Table 2.

 Synopsis of randomised controlled trials evaluating mask and respirator use for influenza

Author/country/year of exposure/(reference)	Study design and participants	Reported results	Limitations
Jacobs/Japan 2008 (4)	Block randomisation to 2 arms and analysed as mask group (17 HCWs wore surgical mask on duty) and no mask group (15 HCWs only wore mask if job‐required e.g. surgical nurse). Outcome measure: Self‐reported cold symptoms scaled to severity.	No difference between two groups; HCWs living with children reported higher severity scores. 84·3% of participants reported full compliance with mask use and non‐use.	Underpowered study; no exposure data; compliance self‐reported; no confirmatory laboratory testing.
Loeb/Canada 2008/09 (5)	Non‐inferiority randomisation of 446 nurses in emergency departments and medical and paediatric units in 8 hospitals to 2 arms and analysed as surgical mask group (212 nurses) and fit‐tested N95 respirator group (210 nurses); mask/respirator worn when caring for patients with febrile respiratory illness during influenza season; assigned respiratory device worn for aerosol‐generating procedures. Outcome measure: Laboratory confirmed influenza by PCR; serology only if no receipt of 2008/09 vaccine.	No difference in influenza infection: 50 (23·6%) of 212 in mask group versus 48 (22·9%) of 210 in N95 group (absolute risk difference, −0·73%; 95% CI −8·8% to 7·3%; P = 0·86). Limited audit found high compliance.	Hard to generalise findings given lack of control arm. Incomplete assessment of compliance and lack of detailed descriptions of exposures.
Cowling/China ‐ Hong Kong 2007 (7)	Cluster randomisation of 198 HHs (index case and HH contacts) to 3 arms and analysed as control (71 HHs and 205 contacts), surgical masks (21 HHs and 61 contacts) or hand hygiene (30 HHs and 84 HH contacts); index cases and contacts asked to wear masks as often as possible at home during the 7‐day follow‐up period (including when with index patient outside of the household). Outcome measure: Culture‐confirmed influenza; self‐reported influenza symptoms.	No difference in laboratory‐confirmed secondary attack ratios in controls 0·06 (95% CI 0·03–0·10), mask 0·07(95% CI 0·02–0·16) and hand hygiene groups 0·06 (95% CI 0·02–0·13), P = 0·99.	Underpowered pilot study; some index cases wore masks in control and hand hygiene arms; difficulty in starting the intervention quickly may have underestimated its true effect. Compliance low: 45% (21%) of index cases (HH contacts) wore mask often/always.
Cowling/China ‐ Hong Kong 2008 (8)	Cluster randomisation of 407 HHs (index case and HH contacts) to 3 arms and analysed as control (91 HHs and 279 contacts), surgical masks and hand hygiene by both index case and contacts (83 HHs and 258 contacts) or hand hygiene (85 HHs and 257 contacts); index cases and contacts asked to wear masks as often as possible at home during the 7‐day follow‐up period (including when with index patient outside of the household). Outcome measure: RT‐PCR positive confirmed influenza; self‐reported influenza symptoms.	No difference in laboratory‐confirmed secondary attack ratios in controls 10% (95% CI 6–14), hand hygiene 5% (95% CI 3–9) and mask plus hand hygiene groups 7% (95% CI 4–11); P = 0·22. Significant reduction in secondary attack ratio if either intervention applied within 36 hours of index case’s onset.	Control and hand hygiene arms ‘contaminated’ as some index cases wore masks; delay in starting intervention quickly may have underestimated its true effect Adherence low: 49% (26%) of index cases (HH contacts) wore mask often/always. Cannot distinguish relative contributions of hand hygiene and mask as they were combined.
MacIntyre/Australia 2006/07 (9)	Cluster randomisation of 145 HHs (index case and HH contacts >16 years) to 3 arms and analysed as control (50 HHs and 100 contacts) or surgical mask (47 HHs and 94 contacts) or P2 respirator (46 HHs and 92 contacts); mask/respirator to be worn at all times when in room with index case. Outcome measure: ILI or laboratory‐ confirmed respiratory virus infection.	No significant differences between ILI rates in controls 16 (16·0%) of 100, in surgical mask group 21 (22·3%) of 94 (RR 1·29, 95%.CI 0·69–2·31, P = 0·46) and in P2 respirator group 14 (15·2%) of 92 (RR 0·95, 95%.CI = 0·49–1·84, P = 1); no difference in respiratory virus isolation rates in controls 3 (3·0%) of 100; in surgical mask group 6 (6·4%) of 94 (RR 2·13, 95% CI 0·55–8·26, P = 0·32); and in P2 respirator group 8 (8·7%) of 92 (RR 2·90, 95% CI 0·79–10·6, P = 0·12). Reduced risk for ILI with adherent mask or respirator use (hazard ratio 0·26, CI 0·09–0·77, P = 0·015).	Underpowered to detect differences between 2 interventions; low level of self‐reported adherence (21% of contacts in the surgical mask and respirator arms wore mask often/always). Interval between index case’s symptom onset and start of intervention not stated; if delayed may have underestimated true effect of intervention.
Aiello/USA, 2006/07 (10)	Cluster parallel randomisation of 1437 students living in university residence halls to 3 arms and analysed as control group (552 students); mask plus hand sanitiser group (367 students); and mask‐only group (378 students); instructed to wear mask as much as possible in residence hall during 6 week intervention period; encouraged to wear outside residence hall also. Outcome measure: self‐reported ILI.	Adjusted analyses found ILI significantly reduced in mask plus hand sanitiser hygiene group compared with controls (during weeks 4–6), ranging from 35% (95% CI 9–53%) to 51% (95% CI 13–73%); reductions in the mask group not significant at P < 0·025.	Hard to generalise given limited age group and specialised setting. Study underpowered to detect small reductions in ILI across arms and the relative contributions of hand hygiene and masks.
Larson/USA 2006/08 (11)	Block randomisation of 617 urban HHs allocated into education (control) group (174 HHs); hand sanitiser group (169 HHs); and hand sanitiser and mask group (166 HHs); household caretaker to wear mask when within 3 feet of person with ILI for 7 days or until symptoms disappeared and to change mask between interactions; ill person encouraged to wear mask when within 3 feet of other HH members. Outcome measure: Self‐reported ILI/URI symptoms and viral culture.	Hand sanitiser group more likely to report no symptomatic HH members (545/946 [57·6%] compared with education (447/904 [49·4%] and hand sanitiser/mask (363/938 [38·7%] groups, P < 0·01; no significant differences in rates of URI, ILI or influenza infection by intervention group in multivariate analyses. Hand sanitiser/mask group had significant reduction in secondary attack rates for URI/ILI/influenza infection (OR 0·82, 95% CI 0·70–0·97) compared with education. No reduction with hand sanitiser alone (OR 1·01, 95% CI 0·85–1·21).	Poor self‐reported compliance with mask use: 22 (50%) of 44 HHs reporting ILI used masks within 48 hours of episode onset; average of 2 (range 0–9) masks/day/ILI episode used. Limited power to detect differences amongst 3 groups; some use of hand sanitiser in control group in response to media reports about methicillin‐resistant Staphylococcus aureus.
MacIntyre/China –Beijing/2008/09 (6)	Cluster, stratified (by size of hospital and level of infection control) randomisation of 1441 HCWs in 15 Beijing hospitals into mask group (492 HCWs/5 hospitals); N95 fit‐tested group (461 HCWs/5 hospitals; and N95 non‐fit‐tested group (488 HCWs/5 hospitals); supplemented with convenience sample of non‐mask‐wearing HCWs from 9 hospitals; participants wore the mask/respirator on every shift for 4 consecutive weeks after being shown when/how to wear it. Outcome measure: Self‐reported CRI, ILI and laboratory‐confirmed viral infection by PCR.	For all outcomes N95 respirators had lower, but not significant, rates compared with masks. Intention‐to‐treat analysis adjusted for clustering of hospitals found only non‐fit‐tested N95s protective against CRI (16/488 [3·3%], OR 0·48, 95% CI 0·24–0·98, P = 0·045) compared with mask group (33/492 [6·7%]) as ref. Multivariate analysis found wearing N95s and hospital level each reduced odds of CRI and laboratory‐confirmed infection.	Monitored and self‐reported compliance good (68–76%) in the 3 arms; however, monitoring by HCWs’ supervisors not optimal method. Limited power to detect differences amongst 3 groups as observed attack rates low. Authors note 46% probability of incorrectly finding one significant difference. Despite stratified randomisation, mask group comprised of only level 3 (most sophisticated) hospitals. Hard to generalise beyond unique study population. Detailed data on potential exposures and information on community levels of influenza not provided.

HCW, healthcare worker; PPE, personal protective equipment; RT‐PCR, reverse transcription‐polymerase chain reaction; ILI, influenza‐like illness; HH, household; URI, upper respiratory infection; CRI, clinical respiratory illness; ref, reference group.