FUO types

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Q: Which of the following is not a type of Fever of Unknown Origin (FUO)?

A) Classic FUO

B) Healthcare-associated FUO

C) Immunocompromised patients' FUO

D) Fictitious FUO

E) Travel-associated FUO

Answer: D

Multiple definitions of FUO have been proposed, but at its core, FUO is the fever in the absence of an identifiable cause despite reasonable evaluation for at least 3 weeks, above temperature >38.3°C. This definition describes classic FUO (choice A).

Healthcare-associated FUO

• ICU patient - Temperature >38.3°C (100.9°F) recorded several times in an ICU patient despite ≥3 days of investigations. The fever must not have been present or incubated upon admission.
• Non-ICU patient - Same definition as for ICU patients, except the patient is hospitalized but not critically ill.
• Post-operative patient—The same definition as for ICU patients applies, except fever is usually defined as ≥38.0°C (100.4°F).

FUO in immunocompromised patients

• Neutropenic patients - Temperature ≥38.3°C (100.9°F) or ≥38.0°C (100.4°F) sustained over one hour, recorded on several occasions over at least 3 days, despite appropriate antimicrobial therapy. Neutropenia is <500 neutrophils/microL or impending fall to that level within 48 hours.
• Patients with HIV and CD4 count <200 cells/microL - Despite appropriate evaluation, temperatures≥38.3°C (100.9°F) were recorded on several occasions for >3 weeks for outpatients or >3 days for inpatients.

Travel-associated FUO

A temperature>38.3°C (100.9°F) was recorded on several occasions for >3 weeks, despite 3 outpatient clinic evaluations, 1 week of intensive outpatient investigation, or 3 days of hospital-based evaluation, in a patient who traveled to another country, typically within the prior 12 months.

Although patients can have a fictitious fever, it is not a part of officially described types (at least yet) - Choice D

#ID

References:

1. Wright WF, Mulders-Manders CM, Auwaerter PG, et al. Fever of unknown origin (FUO) – A call for new research standards and updated clinical management. Am J Med 2022; 135:173.

Adapted from:

2. Wright W, Mackowiak P. Fever of unknown origin. In: Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 8th ed, Bennett J, Dolin R, Blaser M (Eds), Elsevier Saunders 2015. p. 721.

3. Haidar G, Singh N. Fever of Unknown Origin. N Engl J Med. 2022; 386:463.

4. Wright WF, Auwaerter PG. Fever and fever of unknown origin: Review, recent advances, and lingering dogma. Open Forum Infect Dis 2020; 7:ofaa132.

5. Durack DT, Street AC. Fever of unknown origin – reexamined and redefined. Curr Clin Top Infect Dis 1991; 11:35.