Merck Manual on aerosolized secretions:
Aerosolized pathogens inhaled into the lower airways as microparticles include Mycobacterium tuberculosis, Legionella sp, and the influenza virus. M. tuberculosis and the influenza virus are transmitted via aerosolized secretions produced by coughing. Although most cases of pneumococcal pneumonia are acquired by aspiration, in rare cases, especially in an epidemic, the organism is inhaled. Legionella infection is not transmitted from person to person, but rather, is acquired by inhaling infected aerosols from a waterborne source (eg, from air conditioners or shower heads). Waterborne organisms may also be introduced into the lower airways by instrumentation or delivered by small-particle aerosols from a contaminated reservoir nebulizer used with ventilation equipment.
So, if IBD is "airborne" this is not the same as breathing the same air. They would have to be housed together, like said I said above.