Real Dictionary

infect
verb: To infect people, animals, or plants means to cause them to have a disease or illness.

infect in American English
to contaminate with a disease-producing organism or matter
adjective: infected
intransitive verb: to become infected
transitive verb: to affect or contaminate (a person, organ, wound, etc.) with disease-producing germs

infect in British English
to cause infection in; contaminate (an organism, wound, etc) with pathogenic microorganisms
adjective: contaminated or polluted with or as if with a disease; infected