Technically, "bacter(a)emia" refers to bacteria within the blood stream. This would be the case whenever you grow an organism from blood culture.
"Septic(a)emia" actually refers to DIVIDING bacteria in the blood stream. This would indicate a more fulminant state and a worse prognosis.
However, septicaemia is incredibly difficult to prove - growing bacteria on culture only proves that they are dividing in the culture medium, not the blood stream. You virtually have to catch them in the act to call it septicaemia.
However, these are only the technical definitions. Often the two are used interchangably, since there is very little significant clinical difference between the two. Either way, the patient will appear septic (high spiking temperatures, raised inflammatory markers and white cell count, etc.) and is in a poor way.