Physical interventions to interrupt or reduce the spread of respiratory viruses: systematic reviewBMJ 2008; 336 doi: https://doi.org/10.1136/bmj.39393.510347.BE (Published 10 January 2008) Cite this as: BMJ 2008;336:77
All rapid responses
I am interested in working with the CDC, or anyone else, in
conducting research on lowering the resistance of children, teenagers, and
adults in the United States and abroad to wearing facemasks to prevent the
flu or the common cold. I believe this can be done through a campaign
similar to the marketing of "The Pet Rock." Bare with me a moment. My idea
is "Designer Facemasks!" With the proper marketing and advertisement and
endorsements by selected individuals we know that the average TV audience,
over a period of time, can be sold anything!
In this case we are considering "educating" the consumer on a product
that is beneficial to their health. An indication of a an intelligent
person is their willingness to consider an idea that they initially
Competing interests: No competing interests
We note the review of physical interventions to minimise the spread
of respiratory viruses and offer our support to the general hygiene-
related recommendations made. However, we feel the analysis does not
focus sufficiently on the differences in transmission of the various
respiratory viruses. Transmission of some (e.g. influenza) is
predominantly spread by aerosol droplets, of others (e.g. SARS) by close
personal contact, and others (e.g. respiratory syncytial virus; RSV) by
fomites, with varying degrees of overlap between the modes.[2-5]
Therefore, it is no surprise that hand washing amongst young children was
one of the most effective preventative measures; RSV is one of the most
significant respiratory viruses in this age group and fomite transmission
provides the opportunity for prevention of spread through improved
These differences, though, suggest that preventative measures such as
gown and mask wearing need further study to understand their effectiveness
against different respiratory viruses.
1. Jefferson T, Foxlee R, Del Mar C, Dooley L, Ferroni E, Hewak B, et
al. Physical interventions to interrupt or reduce the spread of
respiratory viruses: systematic review. BMJ 2008;336:77-80.
2. Bridges CB, Kuehnert MJ, Hall CB. Transmission of influenza:
implications for control in health care settings. Clin Infect Dis
3. Hall CB. Nosocomial respiratory syncytial virus infections: the
"Cold War" has not ended. Clin Infect Dis 2000;31:590-6.
4. Booth TF, Kournikakis B, Bastien N, Ho J, Kobasa D, Stadnyk L, et
al. Detection of airborne severe acute respiratory syndrome (SARS)
coronavirus and environmental contamination in SARS outbreak units. J
Infect Dis 2005;191:1472-7.
5. Lowen AC, Mubareka S, Steel J, Palese P. Influenza virus
transmission is dependent on relative humidity and temperature. PLoS
DMF has provided consultancy services and received financial support from the pharmaceutical industry in matters relating to influenza and RSV treatment and prevention.
Competing interests: No competing interests
What is one to make of the muted reception to a review paper which says, in essence, that we have methods of fighting all respiratory viruses (not just influenza, coronaviruses, adenoviruses, RSV, SARS and so on)--and that the evidence indicates that these methods are effective, relatively easy to employ, and cheap? Is this not cause for celebration? What is one to conclude? That the only “important” interventions are those pharmaceutical in nature?
The U.S. Centers for Disease Control and Prevention (CDC) claims that “the single best way to prevent seasonal flu is to get vaccinated each year.” Is this possible? Such confidence in influenza vaccines seems misplaced for two reasons. First, if CDC viral surveillance data is correct, then in recent years true influenza viruses have only caused an average of 12% of influenza-like illness (the syndrome the public thinks of as “flu” and, most critically, the syndrome the public is trying to avoid). Since influenza vaccine does not work against non-influenza viruses, how can the agency responsibly claim vaccines are the “best way to prevent seasonal flu”?
Second, the track record for influenza vaccination is not stellar. Over the past years, numerous reviews have shown that the benefits of influenza vaccination have been overstated--most importantly in the elderly population, the very group most needing protection.,
With all the focus on influenza instead of influenza-like illness, we are missing the target, pursuing a health policy that has likely placed a prolonged undue reliance on vaccination and other pharmaceutical measures--and prematurely and (now we know) illegitimately demoting the role of physical barriers like handwashing and masks. Official US recommendations for the prevention and control of influenza are 25,000 words long. Only one sentence of that document mentions non-pharmaceutical interventions, only to brush them off as lacking “inadequate study.” Jefferson et al have reviewed the literature--and the evidence gives reason for optimism. Will policy change?
- Jefferson T et al. Physical interventions to interrupt or reduce the spread of respiratory viruses: systematic review. BMJ. (doi:10.1136/bmj.39393.510347.BE) (published online first: November 27, 2007). http://www.bmj.com/cgi/content/full/bmj.39393.510347.BEv1
- Centers for Disease Control and Prevention. “Preventing Seasonal Flu” http://www.cdc.gov/flu/protect/preventing.htm Retrieved Nov 10, 2007.
- Table 1 in Thompson WW, Shay DK, Weintraub E, et al. Mortality associated with influenza and respiratory syncytial virus in the United States. JAMA 2003;289:179-186. Also online: http://jama.ama-assn.org/cgi/content/full/289/2/179
- Centers for Disease Control and Prevention. “Key facts about influenza and influenza vaccine” (Oct 19, 2007). http://www.cdc.gov/flu/pdf/keyfacts.pdf Retrieved Oct 31, 2007.
- Jefferson T. Influenza vaccination: policy versus evidence. BMJ 2006;333:912-915. Also online: http://www.bmj.com/cgi/content/full/333/7574/912
- Simonsen L, Reichert TA, Viboud C, Blackwelder WC, Taylor RJ, Miller MA. Impact of Influenza Vaccination on Seasonal Mortality in the US Elderly Population. Arch Intern Med 2005;165(3):265-272. Also online: http://archinte.ama-assn.org/cgi/content/full/165/3/265
- CDC. Prevention and Control of Influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP). Morb Mort Weekly Rep (July 13, 2007) 56(RR06);1-54. http://www.cdc.gov/MMWR/preview/mmwrhtml/rr5606a1.htm
I know some of the authors and had a chance to read and comment on the draft manuscript prior to publication.
Competing interests: No competing interests
In 1973, a letter to the editor was published in the New England
Journal of Medicine from Jack Resnick, MD, suggesting ‘…perhaps the
ancient oriental custom of wearing gauze or cloth, surgical-type masks
during a cold has some merit? Perhaps Western society has another lesson
to learn by observing the oriental customs besides acupuncture.’ He
suggested this matter be studied in a rigorous manner (Resnick 1973.)
Since then, there have been many studies on the filtration efficiency
of facemasks, but there has been limited study directed at addressing Dr.
Resnick’s implied question; does wearing a surgical mask protect from
respiratory infection? The practice of wearing a facemask seems to be
commonplace in Asia, and almost absent in the West. Evidence for or
against either approach is lacking. Why has it taken so long to heed Dr.
The review by Jefferson et al provides a much-needed check-up on the
evidence (Jefferson et al 2007.) The United States Centers for Disease
Control and Prevention (CDC) recently issued guidelines for use of
facemasks in preparation for an influenza pandemic, such as that may be
caused by the H5N1 ‘avian flu’ variant (CDC 2007.) In the guidance
document, the use of surgical facemasks by healthcare workers is
recommended when respirators (such as the N-95) are not available. The
authors of the document state the ‘…purpose of this document is to provide
a science based framework to facilitate planning for surgical mask and
respirator use in health care settings during an influenza pandemic,’ and
further state ‘…surgical masks provide benefit against large droplet
exposure and should be worn for all health care activities involving
patients with confirmed or suspected pandemic influenza.’ However, another
CDC recommendation admonishes; ‘Adults can shed influenza virus 1 day
before symptoms appear and up to 5 days after onset 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 on cough etiquette…’[emphasis as in original] (CCID
2005.) Given this information, in a pandemic situation, perhaps
healthcare workers should wear facemasks whenever they are in contact with
patients, and not just in the presence of ‘confirmed or suspected pandemic
influenza.’ The CDC is stockpiling millions of surgical facemasks in
preparation for a possible pandemic (Mitka 2007.) This costs taxpayers
millions of dollars in acquisition, storage, and inventory management
fees. These costs are being incurred based on assumptions that facemasks
prevent influenza infection. However, it is recognized that these types
of masks provide little protection from respiratory particles (Lawrence et
al 2006.) One of the key research questions highlighted in the CDC
guidance document is ‘What are the efficacy and effectiveness of the use
of N95 respirators and surgical masks in preventing influenza
transmission? ’ (CDC 2007.) Indeed, shouldn’t this question be answered
before government recommendations are issued, and tax-payer money spent?
Instead of stockpiling surgical facemasks, which have unproven benefit
against influenza, shouldn’t the government be stockpiling N-95 type
In light of the potential for high mortality in a short timeframe
(high risk), and adequate surrogate evidence of effectiveness of surgical
facemasks, the interim actions and guidance are justified as research is
carried out to address the question of efficacy against influenza.
However, this surrogate evidence is lacking. The evidence for facemasks
in protecting healthcare workers, and for protecting patients from
healthcare workers bears particular scrutiny. Based on several studies
that show high variability in filtration efficacy, the CDC does not
recommend using surgical facemasks to protect against mycobacterium
tuberculosis (CDC 1990, Chen 1992, Weber et al 1993, Fennelley 1997.)
Given that the influenza virus is smaller than m. tuberculosis, it is
reasonable to conclude that the filtration of the virus would be no better
(and likely worse) than m. tuberculosis, so should not be used for this
Using surgical facemasks to protect patients from healthcare workers
(or infected healthcare workers from uninfected healthcare workers) has
also not been demonstrated as effective. Several studies show no benefit
of surgical masks in preventing contamination of the surgical field (Haeri
and Wiley 1980, Tunevall 1991, Tunevall and Jorbeck 1992.) A recent
Cochrane systematic review found only two well-designed studies that
investigated the effectiveness of facemasks in preventing surgical wound
infection in clean surgery (Lipp and Edwards, 2002, 2005.) The larger of
the two studies found no difference, and the smaller study found only a
trend towards reduced incidence of infection when the surgical team used a
mask. These investigations may be considered the ‘highest standard,’ as
compliance and observation of clean technique would be much higher than in
other clinical settings, such as routine inpatient or outpatient care.
And yet, it is just these settings that the Japanese Ministry of Health
Labour and Welfare (MHLW 2007) and the US CDC suggest using surgical
facemasks to limit the spread of respiratory infection. The Japanese MHLW
cites the level of evidence as IIIA; no evidence; strongly recommended.
Although the CDC guideline addresses the use of surgical facemasks
during an influenza pandemic, the use of such masks during usual
healthcare operations is common in other parts of the world today. With
the outbreak of SARS in early 2003, and the recent emergence of the H5N1
`avian flu` as a high-mortality variant capable of human infection, the
concern over respiratory spread of disease has greatly heightened among
the public and among healthcare workers (Lau et al 2007; Lau et al 2007;
Lau et al 2004). However, there is no evidence that these types of masks
are effective in protecting healthcare workers from SARS (Derrick &
Gomersall 2005.) The use of masks by healthcare workers in Japan in
particular, and in Asia in general, has been ascribed in part to the
desire to decrease the risk of respiratory infection from or to patients.
In addition to the Japanese Ministry of Health, Labour, and Welfare
endorsement of the use of facemasks by healthcare workers to minimize the
risk of respiratory infection (MHLW 2007), some Japanese university
hospitals require healthcare workers to wear facemasks during the winter
months (personal communication.) There have been significant research and
development resources applied towards testing and designing facemasks that
have improved filtration efficiency (Li et al 2006, Balazy et al 2006),
but studies reporting clinically oriented research outcomes are lacking.
In Japanese cities and other densely populated areas in Asia,
crowding on public transport can be extreme, with a density of five people
per square meter (UCLA Asia Institute, 2004). In these situations, and
under these conditions, taking measures to limit respiratory droplet
spread to minimize the risk of respiratory infection has strong face
validity, although strong evidence for its effectiveness is lacking.
There have been some published manuscripts describing the possible spread
of infection based on mathematical modeling techniques and the possible
benefit of surgical face masks (Noakes et al 2006; Furuya 2007,) but
patient outcome evidence is sparse.
So let us conduct the studies to determine the clinical efficacy of
surgical facemasks in preventing respiratory infection. Doing so may be
more difficult than one might imagine. In Japan, the widespread use of
facemasks renders evidence for effectiveness almost moot. In the US, fear
of widespread disease with inadequate control measures leaves the
government spending millions of dollars on questionable treatment, for
lack of anything better to offer. A straightforward study design for a
prospective randomized controlled trial is thwarted in two countries. In
Japan, the cultural belief in the effectiveness of the surgical facemask
is strong, and non-compliance with study protocol, even among evidence-
based-medicine-minded healthcare providers, is a serious threat to data
integrity and study validity. In the United States, the cultural
resistance to masking the faces of our healthcare providers is strong,
again posing treatment arm non-compliance as a potentially crippling
threat to the study design. So what can we do? What is needed is a
population with no personal convictions to interfere with pursuing answers
to the facemask question, and those questions with similar social
confounds. Of course, this ‘ideal research population’ for these types of
questions does not exist, nor should it be imposed. This situation re-
emphasizes the importance of animal models of disease, and the need for
continued development of more sophisticated computer modeling. When
society has rendered a decision on effectiveness or acceptability of a
healthcare intervention, studying the evidence for or against its use
becomes extremely difficult. The present commentary is an open invitation
to offer ideas to explore novel ways to address important research
questions in this context.
Bałazy A, Toivola M, Adhikari A, Sivasubramani SK, Reponen T,
Grinshpun SA. Do N95 respirators provide 95% protection level against
airborne viruses, and how adequate are surgical masks? Am J Infect
Control. 2006 Mar;34(2):51-7.
CDC: Guidelines for preventing the transmission of tuberculosis in
healthcare settings, with special focus on HIV related issues. MMWR 39
Centers for Disease Control and Prevention (CDC). Interim guidance on
planning for the use of surgical masks and respirators in health care
settings during an influenza pandemic. Last revised: October 10, 2007.
http://www.pandemicflu.gov/plan/healthcare/maskguidancehc.html Accessed 20
Chen CC, Willeke K: Aerosol penetration through surgical masks. Am J
Infect Control 20:177184, 1992
Coordinating Center for Infectious Diseases (CCID), National Center
for Immunization and Respiratory Diseases (NCIRD). CDC Influenza (flu)
2004-2005 Interim Guidance for the Use of Masks to Control Influenza
Page last updated August 8, 2005, Accessed 22 November 2007.
Derrick JL, Gomersall CD. Protecting healthcare staff from
severe acute respiratory syndrome: filtration capacity of multiple
surgical masks. J Hosp Infect. 2005 Apr;59(4):365-8
Fennelly KP. Personal respiratory protection against mycobacterium
tuberculosis. Clin Chest Med 1997 18(1): 1-17
Furuya H. Risk of transmission of airborne infection during train
commute based on mathematical model. Environ Health Prev Med. 2007 Mar
Ha'eri GB, Wiley AM: The efficacy of standard surgical face masks: An
investigation using "tracer particles." Clin Orthop 148:160162, 1980
Jefferson T, Foxlee R, Del Mar C, Dooley L, Ferroni E, Hewak B,
Prabhala A, Nair S, Rivetti A. Physical interventions to interrupt or
reduce the spread of respiratory viruses: a systematic review. BMJ. 2007
Nov 27 [Epub ahead of print]
Lawrence RB, Duling MG, Calvert CA, Coffey CC. Comparison of
performance of three different types of respiratory protection devices. J
Occup Environ Hyg 2006:3: 46574.
Lau JT, Kim JH, Tsui HY, Griffiths S. Anticipated and current
preventive behaviors in response to an anticipated human-to-human H5N1
epidemic in the Hong Kong Chinese general population. BMC Infect Dis. 2007
Lau JT, Kim JH, Tsui H, Griffiths S. Perceptions related to human
avian influenza and their associations with anticipated psychological and
behavioral responses at the onset of outbreak in the Hong Kong Chinese
general population. Am J Infect Control. 2007 Feb;35(1):38-49.
Lau JT, Yang X, Tsui HY, Pang E. SARS related preventive and risk
behaviours practised by Hong Kong-mainland China cross border travellers
during the outbreak of the SARS epidemic in Hong Kong. J Epidemiol
Community Health. 2004 Dec;58(12):988-96.
Li Y, Wong T, Chung J, Guo YP, Hu JY, Guan YT, Yao L, Song QW, Newton
E. In vivo protective performance of N95 respirator and surgical facemask.
Am J Ind Med. 2006 Dec;49(12):1056-65.
Lipp A and Edwards P. Disposable surgical face masks for preventing
surgical wound infection in clean surgery (Review). Cochrane Database Syst
Rev. 2002 Issue 1:1-12.
Lipp A, Edwards P. Disposable surgical face masks: a systematic
review. Can Oper Room Nurs J. 2005 Sep;23(3):20-1, 24-5, 33-8.
Ministry of Health Labour and Welfare (MHLW). [Anti-flu General
Action] in Japanese http://www.mhlw.go.jp/bunya/kenkou/kekkaku-
kansenshou01/ Accessed 11/26/07.
Mitka M. Face masks, respirators might help during pandemic flu
outbreak JAMA 2007 297(21):2338
Noakes CJ, Beggs CB, Sleigh PA, Kerr KG. Modeling the transmission of
airborne infections in enclosed spaces. Epidemiol Infect 2006; 14:1-10.
Resnick J. Rationale for Chinese gauze masks? N Egnl J Med 1973 Oct
Tunevall TG: Postoperative wound infections and surgical face masks:
A controlled study. World J Surg 15:383388,1991
Tunevall TG, Jorbeck H: Influence of wearing masks on the density of
airborne bacteria in the vicinity of the surgical wound. Eur J Surg
UCLA Asia Institute. Teaching about Japan: population density.
http://www.isop.ucla.edu/eas/japan/geography/density1.htm Last updated:
11/3/04. Accessed 10/5/07.
Weber A, Willeke K, Marchioni R, et al: Aerosol penetration and
leakage characteristics of masks used in the health care industry. Am J
Infect Control 21:167173,1993
Competing interests: No competing interests