With the emergence of new and the mutation of wellknown pathogens causatives of epidemics and pandemics the hospitals become in the front line of the attempt to control and stop the disease spread. Pathogens may be present in the air exhaled by an infected person. Ventilation becomes one of the major methods used nowadays for reduction and control the spread of pathogens via the airborne route in hospital premises (Streifel 1999, Kaushal et al. 2004, Beggs et al. 2008).