Dissemination of microbial aerosols to a suitable portal of entry, usually the respiratory tract. The route of transmission of TB is airborne through droplets containing TB bacilli produced by TB patients when coughing, sneezing, singing or talking. These droplets evaporate and become droplet nuclei which may remain suspended in the air for several hours and may be inhaled by others

A means of spreading infection when airborne droplet nuclei (small particle residue of evaporated droplets ≤5 μm in size containing microorganisms that remain suspended in air for long periods of time) are inhaled by the susceptible host.