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Wash your hands (and more): physical barriers help stop viral infections spreading

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27 October 2009

This updated Cochrane review found that, although the evidence is of limited quality, hygiene and physical barriers can be effective in reducing or preventing the spread of respiratory viruses such as influenza.

Level of evidence:
Level 2 (limited-quality patient-oriented evidence) according to the SORT criteria.

Action
Health professionals should be advocating (and following themselves) the clear public health messages issued by the Department of Health, NHS and Health Protection Agency (HPA) in: “catch it, bin it, kill it” (use of tissues when sneezing and their prompt disposal afterwards, followed by hand washing), and staying away from crowded places and public transport if one has probable swine ‘flu. The HPA recommends that healthcare workers wear a facemask if they come into close contact with a person with symptoms, to reduce their risk of catching the virus from patients. However, its does not recommend that healthy people wear facemasks in their everyday life.

What is the background to this?
Much popular media attention in conjunction with the current swine ‘flu pandemic has focussed on the pros and cons of antivirals (see our blogs for the evidence on antiviral use in adults and children). Respiratory viral infections, including influenza, are transmitted by droplet infection. This systematic review examined the available evidence for physical interventions to interrupt or reduce the spread of these kinds of infections.

What does this study claim?
The systematic review included 58 reports looking at 59 studies. The four randomised controlled trials (RCTs) of individuals and most of the cluster-randomised controlled trials were of poor quality; the observational studies were of mixed quality. The large quantity of data from very disparate studies, which could not be combined in meta-analyses, makes summarising the results difficult.

Most of the case control studies these looked at the effect of measures to reduce the spread of Severe Acute Respiratory Syndrome (SARS) in 2003.  Results from these could be combined and show broadly similar results as in other studies. Compared with no intervention (“doing nothing”), disinfection of living quarters was highly effective in preventing the spread of SARS (odds ratio [OR] 0.30, 95% confidence interval [95%CI] 0.23 to 0.39) and handwashing for a minimum of 11 times a day prevented most cases (OR 0.45, 95%CI 0.36 to 0.57, number needed to treat [NNT] 4), Wearing simple masks was highly effective (OR 0.32, 95%CI 0.25 to 0.40, NNT 6) and wearing N95 masks (respirators with 95% filtration capability) was even more effective (OR 0.09, 95%CI 0.03 to 0.30, NNT 3). Wearing gloves was effective (OR 0.43, 95%CI 0.29 to 0.65, NNT 5) as was wearing gowns (OR 0.23, 95%CI 0.14 to 0.37, NNT 5). Handwashing, gloves, gowns and masks together achieved high effectiveness (OR 0.09, 95%CI 0.02 to 0.35, NNT 3).

The authors conclude that most effect on preventing the spread of respiratory viruses can be expected from hygienic measures in younger children and household members of index cases. Implementing barriers to transmission, isolation, and hygienic measures are effective with the use of relatively cheap interventions to contain epidemics of respiratory viruses, they say.

So what?
The NHS Choices website provides extensive advice about swine ‘flu.  The question and answer section advises people with swine ‘flu against travelling on public transport or visiting crowded places so that they are less likely to spread the illness. It also advises everyone always to cover one’s nose and mouth with a tissue when coughing or sneezing, to dispose of dirty tissues promptly and carefully, to maintain good basic hygiene, for example frequently washing hands, and to clean hard surfaces, such as door handles, often and thoroughly using a normal cleaning product. Alcohol handrubs can be used on visibly clean hands if there is no easy access to soap and water.

NHS Choices says that the Health Protection Agency (HPA) recommends that healthcare workers wear a facemask if they come into close contact with a person with symptoms (within one metre), to reduce their risk of catching the virus from patients. However, the HPA does not recommend that healthy people wear facemasks in their everyday life, as there is no evidence to suggest that this is a useful preventative measure and there are concerns about the risks of not using facemasks correctly. They must be changed regularly as they are not so effective when dampened by a person’s breath. People may infect themselves if they touch the outside of their mask, or may infect others by not throwing away old masks safely.

Study details
Jefferson T, et al. Physical interventions to interrupt or reduce the spread of respiratory viruses: systematic review. BMJ 2009;339:b3675

Sponsorship
NHS research and development programme and National Health and Medical Research Council of Australia.

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