An infection that occurs more frequently or is more severe in people with weakened immune systems — such as people with HIV or those receiving chemotherapy — than in people with healthy immune systems.
Opportunistic infections that are common in people with AIDS include: Pneumocystis jiroveci pneumonia (PCP); cryptosporidiosis; histoplasmosis; toxoplasmosis; other parasitic, viral, and fungal infections; and some types of cancers.