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At present, evidence suggests that the main route of human-to-human transmission of the new Influenza A (H1N1) virus is via respiratory droplets, which are expelled by speaking, sneezing or coughing.
Any person who is in close contact (approximately 1 metre) with someone who has influenza-like symptoms (fever, sneezing, coughing, running nose, chills, muscle ache etc) is at risk of being exposed to potentially infective respiratory droplets.
In health-care settings, studies evaluating measures to reduce the spread of respiratory viruses suggest that the use of masks could reduce the transmission of influenza. Advice on the use of masks in health-care settings is accompanied by information on additional measures that may have impact on its effectiveness, such as training on correct use, regular supplies and proper disposal facilities. In the community, however, the benefits of wearing masks has not been established, especially in open areas, as opposed to enclosed spaces while in close contact with a person with influenza-like symptoms.
Nonetheless, many individuals may wish to wear masks in the home or community setting, particularly if they are in close contact with a person with influenza-like symptoms, for example while providing care to family members. Furthermore, using a mask can enable an individual with influenza-like symptoms to cover their mouth and nose to help contain respiratory droplets, a measure that is part of cough etiquette.
Using a mask incorrectly however, may actually increase the risk of transmission, rather than reduce it. If masks are to be used, this measure should be combined with other general measures to help prevent the human-to-human transmission of influenza, training on the correct use of masks and consideration of cultural and personal values.
 

General advice
It is important to remember that in the community setting the following general measures may be more important than wearing a mask in preventing the spread of influenza.

For individuals who are well:
Maintain distance of at least 1 metre from any individual with influenza-like symptoms, and:• refrain from touching mouth and nose;
• perform hand hygiene frequently, by washing with soap and water or using an alcohol based handrub 3 , especially if touching the mouth and nose and surfaces that are potentially contaminated;
• reduce as much as possible the time spent in close contact with people who might be ill;
• reduce as much as possible the time spent in crowded settings;
• improve airflow in your living space by opening windows as much as possible.

For individuals with influenza-like symptoms:
• stay at home if you feel unwell and follow the local public health recommendations;
• keep distance from well individuals as much as possible (at least 1 metre);
• cover your mouth and nose when coughing or sneezing, with tissues or other suitable
materials, to contain respiratory secretions. Dispose of the material immediately after use
or wash it. Clean hands immediately after contact with respiratory secretions!
• improve airflow in your living space by opening windows as much as possible.
If masks are worn, proper use and disposal is essential to ensure they are potentially effective and to avoid any increase in risk of transmission associated with the incorrect use of masks. The following information on correct use of masks derives from the practices in
health-care settings:
• place mask carefully to cover mouth and nose and tie securely to minimise any gaps between the face and the mask
• while in use, avoid touching the mask− whenever you touch a used mask, for example when removing or washing, clean hands by washing with soap and water or using an alcohol-based handrub
• replace masks with a new clean, dry mask as soon as they become damp/humid
• do not re-use single-use masks
− discard single-use masks after each use and dispose of them immediately upon removing.
Source: WHO