  Airborne infection risk analysis is usually performed for enclosed spaces
where susceptible individuals are exposed to infectious airborne respiratory
droplets by inhalation. It is usually based on exponential, dose-response
models of which a widely used variant is the Wells-Riley (WR) model. We revisit
this infection-risk estimate and extend it to the population level. We use an
epidemiological model where the mode of pathogen transmission, either airborne
or contact, is explicitly considered. We illustrate the link between
epidemiological models and the WR model. We argue that airborne infection
quanta are, up to an overall density, airborne infectious respiratory droplets
modified by a parameter that depends on biological properties of the pathogen,
physical properties of the droplet, and behavioural parameters of the
individual. We calculate the time-dependent risk to be infected during the
epidemic for two scenarios. We show how the epidemic infection risk depends on
the viral latent period and the event time, the time infection occurs. The
infection risk follows the dynamics of the infected population. As the latency
period decreases, infection risk increases. The longer a susceptible is present
in the epidemic, the higher is its risk of infection by equal exposure time to
the mode of transmission.
