September 25, 2009 — Hygiene and physical measures may effectively reduce transmission of respiratory tract viruses including influenza, according to the results of a systematic review reported in the September 23 issue of the BMJ.
"Our 2007 Cochrane review showed that physical interventions (personal hygiene, barriers, and distancing) are highly effective," write Tom Jefferson, MD, from the Acute Respiratory Infections Group, Cochrane Collaboration, in Rome, Italy, and colleagues. "However, the current mainstay of pandemic interventions still seems to be vaccines and antiviral drugs, with no evidence supporting their widespread use, especially against a seemingly mild threat such as the novel H1N1 virus."
The goal of this review was to assess the evidence for efficacy of physical interventions to interrupt or decrease the spread of respiratory tract viruses. The reviewers searched Cochrane Library, Medline, OldMedline, Embase, and CINAHL for studies published in any language or journal regarding any physical intervention to prevent the transmission of respiratory tract viruses. These interventions included isolation, quarantine, social distancing, barriers, personal protection, and hygiene.
Potentially eligible studies included randomized trials, cohort, case-control, crossover, before-and-after, and time series studies. The reviewers first scanned the titles, abstracts, and full-text articles and used a standardized form to determine whether the others were eligible. They then determined potential bias of randomized trials by evaluating generation of the allocation sequence, allocation concealment, blinding, and follow-up. After determination of potential confounders, nonrandomized studies were categorized as having a low, medium, or high risk for bias.
The reviewers identified 58 articles describing 59 studies eligible for inclusion. For all 4 randomized controlled trials and most cluster randomized controlled trials, methodologic quality was poor. The observational studies were of mixed quality.
Physical measures were highly effective in the prevention of transmission of severe acute respiratory syndrome, according to a meta-analysis of 6 case-control studies. The interventions included the following:
- Handwashing more than 10 times daily (odds ratio [OR], 0.45; 95% confidence interval [CI], 0.36 – 0.57; number needed to treat [NNT], 4; 95% CI, 3.65 – 5.52).
- Wearing surgical masks (OR, 0.32; 95% CI, 0.25 – 0.40; NNT, 6; 95% CI, 4.54 – 8.03).
- Wearing N95 masks (OR, 0.09; 95% CI, 0.03 – 0.30; NNT, 3; 95% CI, 2.37 – 4.06).
- Wearing gloves (OR, 0.43; 95% CI, 0.29 – 0.65; NNT, 5; 95% CI, 4.15 – 15.41).
- Wearing gowns (OR, 0.23; 95% CI, 0.14 – 0.37; NNT, 5; 95% CI, 3.37 – 7.12).
- Handwashing, masks, gloves, and gowns combined (OR, 0.09; 95% CI, 0.02 – 0.35; NNT, 3; 95% CI, 2.66 – 4.97).
The combination of handwashing and use of masks, gloves, and gowns also effectively interrupted influenza transmission within households. In younger children and within households, hygienic measures can prevent respiratory tract virus transmission, according to results from the highest-quality cluster randomized trials.
There was limited evidence that the more uncomfortable and expensive N95 masks were more effective than simple surgical masks, but they caused skin irritation. Any additional benefit of adding virucidals or antiseptics to normal handwashing was uncertain, and global measures, such as screening at entry ports, were not properly assessed.
It appeared that social distancing might be effective if used in relationship to the risk for exposure (the higher the risk, the longer the distancing period), but evidence was limited.
"Routine long term implementation of some of the measures to interrupt or reduce the spread of respiratory viruses might be difficult," the review authors write. "However, many simple and low cost interventions reduce the transmission of epidemic respiratory viruses. More resources should be invested into studying which physical interventions are the most effective, flexible, and cost effective means of minimising the impact of acute respiratory tract infections."
Limitations of this study include methodologic limitations of the included studies.
"In situations of high risk of transmission, barrier measures should be implemented such as wearing gloves, gowns, and masks with a filtration apparatus, and isolation of likely cases," the study authors conclude. "Most effort should be concentrated on reducing transmission from young children through regular education at school on hygiene. In addition, society should invest in more comfortable and better designed face masks and barrier apparatus, which would increase compliance with their use."