opportunistic infection

n.

1. An infection by a microorganism that normally does not cause disease but becomes pathogenic when the body’s immune system is impaired and unable to fight off infection, as in AIDS and certain other diseases.

1. An infection by a microorganism that normally does not cause disease but does so when lowered resistance to infection is caused by the impairment of the body’s immune system.

An infection caused by a microorganism that under normal conditions would not bring about disease. Opportunistic infections occur when the body’s immune system is weakened by disease or malnutrition. (See AIDS.)