In Mexico and South East Asia, face mask wearing to prevent spread of respiratory diseases SARS and swine flu is popular with the public and encouraged but the World Health Organisation and national health agencies seem to be recommending masks for healthcare settings only. Whats the evidence that they work?
The answer is that there isn't much. The text book on my desk (Communicable disease epidemiology and control by Roger Webber) says that masks probably more effective when on the patient than on the general public for preventing flu spreading. And Webber points out that when damp, cloth masks become ineffective. Tight fitting masks that have changeable filters are best. This seems to be the general opinion.
For preventing flu spread handwashing seems a better bet. Flu as well as being airborne is passed though direct contact with mucus from an infected person and this can be left on surfaces.
Here are some relevant papers I have found on the subject:
Research Physical interventions to interrupt or reduce the spread of respiratory viruses: systematic review. Tom Jefferson, Ruth Foxlee, t Chris Del Mar, Liz Dooley, Eliana Ferroni, Bill Hewak, Adi Prabhala, Sree Nair, Alex Rivetti, BMJ, doi: 10.1136/bmj.39393.510347.BE, (Published 27 November 2007)
Non-pharmaceutical public health interventions for pandemic influenza: an evaluation of the evidence base. Julia E Aledort, Nicole Lurie, Jeffrey Wasserman and Samuel A Bozzette, BMC Public Health 2007, 7:208 doi:10.1186/1471-2458-7-208 This article is available from: http://www.biomedcentral.com/1471-2458/7/208
A recent addition to the debate:
MacIntyre CR, Epid MA, Cauchemez S, Dwyer DE, Seale H, Cheung P, et al. Face mask use and control of respiratory virus transmission in households. Emerg Infect Dis. 2009 Feb Available from http://www.cdc.gov/EID/content/15/2/233.htm
This is more theoretical and considers a SARS-like illness:
Modeling control strategies of respiratory pathogens. Pourbohloul, B. Meyers, L. A. Skowronski, D. M. Krajden, M. Patrick, D. M. Brunham, R. C. [email protected]; Division of Mathematical Modeling, University of British Columbia Centre for Disease Control, 655 West 12th Ave, Vancouver, British Columbia, V5Z 4R4, Canada. Emerging Infectious Diseases, 2005, Vol. 11, No. 8, pp. 1249-1256, 36 ref.
And for hygienic measures taken in the 1918-19 outbreak see:
Nonpharmaceutical Interventions Implemented by US Cities During the 1918-1919 Influenza Pandemic. Howard Markel, MD, PhD; Harvey B. Lipman, PhD; J. Alexander Navarro, PhD; Alexandra Sloan, AB; Joseph R. Michalsen, BS; Alexandra Minna Stern, PhD; Martin S. Cetron, MDJAMA. 2007;298:644-654
Studies on Methods of Prevention of Epidemic Influenza. STOKES, J. Jr. HENLE, W. Journal of the American Medical Association, 1942, Sept. 5, Vol. 120, No. 1, pp. 16-20, ref., 2 figs.
The authors review briefly the present methods of preventing epidemic influenza and give a short description of recent experiments of their own. It has already been shown that air-borne influenza A virus can be destroyed by ultra-violet irradiation and that the air-borne transmission of influenza A virus to mice can be prevented by this irradiation or by the use of propylene glycol vapour in the air. The authors used both methods experimentally in a ward divided into seven cubicles in which mice were placed in boxes on bed-frames and allantoic fluid virus was atomized into the air. All the control mice died in 10 days with typical lung lesions. After ultra-violet light only three of 70 died and after propylene glycol none, though some showed lung lesions; the mice were in cubicles containing the atomizer. Similarly, spraying of propylene glycol vapour in a children's ward in a convalescent home stopped the occurrence of respiratory infections over a two months' observation period, while the incidence remained the same as before in an unsprayed adjoining ward. It has been found that formalin-treated influenza A virus from the embryo chick allantoic fluid produced a good antibody response irrespective of whether single or multiple injections were given. This immunization also prevented clinical influenza in a group of children who inhaled, through aviation oxygen masks, atomized allantoic fluid containing virus, though subclinical cases did occur. The authors also mention the effective experimental use of inhalation of immune serum for passive immunization and the possibilities of better results from concentration of antibodies by plasma fractionation. F.O. MacCallum.
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