Surgical masks protect health care workers from influenza infections just as well as N95 respirators, a new randomized controlled trial has determined.

Among 446 hospital nurses randomized to the different protective measures during the 2008-2009 influenza season, the illness developed in 22.9% of those wearing respirators and 23.6% of those wearing masks – an absolute risk difference of less than 1%, Dr. Mark Loeb and his colleagues reported in the Oct. 1 online issue of the JAMA (doi:10.1001/jama.2009.1466).

Dr. Loeb of McMaster University, Hamilton, Ont., and his coauthors cautioned that the results might not apply to situations in which health care workers are exposed to aerosolization procedures, such as bronchoscopy and intubation. However, they wrote, “in routine heath care settings, particularly where the availability of N95 respirators is limited, surgical masks appear to be noninferior to N95 respirators for protecting health care workers against influenza.”

The study was conducted in eight tertiary care hospitals in Ontario from September 2008 to April 2009. In all, 446 nurses were randomized to the two protective devices. The randomization was conducted so that there was an equal mix of groups on each service wing. The groups also were well-balanced with respect to influenza risk factors (medical conditions, immunocompromise, and pregnancy) and influenza vaccination status (30% surgical mask vs. 28% respirator).

Exposure to influenzalike illness in a spouse or roommate was similar between the mask and respirator groups (26% vs. 22%), as was exposure to a child with influenzalike illness (23% vs. 21%).

The primary outcome was a lab-confirmed influenza infection, which included in all the subgroups circulating during that season, including 2009 pandemic A(H1N1).

Overall, influenza occurred in 50 of the surgical mask group participants (23.6%) and in 48 of the respirator group (22.9%), an absolute risk difference of –0.73, indicating that the masks were noninferior to the respirators.

Among those who had the flu, the pandemic strain occurred in 8% of the surgical mask group and 12% of the respirator group. The absolute risk difference of 3.89% also demonstrated that the masks were noninferior to the respirators for pandemic flu.

No adenovirus, respiratory syncytial virus, or parainfluenza 1, 2, or 4 was detected in either group. There were no significant differences in other viruses transmitted by droplet infection, including respiratory syncytial virus B, metapneumovirus, parainfluenza 3, rhinovirus, or coronavirus.

Although significantly more nurses in the mask group developed fever (6% vs. 1%), there were no significant between-group differences in any other symptoms of influenza.

There were 13 visits to physicians by nurses assigned to surgical masks and 13 by those assigned to respirators. Work absenteeism due to illness occurred in 20% of the surgical mask group and 19% of the respirator group.

The results of the study are encouraging but preliminary, Dr. Arjun Srinivasan and Dr. Trish Perl wrote in an accompanying editorial. “Uncovering the truth and identifying the most appropriate way to protect health care professionals will require that other investigators build on this study,” wrote the authors of the Centers for Disease Control and Prevention and Johns Hopkins University, Baltimore, respectively (JAMA 2009 Oct. 1[doi:10.1001/jama.2009.1494v1])

Until those future studies are complete, health care workers should focus on tried-and-true methods of infection control: influenza vaccination, handwashing, and administrative control of sick patients, including sequestering and masking those with suspected respiratory infections when they enter the waiting room.

Health care workers also need to remember that by coming to work sick, they add to the burden of illness for everyone, the authors noted. “[They] commonly work despite having febrile respiratory illness, thereby putting both patients and other health care professionals at risk. The importance of [professional-to-professional] transmission is underappreciated: 14% of [them] likely acquired the 2009 pandemic influenza A(H1N1) from another health care professional. ...Hence, a change in culture is needed; health care professionals must stay home when they are ill and employers must not penalize them when they do so.”

None of the study or editorial authors reported any financial disclosures. The study was supported by the Public Health Agency of Canada.

Copyright (c) 2009 Elsevier Global Medical News. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

一项最新的随机对照试验证实：外科口罩在防止医务工作者流感病毒感染方面与N95级呼吸防护口罩具有同样的良好效果。

 

Mark Loeb博士及其同事在10月1日的《美国医学会杂志》(JAMA)上在线发表的一份报告指出：随机使用不同防护措施的446名医院护士在2008~2009年流感流行季节期间，佩戴N95防护口罩者流感发病率为22.9%，佩戴外科口罩者流感发病率为23.6%，其绝对风险差异小于1%(doi:10.1001/jama.2009.1466)。

 

加拿大安大略省汉密尔顿市麦克马斯特大学的Loeb博士及其合著者警告称，该结果可能并不适用于操作支气管镜和气管插管等存在气溶胶暴露风险的医务工作者。他们写道，但“在普通的医疗机构，特别是N95防护口罩供应有限的医院，外科口罩在防止医务工作者流感感染上似乎并不劣于N95防护口罩。”

 

该研究于2008年9月至2009年4月在加拿大安大略省的8个三级医院展开。共计446名护士被随机分到两个防护用具组。提供不同医疗服务的医务人员在组间进行随机平均分配。该研究小组还对流感风险因素(医疗条件、免疫功能低下和怀孕)和流感疫苗接种状况(外科口罩组30%，呼吸器组28%)做了较好的平衡。

 

两组受试者暴露于有类流感疾病的配偶或室友的发生率类似(26%和22%)，暴露于有类流感疾病的子女的发生率同样相似(23% 比21%)。

 

实验室证实的流感感染作为主要的预后指标，其中包括2009甲型H1N1流感。

 

总体而言，外科口罩组有50名受试者发生流感(23.6%)，N95防护口罩组有48例(22.9%)，其绝对风险差异为–0.73，这表明外科口罩并不劣于N95防护口罩。

 

在流感患者中，外科口罩组大流行流感株感染者为8%，N95防护口罩组为12%，其绝对风险差异为3.89%，同样表明外科口罩在大流行流感的防护上不差于N95防护口罩。

 

两组中均未检查出腺病毒、呼吸道合胞病毒或1、2、4型副流感病毒。其他经飞沫感染传播的病毒亦无显著差异，包括B型呼吸道合胞病毒、偏肺病毒、3型副流感病毒、鼻病毒和冠状病毒。

 

13名受试者在就诊前由护士提供了外科口罩，另有13人佩戴了N95防护口罩。外科口罩组因发病旷工者占20%，N95防护口罩组占19%。

 

美国疾病控制与预防中心(CDC)的Arjun Srinivasan博士和巴尔的摩市约翰霍普金斯大学的Trish Perl 博士在所附的编者按中写道，该研究的结果令人鼓舞，但仅仅是初步工作。“查明真相并找出最适当的方式来保护医务工作者，这需要其他研究人员在该研究基础上继续努力。”(JAMA 2009 Oct. 1[doi:10.1001/jama.2009.1494v1])

 

在进一步研究完成之前，医务工作者应侧重于经检验可靠的感染控制途径，如接种流感疫苗、洗手、加强对病患的管控，包括对进入候诊室的呼吸道感染疑似患者进行隔离并给他们佩戴口罩。

 

作者指出，医务工作者尚需牢记带病工作可增加每个人的患病风险。“尽管有发热症状的呼吸道疾病，(他们)一般会继续工作，从而使患者和其他医务人员处于风险之中。(医务人员间)传播的重要性被低估：罹患2009甲型H1N1流感的医务人员中有14%可能是被其他工作人员传染。因此，医院文化需要做出改变：医务工作者如果得病必须呆在家里，医院不得因此而做出惩罚。”

 

该研究及其作者均无任何财务利益关系。此项研究由加拿大公共卫生局(PHAC)资助。

 

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