Definitions • Contact transmission: There are two subgroups of contact transmission: direct and indirect. Direct transmission occurs when influenza is transferred by contact from an infected person to another person without a contaminated intermediate object. Indirect transmission involves the transfer of influenza by contact with a contaminated intermediate object. In both, contaminated hands play an important role in carrying influenza to mucous membranes. • Droplet Spray transmission: person-to-person transmission of influenza through the air by droplet sprays. A key feature is deposition by impaction on exposed mucous membranes. • Aerosol transmission: person-to-person transmission of influenza through the air by aerosols in the inspirable (inhalable) size range or smaller. Particles are small enough to be inhaled into the oronasopharynxand distally into the trachea and lung.