Table 1:

Characteristics of studies included in the meta-analysis11–17

Study	Setting	Participants	Outcomes	Interventions	Notes
Randomized controlled trials
Loeb et al., 200911	8 hospitals in Ontario, Canada: emergency departments, acute medical units and pediatric units	446 nurses; individual-level randomization	Laboratory-confirmed respiratory infection, influenza-like illness, workplace absenteeism 5-wk follow-up	Intervention: targeted use, fit-tested N95 respirator Control: targeted use, surgical mask	Noninferiority trial Detection of influenza A and B, respiratory syncytial virus metapneumovirus, parainfluenza virus, rhinovirus–enterovirus, coronavirus and adenovirus
MacIntyre et al., 2011/201412,13	15 hospitals in Beijing: emergency departments and respiratory wards	1441 nurses, doctors and ward clerks; cluster randomization by hospital	Laboratory-confirmed respiratory infection, influenza-like illness 5-wk follow-up	Intervention 1: continual use, fit-tested N95 respirator Intervention 2: continual use, non–fit-tested N95 respirator Control: continual use, surgical mask	Detection of influenza A and B, respiratory syncytial virus metapneumovirus, parainfluenza virus, rhinovirus–enterovirus, coronavirus, adenovirus, Streptococcus pneumoniae, Bordetella pertussis, Chlamydophila pneumoniae, Mycoplasma pneumoniae and Haemophilus influenzae type B
MacIntyre et al., 201314	19 hospitals in Beijing: emergency departments and respiratory wards	1669 nurses, doctors and ward clerks; cluster randomization by ward	Laboratory-confirmed respiratory infection, influenza-like illness 5-wk follow-up	Intervention 1: continual use, fit-tested N95 respirator Intervention 2: targeted use, fit-tested N95 respirator Control: continual use, surgical mask	Detection of influenza A and B, respiratory syncytial virus metapneumovirus, parainfluenza virus, rhinovirus–enterovirus, coronavirus, adenovirus, S. pneumoniae, B. pertussis, C. pneumoniae, M. pneumoniae and H. influenzae type B
Cohort study
Loeb et al., 200415	2 hospitals in Ontario: coronary care units and ICUs with SARS patients	43 nurses	Laboratory-confirmed respiratory infection	Intervention: N95 respirator Control: surgical mask	Retrospective Only 20 nurses reported exposures and consistent use of facial protective equipment Detection of SARS
Case–control studies
Seto et al., 200316	5 hospitals in Hong Kong: emergency departments and medicine units	13 infected (cases) and 241 noninfected (controls) nurses, doctors, health care assistants and domestic staff	Laboratory-confirmed respiratory infection	N95 respirator Surgical mask Paper mask	No cases in N95 respirator or surgical mask groups 143 controls wore either surgical mask or N95 respirator Detection of SARS
Zhang et al., 201317	25 hospitals in Beijing: emergency departments, respiratory wards, ICUs, outpatient departments, technical clinic departments and management	51 infected (cases) and 204 noninfected (controls) doctors, nurses, technicians and other	Laboratory-confirmed respiratory infection	N95 respirator Surgical mask Cloth mask	Cases and controls matched 1:4 by hospital, ward, age and sex 40 cases wore either N95 respirator or surgical mask 159 controls wore either surgical mask or N95 respirator Detection of pandemic H1N1 influenza virus

Note: ICU = intensive care unit, SARS = severe acute respiratory syndrome.