Merriam-Webster Collegiate Dictionary - infection

 noun  Date: 14th century  1. the act or result of affecting injuriously  2. an infective agent or material contaminated with an infective agent  3.  a. the state produced by the establishment of an infective agent in or on a suitable host  b. a disease resulting from ~  4. an act or process of infecting; also the establishment of a pathogen in its host after invasion  5. the communication of emotions or qualities through example or contact