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Physical interventions to interrupt or reduce the spread of respiratory viruses: systematic review

BMJ 2009; 339 doi: (Published 22 September 2009) Cite this as: BMJ 2009;339:b3675
  1. Tom Jefferson, researcher1,
  2. Chris Del Mar, dean2,
  3. Liz Dooley, managing editor, Cochrane Acute Respiratory Infections Group2,
  4. Eliana Ferroni, researcher1,
  5. Lubna A Al-Ansary, Shaikh Abdullah S Bahamdan research chair4,
  6. Ghada A Bawazeer, researcher5,
  7. Mieke L van Driel, professor of general practice 23,
  8. Ruth Foxlee, information specialist6,
  9. Alessandro Rivetti, information specialist7
  1. 1Acute Respiratory Infections Group, Cochrane Collaboration, Rome, Italy
  2. 2Faculty of Health Sciences and Medicine, Bond University, Gold Coast, Australia
  3. 3Department of General Practice and Primary Health Care, Ghent University, Belgium
  4. 4Department of Family and Community Medicine, College of Medicine, King Saud University, Riyadh, Saudi Arabia
  5. 5Department of Clinical Pharmacy and King Khalid University Hospital, King Saud University, Riyadh, Saudi Arabia
  6. 6Department of Health Sciences, University of York, York
  7. 7Cochrane Vaccines Field, Azienda Sanitaria Locale, Alessandria, Italy
  1. Correspondence to: T Jefferson, Cochrane Acute Respiratory Infections Group, 00061 Anguillara Sabazia, Rome, Italy jefferson.tom{at}
  • Accepted 7 September 2009


Objective To review systematically the evidence of effectiveness of physical interventions to interrupt or reduce the spread of respiratory viruses.

Data sources Cochrane Library, Medline, OldMedline, Embase, and CINAHL, without restrictions on language or publication.

Data selection Studies of any intervention to prevent the transmission of respiratory viruses (isolation, quarantine, social distancing, barriers, personal protection, and hygiene). A search of study designs included randomised trials, cohort, case-control, crossover, before and after, and time series studies. After scanning of the titles, abstracts and full text articles as a first filter, a standardised form was used to assess the eligibility of the remainder. Risk of bias of randomised studies was assessed for generation of the allocation sequence, allocation concealment, blinding, and follow-up. Non-randomised studies were assessed for the presence of potential confounders and classified as being at low, medium, or high risk of bias.

Data synthesis 58 papers of 59 studies were included. The quality of the studies was poor for all four randomised controlled trials and most cluster randomised controlled trials; the observational studies were of mixed quality. Meta-analysis of six case-control studies suggested that physical measures are highly effective in preventing the spread of severe acute respiratory syndrome: handwashing more than 10 times daily (odds ratio 0.45, 95% confidence interval 0.36 to 0.57; number needed to treat=4, 95% confidence interval 3.65 to 5.52), wearing masks (0.32, 0.25 to 0.40; NNT=6, 4.54 to 8.03), wearing N95 masks (0.09, 0.03 to 0.30; NNT=3, 2.37 to 4.06), wearing gloves (0.43, 0.29 to 0.65; NNT=5, 4.15 to 15.41), wearing gowns (0.23, 0.14 to 0.37; NNT=5, 3.37 to 7.12), and handwashing, masks, gloves, and gowns combined (0.09, 0.02 to 0.35; NNT=3, 2.66 to 4.97). The combination was also effective in interrupting the spread of influenza within households. The highest quality cluster randomised trials suggested that spread of respiratory viruses can be prevented by hygienic measures in younger children and within households. Evidence that the more uncomfortable and expensive N95 masks were superior to simple surgical masks was limited, but they caused skin irritation. The incremental effect of adding virucidals or antiseptics to normal handwashing to reduce respiratory disease remains uncertain. Global measures, such as screening at entry ports, were not properly evaluated. Evidence was limited for social distancing being effective, especially if related to risk of exposure—that is, the higher the risk the longer the distancing period.

Conclusion Routine long term implementation of some of the measures to interrupt or reduce the spread of respiratory viruses might be difficult. 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.


  • We thank Anne Lyddiatt, Stephanie Kondos, Tom Sandora, Kathryn Glass, Max Bulsara, Rick Shoemaker, Allen Cheng, Bill Hewak, Adi Prabhala, and Sree Nair for their comments on or contributions to present and previous versions of the review; Jørgen Lous for translating a Danish paper and extracting data; Ryuki Kassai for translating a Japanese paper; Taixiang Wu for translating several Chinese papers; Luca De Fiore for supplying information on costs; and Michael Broderick for supplementary study information. LAA-A holds the Shaikh Abdullah S Bahamdan research chair for evidence based health care and knowledge translation at the College of Medicine, King Saud University, Riyadh, Saudi Arabia.

  • Contributors: TOJ, CDM, and LD drafted the protocol. LD, CDM, MVD, and TOJ edited the text of the previous version. RF and AR constructed and ran the search strategy. EF, LA and GAB extracted the data. TOJ, CDM, and MVD checked the data and wrote the final report. All authors contributed to the final report.

  • Funding: NHS research and development programme and National Health and Medical Research Council of Australia. The study sponsor had no role in study design, analysis, conclusions, drafting the report, or the decision to submit the report.

  • Competing interests: None declared.

  • Ethical approval: Not required.

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