Facemasks and good hand hygiene to reduce influenza transmission in households – Cluster Randomised Controlled Trial in Germany
The role of facemasks and hand hygiene in the prevention of influenza transmission in households: results from a cluster randomised trial; Berlin, Germany, 2009-2011
Suess T, Remschmidt C, Schink SB, et al. BMC Infectious Diseases 2012, 12:26; Published: 26 January 2012
The rationale for this study, which was carried out over two influenza seasons 2009 (pandemic) and 2010-2011 (post-pandemic) in Berlin was to investigate the efficacy, acceptability, and tolerability of the use of facemasks and intensified hand hygiene in reducing influenza transmission in households with influenza index patients. The authors approached this by conducting a cluster-randomized controlled trial over two seasons: during the pandemic influenza season 2009/10 and the ensuing influenza season 2010/11. The clusters were households with an influenza positive index case in the absence of further respiratory illness within the preceding 14 days. There were three study arms: individuals wearing a facemask and practicing intensified hand hygiene (MH group), individuals wearing facemasks only (M group) and none of the two (control group). Each participating physician received a list of random numbers with the interventions represented in a 1:1:1 ratio. The resulting intervention was only communicated to the households with the physicians (as well as laboratory personnel) blinded from the randomisation results.
The primary outcome measure for secondary cases was PCR-confirmed influenza infection. A secondary outcome measure was the occurrence of ILI as defined by fever plus cough or sore throat. The authors used daily questionnaires to examine adherence and tolerability of the interventions. Participants of the M and MH groups also recorded daily adherence with facemasks, i.e. if they wore masks “always”, “mostly”, “sometimes” or “never” in the situation they had been asked to wear them. In the season 2010/11 they also recorded the number of masks used per day. Participants of the MH households additionally noted the number of hand disinfections per day.
A total of 84 households were recruited in the study (30 out of 82 eligible control household, 26 out of 69 mask-wearing and 28 out of 67 mask and hand hygiene). There were 218 household contacts to the 84 primary cases. There was careful instruction in technique and intense follow-up as described in the provisional open-access paper with nasal sampling of all family members. There was no interference in conventional care and as a consequence a number of the index patients received antivirals, especially in the second season when also a number of index patients and contacts were immunised. In 2009/10 all 41 index cases had an influenza A(H1N1)pdm09 infection while in 2010/11 24 index cases had an A(H1N1)pdm09 infection and 20 index cases had a B infection. The total secondary attack rate was 16% (35/218) by laboratory confirmation and 12% (26/318) by ILI symptoms.
There was no statistically significant effect of the M and MH interventions on secondary infections in an intention-to-treat analysis, but when households where intervention was implemented within 36 hours after symptom onset of the index case were analysed, secondary infection in the pooled mask-wearing and mask and hand hygiene groups was significantly lower compared to the control group (adjusted odds ratio 0.16, 95% CI, 0.03-0.92). In a per-protocol analysis the odds ratios were significantly reduced among participants of the M group compared to controls (adjusted odds ratio, 0.30; 95% CI 0.10-0.94). In addition, with the exception of MH group in 2010/11, adherence to the intervention was reasonable for adults and children, contacts and index cases.
Despite the intention to treat analysis being inconclusive in their analysis the authors conclude that their results support the view that household transmission of influenza can be reduced by the use of these personal measures (use of facemasks and intensified hand hygiene) when used diligently.
ECDC Comment (6 February 2012):
The particular strengths of this study established quickly after the start of the 2009 pandemic include laboratory confirmation of primary and secondary cases with qRT-PCR, the serial testing of all household members over the study period irrespective of respiratory symptoms and the low degree of ‘contamination’ between the groups.
The conduct of RCTs (Randomised Controlled Trials) to evaluate the efficacy of personal measures in different settings (households, hospitals, etc) to prevent the transmission of influenza is difficult (1-3). There are many methodological problems, including among them:
- The time to confirmation of infection and recruitment allows a considerable window when transmission can take effect
- Adherence to the interventions and the impact of the surrounding behavioural practices (sometimes mask-wearing (2), in other settings the opposite(3))
- Difficulties in allowing for asymptomatic infection without serial serological collection (4)
- A need to get the study going early in an epidemic or pandemic before transmission wanes
This study makes an important contribution, not least as it one of the first such studies in a European setting. It is possible to take a purist approach to work like this and conclude there is no unequivocal evidence of efficacy from randomised trials analysed strictly. However it is important to consider all the evidence from trials like this, observational studies (1) and challenge studies such as the EMIT Study (5). On balance these varied approaches suggest that the use of personal measures will reduce transmission of seasonal or pandemic influenza in the home (1).
1. Bin-Reza, Nicoll A, Lopez Chavarrias V, Chamberland M. (2011). The use of masks and respirators to prevent transmission of influenza: a systematic review of the scientific evidence. Influenza and Other Respiratory Viruses DOI: 10.1111/j.1750-2659.2011.00307.x. http://onlinelibrary.wiley.com/doi/10.1111/j.1750-2659.2011.00307.x/abstract
2. 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
3. Cowling B, Chan K-H, Fang VJ, Cheun CYK, Fung ROP, Wai W. et al. Facemasks and hand hygiene to prevent influenza transmission in households: a cluster randomized trial Annals of Internal medicine 2009; 151: 437-446 http://www.annals.org/cgi/reprint/151/7/437
4. Johnson S, Ihekweazu C, Hardelid P, Raphaely N, Hoschler K, Bermingham A, et al. Seroepidemiologic study of pandemic influenza (H1N1) 2009 during outbreak in boarding school, England. Emerg Infect Dis 2011; 17: 1670-77 http://dx.doi.org/10.3201/eid1709.100761
5. Killingley B, Enstone J, Greatorex J, Gilbert A, Lambkin-Williams R, Cauchemez S et al. Use of a Human Influenza Challenge Model to Assess Person-to-Person Transmission:Proof-of-Concept Study. J Inf Dis 2011; (2012) 205 (1): 35-43. doi: 10.1093/infdis/jir701 http://jid.oxfordjournals.org/content/205/1/35.full?sid=372ff475-9447-4412-84a0-1bd820b4b8b0