Table II.
Overview of Published Studies on Face Mask Protection Against Influenza or Other Respiratory Viruses
| Type of Study | Studied Viruses | Studied Population | Type of Mask Used | Results | Reference |
|---|---|---|---|---|---|
| Prospective case‐control study | Influenza A and B | Hong Kong influenza patients and their household contacts | Surgical masks | • Influenza patients comply better with mask use than their contacts • Between 28 and 45% of influenza patients wearing mask “often or always” • 21% or less of contacts wearing mask “often or always” | 26 |
| Cluster randomized controlled trial | Influenza A and B | Hong Kong influenza patients and their household contacts | Surgical masks | • No significant difference was found between hand hygiene or hand hygiene plus face mask in household contacts of influenza patients | 27 |
| • Hand hygiene and face masks can reduce influenza virus transmission if implemented early after symptom onset in an index patient | |||||
| • Only half of the influenza patients reported regular use of a surgical mask during follow‐up; face mask adherence among household contacts was lower | |||||
| Prospective case‐control study | Influenza A, B, and other acute viral respiratory infections | Adult household contacts of a child with respiratory illness | Surgical masks, P2 masks | • Adherent mask use gives relative reduction of 60–80% in risk of acquiring a respiratory infection | 28 |
| • < 50% of participants wearing the mask “most or all” of the time | |||||
| • No difference in adherence between P2 and surgical mask use | |||||
| Case‐control study | Influenza A, B, and RS‐viruses | Dentists | Not specified | No marked reduction in infection | 29 |
| Observational study | Influenza and other acute viral respiratory infections | Lab respiratory specimens from Hong Kong population | *** | • Possible association between population‐based hygienic measures and reduced incidence • The relative contribution of each of these measures could not be estimated | 30 |
| Retrospective case‐control study | SARS | Hong Kong citizens (probable SARS patients and matched controls) | Not specified | Using a mask frequently in public places was significant protective factor against SARS (OR = 0.27, p< 0.001 in multivariate analysis) | 5 |
| Retrospective case‐control study | SARS | Beijing citizens (probable SARS patients and matched controls) | Not specified | • Wearing masks outside the home was significantly protective against SARS (OR = 0.3 for consistent mask use and OR = 0.4 for sometimes mask use, in multivariate analysis) | 6 |
| • Many persons wearing masks in the community did not use N95 or similar highly efficient masks | |||||
| Retrospective case‐control study | SARS | Health care workers in 5 Hong Kong hospitals | Surgical masks, N95 masks, and paper masks | • The use of masks was significantly associated with noninfection (OR = 0.077, p = 0.0001) | 31 |
| • Surgical and N95 masks were both effective, while paper masks did not significantly reduce the risk of infection | |||||
| Retrospective cohort study | SARS | Nurses in 2 critical care units in Toronto | N95 masks and surgical masks | • Consistently wearing a mask while caring for a SARS patient was significantly protective against SARS (RR = 0.23, p = 0.02) | 32 |
| • The data suggest that N95 masks offer better protection than surgical masks | |||||
| Cohort study | RS‐virus | New York hospital | Not specified | The use of masks does not seem warranted if other infection control procedures such as handwashing are used | 33 |
| Review | SARS | Health care workers | N95 masks and surgical masks | • In most studies, mask use was associated with a reduced risk of infection | 34 |
| • It is still unclear whether N95 masks offered significantly better protection than surgical masks in all clinical situations | |||||