studies included here recommend a variety of RPE should be made available to ensure successful fit-testing.30 56 58 61 62 65 69 71 74 In practice, implementing a comprehensive fit-testing programme is a financial and logistical challenge.59 The variety of RPE in different healthcare environments is variable and procurement dependent. It may not be feasible to test HCWs on all available RPE given the time-consuming nature of fit-testing.
Studies report mixed results for ethnicity-based differences in RPE performance. Small comparative studies have demonstrated lower PR for black and Asian females, but with no effect of ethnicity on FF scores.28 51 61 These studies were likely underpowered to recognise subgroup differences. Studies of Asian populations have consistently yielded higher rates of fit-test failure among Chinese, Koreans, Taiwanese and Iranians, further emphasising the need to consider FD of their population in RPE design.29 52 53 63 66–68 71 72 74 Therefore, RPE currently available does not provide comparable protection across ethnicities, likely disadvantaging those from minority groups. This implies, RPE design may be failing to accommodate for heterogeneity in facial features across diverse user populations due to the limited panels used for international standards in their manufacture.
The 2007 NIOSH updated panel and 2014 ISO standards (ISO 16900-1:2014) aim to reflect greater end user diversity. While efforts to diversify panels have been promulgated, many respirators in current use meet outdated standards from early 2000s (EN 149:2001+A1:2009) which comprise a very limited panel. This is supported by a survey of FFP3 respirators used across acute NHS centres during the COVID-19 pandemic.83 Therefore, designing RPE that fit a wide range of demographics is difficult if RPE is permitted to satisfy standards with limited representation.
In practice, poorly fitted RPE hamper work and user safety.84 85 Widespread concerns around inadequacies in areas of RPE fit-test access, availability and training have been raised.86 87 Unfortunately, the proportion of female and BAME HCWs affected and the need for personalised RPE has not been quantified.85 Studies included in this review were not designed to identify modifications during RPE donning, such as excessive tightening of straps or use of adhesive tape which may allow for successful fit-testing but indicate poor RPE fit. Notably, skin damaged is reported to affect 42%–97% of HCWs and ill-fitting RPE may account for higher rates of adverse reactions among BAME HCWs.83 88–90 Given the lack of data, specific guidance on modification measures are limited from NHS England and NHS Improvement.91 Modifications during RPE donning many affect RPE efficacy and the presence of facial lesions encourage face touching and mask handling, resulting in inadvertent PPE contamination.92–97
Strengths and limitations
This is the first systematic review and meta-analysis of the influence of gender and ethnicity on RPE, to the best of our knowledge. Our search strategy and eligibility criteria were broad and have captured a large number of relevant studies. However, we were limited to English-based databases. We excluded studies in Chinese as we were unable to gain access to the data. This is a significant limitation considering the focus of our review and inclusion of non-English studies may affect results significantly.
Inherent associations exist between gender and FD as well as multicollinearity between FD, although these associations were not always clearly accounted for or reported by studies. Meta-analysis showed significant heterogeneity existed for nine FD. Of these measurements, those with small magnitude of effect (ie, smaller differences in measurements) such as nasal root breadth (MD 0.37 mm), nose length (MD 3.64 mm), nose protrusion (MD 2.03 mm) and lip width (MD 2.82 mm) may be less relevant or irrelevant to gender-based differences in anthropometrics. By extension, they may be less relevant to RPE fit.
There was significant disparity in study design and methodology in gender-based studies. Assessment of study design confirmed anthropometrics were collected by standardised methods. Only one study reported conflicting results, with FD greater for females. Exclusion of this study did not sufficiently improved heterogeneity. BAME people have different FD to Caucasians, and it was suspected that heterogeneity may be result of participant diversity. However, subgroup analysis based on ethnicity was not possible as studies measured varying combinations of FD and ethnicity-based grouping reduced sample size such that meta-analysis would not provide meaningful conclusions. Risk of bias assessment demonstrated most studies failed to meet criteria three, relating to use of prespecified inclusion and exclusion criteria. This may contribute to heterogeneity observed in meta-analysis of anthropometrics and differences in conclusions regarding gender-based differences in RPE performance. Several studies failed to account for their sample size through justification, power calculation or estimate of variance/effect. These risks studies being underpowered to detect differences in RPE performance between gender and/or ethnic groups, and may account for the conflicting results. Limited number of studies included ethnically diverse participants with all relevant anthropometrics. Hence, we cannot be conclusive in our evaluation of RPE performance on gender or ethnic groups and their associations with specific anthropometric parameters.
Future research
Successfully fit-testing HCWs is particularly important in the current climate. Future studies addressing the disparity in RPE fit will require a review of how respirators are designed and tested, including use of a relevant fit-test panel. Studies should aim to include a diverse group of participants inclusive of BAME people to better inform future mask design and fit testing performance. Studies should include the provision of a variety of mask models, brands and sizes, denoting modifications made during the donning process, and the fit-test PR for all mask models tested rather than using an overall success rate. Longitudinal studies on how facial anthropometrics influence fit, but also user comfort and adverse outcomes thereafter would be useful to inform mask designs. The future clearly lies in personalising fit-testing with modern technology. For example, three-dimensional facial model-capture may be used to assess fit in order to reduce time and costs of fit-testing as well as expedite identification of HCWs who need alternative RPE.