• Abbreviated as FUO

• FUO = fever of unknown origin

The following 3 criteria were the original definition of FUO: ^{(Petersdorf 1961)}

1. Fever > 101°F (38.3°C),
2. Illness > 3 weeks in duration, and
3. No diagnosis after 1 week of hospitalization

• Approach to adult patient with FUO (American Academy of Family Physicians)

• Petersdorf RG, Beeson PB. Fever of unexplained origin: report on 100 cases. Medicine (Baltimore). 1961;40:1-30. DOI: 10.1097/00005792-196102000-00001
• Roth AR, Basello GM. Approach to the Adult Patient with Fever of Unknown Origin (open-access, PDF). Am Fam Physician. 2003;68(11):2223-2229.