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Do physical interventions (isolation, barriers and hygiene) reduce the transmission of respiratory viruses?
Studies were selected which compared physical interventions to prevent transmission of respiratory viruses and controls with no intervention. Outcomes included deaths, cases of viral illness, severity of viral illness and clinical symptoms.
The Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, OLDMEDLINE, CINAHL and archives of the MRC Common Cold Unit were searched for any comparative study to reduce transmission of respiratory viruses: randomised controlled trials (RCTs), cohort studies, case–control studies, and controlled before and after studies (CBAs). References of included studies were checked. No language restrictions were applied. The quality of included studies was assessed based on their design, with a component check for randomised trials, the Newcastle–Ottawa scale for observational studies, and a three-point checklist for CBAs. Sixty studies were included.
The 60 studies described various interventions (including isolation, quarantine, social distancing, barriers, personal protection, hygiene) in very different settings that ranged from schools and daycare centres to military barracks. In most studies, viral incidence in the population was not considered in the analysis. All RCTs had high risk of bias. Risk of bias in observational studies was variable.
High quality cluster-RCTs indicate benefit from hygienic interventions such as handwashing, especially in younger children. Pooled case–control studies suggest that cheap physical barriers are effective in preventing the spread of respiratory viruses (see table 1). The effect of use of virucidals when handwashing, and global measures such as screening at entry ports, remains uncertain. There was limited evidence that N95 respirators and social distancing in high risk areas provide benefit.
Physical interventions may reduce the spread of respiratory viruses.
The Institute of Medicine's quality domains include safety, quality, effectiveness, timeliness, patient-centredness, efficiency and equity.1 It is striking that few data address these domains for a ubiquitous paediatric diagnosis: the respiratory virus. Acute respiratory infection is the leading cause of child mortality globally and results in a large proportion of hospital admissions.
Jefferson and colleagues conducted what is surprisingly the first systematic review of the role of physical barriers (eg, masks, virucidals, handwashing, social distancing, gowning/gloving) in the spread of respiratory viruses in and out of healthcare venues. This review of 60 studies suggested that physical barriers may impede respiratory virus transmission. Handwashing was the best-studied intervention, and appeared efficacious across settings.
Their review of reports published over four decades is striking for (and conclusions limited by) the heterogeneity of settings, study designs and quality of the existing data. Even the few RCTs are plagued by bias. In most studies, information on overall viral incidence and diagnostic strategies utilised was unavailable. It is difficulty to gauge the impact of a strategy without knowing baseline epidemiological and virological data. Additionally, many studies reviewed utilised a bundled approach to barrier interventions, making it difficult to determine the efficacy of single barrier strategies. Finally, most studies to date have had significant confounders.
One conclusion of this review is that rigorous methodologies should be applied to infection control strategies. However, this begs the question of how to design such studies at institutions with disparate diagnostic strategies, patient populations and viral incidences. While randomised trials would be optimal, would we feel comfortable randomising someone away from handwashing, for example?
What, then, is a reasonable strategy? Cohorting patients by symptoms rather than by the results of rapid diagnostic assays, would be a good starting point. There are several studies showing the fallacy of relying on rapid viral assays with suboptimal sensitivity. One hospital in New York had difficulty with appropriate precautions for H1N1 2009 influenza A not being initiated appropriately based solely on laboratory results,2 leading to the need for extensive in-house contact investigations. Given the poor sensitivity of many rapid viral diagnostic assays,3 the low proportion of circulating viruses for which such rapid tests exist, and the overlapping symptomatology of viral respiratory illnesses, isolation precautions should be based upon clinical presentation. At our institution, rigorous emphasis on handwashing with alcohol-based solutions has significantly decreased nosocomial viral transmission in the absence of changes in utilisation of other barrier precautions.
Competing interests None.
Provenance and peer review Commissioned; internally peer reviewed.
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