Masks or Handwashing?

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. babak.pourbohloul@bccdc.ca; 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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