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Definition of Infection, opportunistic
Medically reviewed by Min Clinic Staff | Updated: January 2026
Infection, opportunistic: An infection that grasps the opportunity to cause disease, which is presented when a person's immune system is weak. These opportunistic microorganisms may be dormant in the body and may cause few problems for healthy individuals. Opportunistic infections are a particular problem for organ transplant patients and those with diseases that affect the immune system, particularly AIDS. Toxoplasmosis and cytomegalovirus are examples of opportunistic infections.