Table 3. Classification scheme for Gram-negative blood cultures.

Category	Definition
Definite Gram-negative sepsis consequent upon cultured isolate	The blood culture isolate is contributing to the patient’s clinical state and treatment was considered to be required.
Probable Gram-negative sepsis consequent upon cultured isolate	The blood culture isolate is probably contributing to the patient’s clinical state, but there is insufficient evidence to confirm or refute this. Treatment was considered to be required
Possible Gram-negative sepsis consequent upon cultured isolate	The blood culture isolate may be contributing to the patient’s clinical condition, but the patient improved without antibiotics predicted to be active based on antimicrobial susceptibility testing, and it is not possible to confirm or refute definite/probably Gram-negative (GN) sepsis. i.e. Treatment was considered to be required but the patient improved without antibiotics likely to be active against the isolate.
Occult or transient bacteraemia	The blood culture isolate may have contributed to the patient’s clinical condition, but by the time they are assessed with the culture, they have improved. Unlike the definition for ‘possible GN sepsis’, treatment was not considered to be required, but instead a repeat blood culture was desirable.
Definite contaminant	The isolate has never contributed to patient’s condition and was very likely not present in the bloodstream
Probable contaminant	The isolate probably never contributed to patient’s condition and was probably not present in the bloodstream/or there is insufficient evidence to say for sure.