title: Surgical mask to prevent influenza transmission in households: a cluster randomized trial.
abstract: BACKGROUND
  Facemasks and respirators have been stockpiled during pandemic preparedness. However, data on their effectiveness for limiting transmission are scarce. We evaluated the effectiveness of facemask use by index cases for limiting influenza transmission by large droplets produced during coughing in households.
  
  
  RESULTS
  A cluster randomized intervention trial was conducted in France during the 2008-2009 influenza season. Households were recruited during a medical visit of a household member with a positive rapid influenza A test and symptoms lasting less than 48 hours. Households were randomized either to the mask or control group for 7 days. In the intervention arm, the index case had to wear a surgical mask from the medical visit and for a period of 5 days. The trial was initially intended to include 372 households but was prematurely interrupted after the inclusion of 105 households (306 contacts) following the advice of an independent steering committee. We used generalized estimating equations to test the association between the intervention and the proportion of household contacts who developed an influenza-like illness during the 7 days following the inclusion. Influenza-like illness was reported in 24/148 (16.2%) of the contacts in the intervention arm and in 25/158 (15.8%) of the contacts in the control arm and the difference between arms was 0.40% (95%CI: -10% to 11%, P = 1.00). We observed a good adherence to the intervention. In various sensitivity analyses, we did not identify any trend in the results suggesting effectiveness of facemasks.
  
  
  CONCLUSIONS
  This study should be interpreted with caution since the lack of statistical power prevents us to draw formal conclusion regarding effectiveness of facemasks in the context of a seasonal epidemic.
  
  
  BACKGROUND
  clinicaltrials.gov NCT00774774.
authors.affiliation: UMR-S 707, UPMC-Paris 6, Paris, France.
authors.forename: Laetitia
authors.initials: L
authors.lastname: Canini
authors.forename: Laurent
authors.initials: L
authors.lastname: Andréoletti
authors.forename: Pascal
authors.initials: P
authors.lastname: Ferrari
authors.forename: Romina
authors.initials: R
authors.lastname: D'Angelo
authors.forename: Thierry
authors.initials: T
authors.lastname: Blanchon
authors.forename: Magali
authors.initials: M
authors.lastname: Lemaitre
authors.forename: Laurent
authors.initials: L
authors.lastname: Filleul
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Ferry
authors.forename: Michel
authors.initials: M
authors.lastname: Desmaizieres
authors.forename: Serge
authors.initials: S
authors.lastname: Smadja
authors.forename: Alain-Jacques
authors.initials: AJ
authors.lastname: Valleron
authors.forename: Fabrice
authors.initials: F
authors.lastname: Carrat
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D003371:Cough / Q000821:virology; D005191:Family Characteristics; D005260:Female; D005602:France / Q000453:epidemiology; D006801:Humans; D053122:Influenza A Virus, H3N2 Subtype; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control* / Q000635:transmission; D008297:Male; D008397:Masks / Q000009:adverse effects / Q000706:statistics & numerical data*; D017063:Outcome Assessment, Health Care / Q000706:statistics & numerical data; D010146:Pain / Q000209:etiology; D058873:Pandemics / Q000517:prevention & control*; D012621:Seasons; D055815:Young Adult