N contact with secretions that contain the virus, either directly (e.g. hand to hand) from an infected person or indirectly from surfaces (e.g. door knob), N ''large'' airborne droplets, which are produced by an infected person during talking, sneezing, or coughing, and can only spread in air for a distance of less than 1-2 m before falling down, N ''small'' droplet nuclei (dried droplets), that can stay airborne for an extended time and be transported long distances. Despite many years of study, the routes of spread of viral airways infections remain controversial. One opinion is that the virus is transferred through direct contact [6] , while the other is that the virus is transferred through airborne spread [7, 8] . During the SARS epidemic, early preventive messages to the public were to wash hands and, generally to avoid ''direct'' contact spread. Later, analysis of the temporal and spatial distributions of SARS cases in a large community outbreak in Hong Kong and the correlation of these data with the three-dimensional spread of a virus-laden aerosol plume indicated an important role for airborne spread of droplet nuclei [9] .