<unk> al definition<unk>  >38.3 C on<unk> al occasions
Lasting for at least 3 weeks
No clear diagnosis after 1 week inpatient workup
Newer definition - "Prolonged<unk> " with:
3 outpatient visits without identifying a cause or
3 inpatient days without identifying a cause or
1 week of “intelligent and invasive” ambulatory investigation<unk>  >38.3 C on<unk> al occasions
Lasting for at least 3 weeks
No clear diagnosis after 1 week inpatient workup
3 outpatient visits without identifying a cause or
3 inpatient days without identifying a cause or
1 week of “intelligent and invasive” ambulatory investigation
Fever of unknown origin 
Infection
Acute fever
Bacterial
Neutropenic fever
Adenitis
Q fever
Endocarditis