www.cdc.gov/flu/professionals/infectioncontrol/maskguidance.htm
GUIDELINES & RECOMMENDATIONS
The following interim CDC guidance was developed in response to questions about the role of masks for controlling influenza when suboptimal immunization of the public could increase the frequency of influenza infection.
Human influenza is transmitted from person to person primarily via virus-laden large droplets (particles >5 µm in diameter) that are generated when infected persons cough or sneeze; these large droplets can then be directly deposited onto the mucosal surfaces of the upper respiratory tract of susceptible persons who are near (i.e., within 3 feet) the droplet source. Transmission also may occur through direct and indirect contact with infectious respiratory secretions.
A combination of infection control strategies is recommended to decrease transmission of influenza in health-care settings. These include placing influenza patients in private rooms when possible and having health-care personnel wear masks for close patient contact (i.e., within 3 feet) and gowns and gloves if contact with respiratory secretions is likely (seeHealthcare-Associated Influenza). The use of surgical or procedure masks by infectious patients may help contain their respiratory secretions and limit exposure to others. Likewise, when a patient is not wearing a mask, as when in an isolation room, having health-care personnel mask for close contact with the patient may prevent nose and mouth contact with respiratory droplets. However, no studies have definitively shown that mask use by either infectious patients or health-care personnel prevents influenza transmission. In the United States, disposable surgical and procedure masks have been used widely in health-care settings to prevent exposure to respiratory infections, but they have not been used commonly in community settings (e.g., schools, businesses, public gatherings).
The following recommendations focus on the appropriate use of masks as part of a group of influenza control strategies in health-care settings. Masks are not usually recommended in non-health-care settings; however, this guidance provides other strategies for limiting the spread of influenza in the community.
During periods of increased respiratory infection activity in the community, masks should be offered as part of a respiratory hygiene/cough etiquette strategy to patients who are coughing or have other symptoms of a respiratory infection when they present for health-care services (seeRespiratory Hygiene/Cough Etiquette in Healthcare Settings). Masks should be worn by these patients until
A surgical or procedure mask should be worn by health-care personnel who are in close contact (i.e., within 3 feet) with a patient who has symptoms of a respiratory infection, particularly if fever is present, as recommended forstandard and droplet precautions. These precautions should be maintained until the patient has been determined to be noninfectious or for the duration recommended for the specific infectious agent.
Adults can shed influenza virus 1 daybeforesymptoms appear and up to 5 daysafteronset of illness; thus, the selective use of masks (e.g., in proximity to a known symptomatic person) may not effectively limit transmission in the community. Instead, emphasis should be placed oncough etiquettefor persons with respiratory symptoms whenever they are in the presence of another person, including at home and at school, work, and other public settings. Important components of this strategy include encouraging symptomatic persons to
Persons who are diagnosed with influenza by a physician or who have a febrile respiratory illness during a period of increased influenza activity in the community should remain at home until the fever is resolved and the cough is resolving to avoid exposing other members of the public. If such symptomatic persons cannot stay home during the acute phase of their illness, consideration should be given to having them wear a mask in public places when they may have close contact with other persons. In addition, masks are recommended for use by symptomatic, post-partum women while caring for and nursing their infant (seeGuidance for Prevention and Control of Influenza in the Peri- and Postpartum Settings).
No recommendation can be made at this time for mask use in the community by asymptomatic persons, including those at high risk for complications, to prevent exposure to influenza. If unvaccinated high-risk persons decide to wear masks during periods of increased respiratory illness activity in the community, it is likely they will need to wear them any time they are in a public place and when they are around other household members.
Vaccination is the primary method for preventing influenza in persons at high risk for complications secondary to influenza infection. Because of the influenza vaccine shortage this flu season, the number of high-risk persons receiving vaccine may be less than the number vaccinated in prior years. Administration ofantiviral medications, either for the early treatment of influenza infection or for prophylaxis against infection, is a useful adjunct in the control of influenza in these persons.
インフルエンザ予防におけるマスク着用の意義に関する諸問題
homepage3.nifty.com/sank/jyouhou/BIRDFLU/2006/mask.pdf
インフルエンザ予防におけるマスク着用の意義に関する諸問題
インフルエンザウイルスの感染様式
接触感染：ウイルスを含む飛沫物の付着した物に触れる手を介して感染
飛沫感染：ウイルスを含む飛沫物を吸い込んで感染
飛沫核感染（空気感染）：空中を漂うウイルスを含んだ飛沫核を吸い込んで感染
マスクの目的
・生体に有害な微少粒子（ウイルスを含む飛沫物）が呼吸器内に侵入することを防ぐ。
・上気道内の湿度を高め、侵入したウイルス増殖を抑える。
各マスクにおける粒子の透過性（従来型ガーゼマスク、紙マスクは除外）
不織布製マスク（市販製品の主流）：５ミクロン以上の粒子
Ｎ９５（医療用）：０．３ミクロン以上
ナノフィルター（市販されている）：０．０３ミクロン以上の粒子
インフルエンザウイルス粒子の大きさ A型、B型、C型 直径0.08-0.12 ミクロン
ウイルスを含む気道からの飛沫物質 ５ミクロン以上
ウイルスを含む気道からの飛沫核物質 ０．３ミクロン以上
＊
飛沫核物質：ウイルスを含む飛沫粒子が直径２ミクロン以下になると、空気中で水分が蒸発し乾燥縮小した飛沫核になり、長時間空気中に浮遊し、これが吸入される（空気感染と同義語として用いられることが多い）。
製品
捕捉粒子の大きさ
捕捉可能粒子
不織布製
５ミクロン以上
飛沫物
Ｎ９５
０．３ミクロン以上
飛沫核物
ナノフィルター
０．０３ミクロン以上
ウイルス
着用する際の留意点
正しく着用されているなら、その時間帯は気道内への微小粒子の侵入は防ぐことが出来る。ただしマスク装着面以外の顔面、髪の毛などには、微小粒子は付着していることに注意する。
脱着の際、手指に微少粒子が付着することに注意。手指を十分洗った後、顔面、髪の毛も十分洗って、微小粒子を洗い落とす。
完全に手指、顔面、毛髪の洗いが終了するまで、口、鼻、目に微小粒子が付着しないように注意する。
想定される効果
医療従事者が、ある一定期間、感染防御のために使用するには有効で、その際予防用手袋、ガウン等と併用するのが一般的である。
一般人がインフルエンザ感染予防用として用いることには、各種の論議がある。
以下の留意事項が現実生活で完全に実行することが前提となるが、実際的には不可能と考えられることから、米国では一般市民がインフルエンザ予防のためのマスク着用に関しては否定的である。
・感染者がマスク着用して外出、もしくは他者と相対する場合の効果
感染者の顔や手指、または衣服などにウイルスが付着している可能性がある。
マスクを不用意に着脱することにより、ウイルスは咳やクシャミ、さらに感染者の手指に付着して周辺に拡散する可能性。
