What is a systemic infection?

Disseminated: The word "systemic" refers to something that affects the entire body. For example, you could have a "localized" staph infection, in which the infection was confined to a skin abscess, or you could have a "systemic" staph infection, in which the bacteria was present in the blood and multiple organs. In general, systemic infections are more severe than localized infections.

Depends: A "systemic infection" can mean either than an infection has affected the whole body and many organ systems, or it can mean that the body is reacting to an infection in a localized place, like a pneumonia, with signs like fever, fast heart rate and fast breathing rate. So, it depends on what "systemic" means.