  Although close contact represents an important contagion route, the mechanism
of exposure to exhaled droplets remains insufficiently characterized. In this
study, an integrated risk assessment is presented for SARS-CoV-2 close contact
exposure between a speaking infectious subject and a susceptible subject. It is
based on a three-dimensional transient numerical model for the description of
exhaled droplet spread once emitted by a speaking person, coupled with a
recently proposed SARS-CoV-2 emission approach. Particle image velocimetry
measurements were conducted to validate the numerical model. The contribution
of large droplets to infection risk is dominant for distances < 0.6 m, whereas
for longer distances, the exposure risk depends only on airborne droplets. In
particular, for short exposures (10 s) a minimum safety distance of 0.75 m
should be maintained to lower the risk below 0.1%; for exposures of 1 and 15
min this distance increases to about 1.0 and 1.5 m, respectively. Based on the
interpersonal distances across countries reported as a function of interacting
individuals, cultural differences, and environmental and sociopsychological
factors, the approach presented here revealed that, in addition to intimate and
personal distances, particular attention must be paid to exposures longer than
1 min within social distances (of about 1 m).
