Table 1.

Characteristics of Studies of Comparison of N95 Respirators and Medical masks in Reducing the Risk of Infection

	Study	Country/Area	Research Type	Participants	Interventions	Outcome	Results
1∗	Loeb et al., 200912	8 hospitals in Ontario	RCT	446	∗Targeted use, fit-tested N95 respirator ∗Targeted use, surgical mask	Laboratory-confirmed respiratory infection, influenza-like illness	•No difference in outcome.
2∗	MacIntyre et al., 2011/20142,3	15 hospitals in Beijing	RCT	1441	∗Continual use, fit-tested N95 respirator ∗Continual use, non–fit-tested N95 respirator ∗Continual use, surgical mask	Laboratory-confirmed respiratory infection, influenza-like illness	•CRI (OR 0.38, 0.17 to 0.86) and laboratory confirmed viral infection (OR 0.19,0.05 to 0.67) significantly lower in N95 group; •Bacterial colonization was significantly lower among HCWs who used N95 respirators (RR 0.34, 0.21 to 0.56); •Dual infections significantly lower in N95 arm
3∗	MacIntyre et al., 20134	19 hospitals in Beijing	RCT	1669	∗Continual use, fit-tested N95 respirator ∗Targeted use, fit-tested N95 respirator ∗Control: continual use, surgical mask	Laboratory-confirmed respiratory infection, influenza-like illness	•Rates of CRI (HR 0.39, 0.21 to 0.71) and bacterial colonization (0.40,0.21 to 0.73) significantly lower in the continuous N95 respirator use arm.
4∗	Loeb et al., 20047	2 hospitals in Ontario	Cohort study	43	∗N95 respirator ∗Surgical mask	Laboratory-confirmed respiratory infection	•Consistently wearing a mask or an N95 while caring for a SARS patient was protective, and consistent use of the N95 mask was more protective. •Risk was reduced by consistent use of a surgical mask, not significantly. •Risk was lower with consistent use of an N95 mask than a surgical mask.
5∗	Seto et al., 20038	5 hospitals in Hong Kong	Case–control studies	13 infected 241 noninfected	∗N95 respirator ∗Surgical mask ∗Paper mask	Laboratory-confirmed respiratory infection	•69 staff used of all four measures were not infected. •All infected staff had omitted at least one measure (P = .0224). •Staff wore masks (P = .0001), gowns (P = .006), and washed their hands (P = .047) get infected fewer vs those who did not, but significant only for masks (P = .011). •Practice of droplets precaution and contact precaution is adequate in significantly reducing the risk of infection after exposures to patients with SARS.
6∗	Zhang et al., 20139	25 hospitals in Beijing	Case–control studies	51 infected 204 noninfected	∗N95 respirator ∗Surgical mask ∗Cloth mask	Laboratory-confirmed respiratory infection	•19.6% (10/51) of cases and 26.0% (53/204) of controls recalled a high-risk procedure on a patient with pandemic (H1N1) 2009. •72.5% (37/51) of cases and 71.6% (146/204) of controls wore medical masks in ≥80% of working time. •5.9% (3/51) of cases and 36.3% (74/204) of controls received pandemic vaccination.
7	MacIntyre et al., 20175	9 hospitals in Beijing	RCT	3591	∗Continuous N95 respirator use ∗Targeted N95 respirator use ∗Medical mask use ∗Control arm.	Laboratory confirmed viral respiratory infection	•Rates of all outcomes were lower in the continuous N95 and/or targeted N95 arms. •laboratory-confirmed bacterial colonization (RR 0.33, 0.21-0.51), laboratory-confirmed viral infections (RR 0.46, 0.23-0.91) droplet-transmitted infections (RR 0.26, 0.16-0.42), laboratory-confirmed influenza was lowest in the continuous N95 arm (RR 0.34, 0.10-1.11), not statistically significant. •Rates of laboratory-confirmed bacterial colonization (RR 0.54, 0.33-0.87) and droplet-transmitted infections (RR 0.43, 0.25-0.72) were lower in the targeted N95 arm.
8	Radonovich et al., 20196	7 hospitals in US	RCT	4051	∗N95 respirators ∗Medical masks	Laboratory-confirmed influenza;	•207 laboratory-confirmed influenza infection events (8.2% of HCP-seasons) in N95 group and 193 (7.2% of HCP-seasons) in mask group (difference, 1.0%, [−0.5% to 2.5%]; P = .18) (OR 1.18, 0.95-1.45). •1,556 acute respiratory illness events in N95 group vs 1,711 in mask group (difference, −21.9 per 1,000 HCP-seasons, −48.2 to 4.4; P = .10). •679 laboratory-detected respiratory infections in N95 group vs 745 in mask group (difference, −8.9 per 1,000 HCP-seasons, −33.3 to 15.4; P = .47). •371 laboratory-confirmed respiratory illness events in N95 group vs 417 in mask group (difference, −8.6 per 1,000 HCP-seasons, −28.2 to 10.9; P = .39). •128 influenza like illness events in N95 group vs 166 in mask group (difference, −11.3 per 1,000 HCP-seasons, −23.8 to 1.3; P = .08). •89.4% of participants reported “always” or “sometimes” wearing their assigned devices in the respirator group vs 90.2% in the mask group.

Abbreviations: CRI (credible interval), HCP (healthcare personnel), HR (hazard rate), OR (odds ratio), RCT (Randomized controlled trial), RR (relative risk), SARS (severe acute respiratory syndrome.

^∗1-6 were included in the meta-analysis: Effectiveness of N95 respirators versus surgical masks in protecting healthcare workers from acute respiratory infection: a systematic review and meta-analysis.¹⁰