A cluster randomized clinical trial comparing fit-tested and non-fit-tested N95 respirators to medical masks to prevent respiratory virus infection in health care workers: RCT of face masks in health workers
Open accessAbstract
BACKGROUND: We compared the efficacy of medical masks, N95 respirators (fit tested and non fit tested), in health care workers (HCWs). METHODS: A cluster randomized clinical trial (RCT) of 1441 HCWs in 15 Beijing hospitals was performed during the 2008/2009 winter. Participants wore masks or respirators during the entire work shift for 4 weeks. Outcomes included clinical respiratory illness (CRI), influenza-like illness (ILI), laboratory-confirmed respiratory virus infection and influenza. A convenience no-mask/respirator group of 481 health workers from nine hospitals was compared. FINDINGS: The rates of CRI (3·9% versus 6·7%), ILI (0·3% versus 0·6%), laboratory-confirmed respiratory virus (1·4% versus 2·6%) and influenza (0·3% versus 1%) infection were consistently lower for the N95 group compared to medical masks. By intention-to-treat analysis, when P values were adjusted for clustering, non-fit-tested N95 respirators were significantly more protective than medical masks against CRI, but no other outcomes were significant. The rates of all outcomes were higher in the convenience no-mask group compared to the intervention arms. There was no significant difference in outcomes between the N95 arms with and without fit testing. Rates of fit test failure were low. In a post hoc analysis adjusted for potential confounders, N95 masks and hospital level were significant, but medical masks, vaccination, handwashing and high-risk procedures were not. INTERPRETATION: Rates of infection in the medical mask group were double that in the N95 group. A benefit of respirators is suggested but would need to be confirmed by a larger trial, as this study may have been underpowered. The finding on fit testing is specific to the type of respirator used in the study and cannot be generalized to other respirators. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry (ANZCTR), ACTRN: ACTRN12609000257268 (http://www.anzctr.org.au).
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Pooling of three trials comparing N95/P2 respirators with medical/surgical masks gave an RR of 0.70 (95% CI 0.45 to 1.10) for clinical respiratory illness.
“Pooling of three trials found an estimate of effect suggesting considerable uncertainty as to whether an N95/P2 respirator provides any benefit compared to medical/surgical masks for the outcome of clinical respiratory illness (RR 0.70, 95% CI 0.45 to 1.10; 7799 participants, very low‐certainty evidence; Analysis 2.1)”
From Physical interventions to interrupt or reduce the spread of respiratory viruses (2023) · cites this paper as MacIntyre 2011
The Results (Table 2; page unavailable) compare N95 respirators with medical masks for clinical respiratory illness and report a lower rate in the N95 group. But this is a single trial reporting an odds ratio of 0.62 (95% CI 0.28–1.35), not a pooling of three trials reporting RR 0.70 (95% CI 0.45–1.10). (LLM, conf=0.86)
Experimental — accuracy not yet measuredN95/P2 respirators may make little or no difference for influenza-like illness compared to medical/surgical masks (RR 0.82, 95% CI 0.66 to 1.03; 8407 participants; low-certainty).
“Based on five trials conducted in four healthcare settings and one household, the estimates of effect for the outcome of ILI (RR 0.82, 95% CI 0.66 to 1.03; 8407 participants, low‐certainty evidence; Analysis 2.1) suggest that N95/P2 respirators may make little or no difference for this outcome”
From Physical interventions to interrupt or reduce the spread of respiratory viruses (2023) · cites this paper as MacIntyre 2011
The Results (Table 2; page not provided) report no statistically significant difference in influenza-like illness between N95 respirators and medical masks in this trial. The source does not report the claimed five-trial pooled estimate, 8,407 participants, or low-certainty rating; its own ILI estimate is an odds ratio of 0.52 (95% CI 0.10–2.57). (LLM, conf=0.88)
Experimental — accuracy not yet measuredThe estimate for clinical respiratory illness suggests considerable uncertainty as to whether N95/P2 respirators provide any benefit compared to medical/surgical masks.
“Pooling of three trials found an estimate of effect suggesting considerable uncertainty as to whether an N95/P2 respirator provides any benefit compared to medical/surgical masks for the outcome of clinical respiratory illness (RR 0.70, 95% CI 0.45 to 1.10; 7799 participants, very low‐certainty evidence; Analysis 2.1)”
From Physical interventions to interrupt or reduce the spread of respiratory viruses (2023) · cites this paper as MacIntyre 2011
The Results (Table 2) report an uncertain clinical respiratory illness estimate for all N95 users versus medical-mask users (OR 0.62, 95% CI 0.28–1.35), and the Discussion says a larger trial is needed for a definitive judgment. This single trial does not report the citing sentence’s pooled three-trial estimate, RR 0.70 (95% CI 0.45–1.10), or its 7,799 participants and very-low-certainty rating. (LLM, conf=0.88)
Experimental — accuracy not yet measuredIn MacIntyre 2011, adverse events were more common with N95 respirators than medical masks, including discomfort (41.9% vs 9.8%), headaches (13.4% vs 3.9%), difficulty breathing (19.4% vs 12.5%), and pressure on the nose (52.2% vs 11.0%).
“MacIntyre 2011 reported that adverse events were more common with N95 respirators; in particular, discomfort was reported in 41.9% of N95 wearers versus 9.8% of medical‐mask wearers (P < 0.01); headaches were more common with N95 (13.4% versus 3.9%; P < 0.01); difficulty breathing was reported more often in the N95 group (19.4% versus 12.5%; P = 0.01); and N95 caused more problems with pressure on”
From Physical interventions to interrupt or reduce the spread of respiratory viruses (2023) · cites this paper as MacIntyre 2011
Six trials assessing the effect of masks were carried out in healthcare workers.
“Of the trials assessing the effect of masks, six were carried out in those at greater exposure (i.e. HCWs) (Jacobs 2009; Loeb 2009; MacIntyre 2011; MacIntyre 2013; MacIntyre 2015; Radonovich 2019).”
From Physical interventions to interrupt or reduce the spread of respiratory viruses (2023) · cites this paper as MacIntyre 2011
Pooling of two studies found an estimate of effect that favoured N95 respirators over medical/surgical masks for clinical respiratory infections (RR 0.47, 95% CI 0.36 to 0.62), but not for influenza-like illness (RR 0.59, 95% CI 0.27 to 1.28).
“Pooling of two studies (MacIntyre 2011; MacIntyre 2013) also found an estimate of effect that favoured N95 respirators to medical/surgical masks for clinical respiratory infections (RR 0.47, 95% CI 0.36 to 0.62), but not for ILI, (RR 0.59, 95% CI 0.27 to 1.28) based on three studies (Loeb 2009: MacIntyre 2011; MacIntyre 2013).”
From Physical interventions to interrupt or reduce the spread of respiratory viruses (2023) · cites this paper as MacIntyre 2011
Smith 2016 pooled three trials and found no difference for laboratory-confirmed respiratory infections (OR 0.89, 95% CI 0.64 to 1.24) or influenza-like illness (OR 0.51, 95% CI 0.19 to 1.41).
“In a meta‐analysis comparing surgical masks with N95 respirators, Smith 2016 pooled three trials and found an estimate of effect suggesting no difference for laboratory‐confirmed respiratory infections (OR 0.89, 95% CI 0.64 to 1.24) or ILI (OR 0.51, 95% CI 0.19 to 1.41) (Loeb 2009; MacIntyre 2011; MacIntyre 2013).”
From Physical interventions to interrupt or reduce the spread of respiratory viruses (2023) · cites this paper as MacIntyre 2011
Offeddu 2017 concluded that masks (either N95/P2 respirators or medical/surgical masks) were effective against clinical respiratory infections (RR 0.59, 95% CI 0.46 to 0.77) and influenza-like illness (RR 0.34, 95% CI 0.14 to 0.82).
“A similar meta‐analysis, Offeddu 2017, based on two trials concluded that masks (either N95/P2 respirators or medical/surgical masks) were effective against clinical respiratory infections (RR 0.59, 95% CI 0.46 to 0.77) and ILI (RR 0.34, 95% CI 0.14 to 0.82) (MacIntyre 2011; MacIntyre 2015).”
From Physical interventions to interrupt or reduce the spread of respiratory viruses (2023) · cites this paper as MacIntyre 2011
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- Authors
- MacIntyre, C. R., Wang, Q., Cauchemez, S., Seale, H., Dwyer, D. E., Yang, P., Shi, W., Gao, Z., Pang, X., Zhang, Y., Wang, X., Duan, W., Rahman, B., & Ferguson, N.
- Affiliations
- UNSW Sydney (AU)
- Beijing Center for Disease Prevention and Control (CN)
- Imperial College London (GB)
- Westmead Hospital (AU)
- ORCID
- Venue
- Influenza and Other Respiratory Viruses
- Publisher
- Wiley
- Published
- 2011-01-27
- Volume
- 5
- Issue
- 3
- Pages
- 170-179
- ISSN
- 1750-2640 (ISSN-L)
- PMC
- PMC4941587
- OpenAlex
- W1557580289
- Cited by
- 257
- References
- 33
- Citations by year
- 2026: 2 · 2025: 4 · 2024: 14 · 2023: 17 · 2022: 29 · 2021: 47 · 2020: 71 · 2019: 6 · 2018: 3 · 2017: 9 · 2016: 9 · 2015: 9 · 2014: 11 · 2013: 13 · 2012: 6
- FWCI
- 9.79
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Influenza and Other Respiratory Viruses (publishedVersion)
- Europe PMC (PubMed Central) (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- Funders
- Medical Research Council
- Topics
- Health Sciences › Medicine › Pulmonary and Respiratory Medicine › Infection Control and Ventilation
- Health Sciences › Medicine › Infectious Diseases › Infection Control in Healthcare
- Health Sciences › Health Professions › Occupational Therapy › Occupational Health and Safety in Workplaces
- Keywords
- N95 respirators, surgical masks, fit testing, respiratory viral infections, influenza, healthcare workers, personal protective equipment, influenza-like illness, 2008-2009 influenza season
- MeSH terms
- Adult, Female, Humans, Male, Masks, Personnel, Hospital, Prospective Studies, Respiratory Protective Devices, Respiratory Tract Infections, Occupational Exposure, Infection Control
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