Infection

The entry and development or multiplication of an infectious agent in the body of man or animals (2,100). It also implies that the body responds in some way to defend itself against the invader, either in the form of an immune response (evidence of this may not be readily available) or disease. An infection does not always cause illness.

There are several levels of infection: Colonization (e.g., S. aureus in skin and normal nasopharynx); subclinical or inapparent infection (e.g. polio); latent infection (e.g. virus of herpes simplex); and manifest or clinical infection.