Researchers Explore Role of Masks in Preventing Influenza Transmission

Influenza virus is responsible for annual epidemics worldwide and causes a significant public health burden. Influenza virus is transmitted by direct contact with infected individuals, exposure to virus-contaminated objects (fomites), and inhalation of infectious aerosols. The threat of a severe H5N1 pandemic caused by avian influenza and the recent worldwide spreading of influenza H1N1v have renewed interests in non-pharmaceutical interventions for limiting influenza transmission. Hand sanitizers, facemasks and respirators have been stockpiled during pandemic preparedness and are currently recommended in several countries. However, data on their effectiveness for limiting transmission are scarce. Five randomized trials evaluating facemasks and hand hygiene with different designs and objectives have been recently published; three of these trials were conducted in families and did not show significant improvements in their primary analyses in intervention groups versus the control groups; however, in these trials, secondary analysis suggested that intervention using face masks could have a significant effectiveness if implemented rapidly from illness onset or providing a good adherence to the intervention.

Facemasks and respirators have been stockpiled during pandemic preparedness. However, data on their effectiveness for limiting transmission are scarce. Canini, et al. (2010) evaluated the effectiveness of facemask use by index cases for limiting influenza transmission by large droplets produced during coughing in households.

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 seven days. In the intervention arm, the index case had to wear a surgical mask from the medical visit and for a period of five 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.

The researchers 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 percent) of the contacts in the intervention arm and in 25/158 (15.8 percent) of the contacts in the control arm and the difference between arms was 0.40 percent (95 percent CI: 10 percent to 11 percent, P = 1.00). The researchers say they observed a good adherence to the intervention. In various sensitivity analyses, they did not identify any trend in the results suggesting effectiveness of facemasks.

The researchers conclude, Although our findings did not suggest that face masks could prevent transmission of influenza in households, the lack of statistical power prevents us to draw a formal conclusion as to exclude that face masks could nevertheless have a substantial effect. Therefore, our study should be interpreted cautiously as providing additional data to other trials realized in the context of seasonal epidemics.

The researchers say this study should be interpreted with caution since the lack of statistical power prevents them from drawing a formal conclusion regarding effectiveness of facemasks in the context of a seasonal epidemic.

Reference: Canini L, Andréoletti L, Ferrari P, D'Angelo R, BlanchonT, Lemaitre M, Filleul L, Ferry JP, Desmaizieres M, Smadja S, Valleron AJ and Carrat F. Surgical Mask to Prevent Influenza Transmission in Households: A Cluster Randomized Trial. PLoS ONE 5(11): e13998. doi:10.1371/journal.pone.0013998