What is Intermittent Fever?
Intermittent fever is a fever pattern characterized by temperature elevations that rise and fall, returning to normal (or below) at least once during a 24-hour period, distinguishing it from sustained fever where temperature remains continuously elevated. 1
Fever Pattern Classification
Intermittent fever represents one of several distinct fever patterns observed clinically:
- Intermittent fever: Temperature rises above normal and returns to normal or below within each 24-hour cycle 1
- Remittent fever: Temperature fluctuates but never returns to normal baseline 1
- Sustained fever: Temperature remains continuously elevated with minimal variation 1
- Hectic fever: Dramatic temperature swings with wide fluctuations 1
Most febrile patients demonstrate either remittent or intermittent patterns, which typically follow normal diurnal (circadian) variation when caused by infection 1
Clinical Significance and Diagnostic Value
Fever patterns, including intermittent fever, have limited diagnostic utility in determining the underlying cause or predicting bacteremia. 1 A prospective study of 200 consecutive patients referred for infectious disease consultation found that:
- Hectic fevers occurred across all categories of infectious and noninfectious diseases 1
- While hectic patterns appeared more frequently in bacteremic patients, many nonbacteremic subjects had this pattern and many bacteremic patients did not 1
- The exception is sustained fever, which nearly always occurred in patients with Gram-negative pneumonia or CNS damage, though some patients with these conditions had other patterns 1
Common Etiologies of Intermittent Fever
Infectious Causes
The most frequent infectious causes include:
- Focal bacterial infections, particularly those localized to canals (urinary tract, biliary ducts, colon) 2
- Foreign body infections 2
- Less commonly: infective endocarditis, tuberculosis, Yersinia enterocolitica, malaria 2
- Rare causes: borreliosis, rat-bite fever, chronic meningococcemia, chronic Epstein-Barr virus infection 2
Inflammatory and Autoinflammatory Causes
- Adult-onset Still disease and juvenile chronic arthritis are the most common causes of intermittent inflammatory fever 3
- Genetic periodic fever syndromes present with typical intermittent fever patterns 3
- Less common: ankylosing spondylitis, pulmonary embolism, sarcoidosis, Crohn's disease 3
- Rare: vasculitis, polychondritis, Castleman disease 3
Other Causes
- Drug-induced fever is a classical cause of intermittent fever 3
- Factitious fever 3
- Malignancies and autoimmune diseases 4
- Long COVID has been reported as a cause of persistent intermittent fever lasting over a month after acute COVID-19 pneumonia 5
Diagnostic Approach
Careful history and physical examination, combined with simple complementary investigations performed during a febrile episode, are often sufficient to guide further complex investigations. 2
Key diagnostic considerations:
- Intermittent fever frequently appears as the first and isolated sign of disease, presenting a diagnostic challenge 3
- Biological tests and computed tomographic scans are worthwhile diagnostic tools 3
- Follow-up of undiagnosed cases is essential 3
- Recognizing characteristic symptom patterns of autoinflammatory diseases can provide crucial clues for targeted diagnostic testing 4
Temperature Measurement Standards
For accurate fever assessment in critically ill patients:
- Central temperature monitoring (pulmonary artery catheter thermistors, bladder catheters, or esophageal balloon thermistors) is preferred when these devices are in place 6
- For patients without central monitoring, oral or rectal temperatures are preferred over less reliable methods (axillary, tympanic, temporal artery, or chemical dot thermometers) 6
- The SCCM/IDSA defines fever as a single temperature measurement ≥38.3°C 6