Pilot study: A simple calculation of the SAR is given by dividing the number of household contacts with influenza by the total number of household contacts. To estimate the anticipated SAR of 0.241 to within ±5% would require 283 household contacts. Given an average household size of 3.8 (i.e. 2.8 contacts per household) we would require at least 101 households in the placebo group; we propose to recruit 130 households in this arm to allow for some households being lost to follow-up. To test the randomization and intervention procedures we will recruit a further 35 households to the second and third study arms (masks and hand-hygiene). This will also enable a preliminary estimate of the efficacy of hand hygiene and masks although the power of the pilot study will be low to detect small or medium effect sizes with statistical significance. More importantly, the pilot study will allow an idea of the feasibility of these interventions, and coherence to them.