Acute fever

Background

Definition

• Defined as temperature ≥38°C (100.4°F).
• Peripheral temperature is not clinically accurate and central measurements are the preferred means of determining fever.
  • Rectal or oral
  • Rectal temperatures should not be performed in neutropenic patients

Clinical Features

• Fever directly causes an increase in:
  • Heart rate: 10 beats per minute per degree centigrade
  • Respiratory rate

Differential Diagnosis

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Fever

Infectious

• Critical
  • Sepsis
  • PNA with respiratory failure
  • Peritonitis
  • Meningitis
  • Cavernous Sinus Thrombosis
  • Necrotizing Fasciitis
• Emergent
  • PNA
  • Peritonsillar Abscess
  • Retropharyngeal Abscess
  • Epiglottitis
  • Endocarditis
  • Pericarditis
  • Appendicitis
  • Cholecystitis
  • Diverticulitis
  • Intra-abdominal abscess
  • Pyelonephritis
  • Tubo-ovarian abscess
  • Encephalitis
  • Brain abscess
  • Cellulitis
  • Abscess
  • Malaria
• Non-emergent
  • Viral syndrome
  • Otitis Media
  • Sinusitis
  • Pharyngitis
  • Influenza
  • TB
  • UTI
  • Epididymitis
  • Prostatitis

Non-infectious

• Critical
  • AMI
  • PE
  • Intracranial Hemorrhage
  • CVA
  • NMS
  • Thyroid Storm
  • Acute Adrenal Insufficiency
  • Transfusion Rx
  • Pulmonary Edema
  • Heat Stroke
  • Malignant hyperthermia
• Emergent
  • CHF
  • Dehydration
  • Recent Seizure
  • Sickle Cell Dz
  • Transplant rejection
  • Pancreatitis
  • DVT
  • Serotonin Syndrome
• Non-emergent
  • Drug fever (except as in NMS and Serotonin Syndrome)
  • Malignancy
  • Gout
  • Sarcoidosis
  • Crohn's Disease
  • Postmyocardiotomy syndrome
  • Sweet's syndrome

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DDx by Heart Rate

Every 0.55°C increase in temperature should → increase HR by ~10BPM

• If patient has relative bradycardia, consider:
  • Concomitant medication
  • Drug fever
  • Typhoid Fever
  • Brucellosis
  • Leptospirosis
• If patient has frank bradycardia, consider:
  • Rheumatic Fever
  • Lyme Disease
  • Viral Myocarditis
  • Endocarditis

Evaluation

General Approach

• History: duration, recent travel, sick contacts, immunocompromised status, medications, recent procedures/hospitalizations, indwelling devices
• Physical exam: systematic search for source — HEENT (sinuses, pharynx, ears, dental), lungs, heart, abdomen, skin/wounds, GU, joints, spine
• Not all fevers require a workup — well-appearing immunocompetent adults with clear viral URI symptoms may need only supportive care

Workup (when indicated)

• Basic: CBC with differential, BMP, urinalysis, blood cultures (x2 if concern for bacteremia), CXR
• Additional based on suspicion:
  • Lactate, procalcitonin — if sepsis suspected
  • Lumbar puncture — if meningitis/encephalitis suspected
  • CT imaging — guided by suspected source (abdomen/pelvis for abdominal source, CT chest for pulmonary, CT head if AMS)
  • LFTs, lipase — if hepatobiliary or pancreatic source suspected
  • Joint aspiration — if septic arthritis suspected
  • Wound cultures — if skin/soft tissue infection

Special Populations Requiring Lower Threshold for Workup

• See Pediatric fever of uncertain source for infants and children
• See Neutropenic fever for oncology patients
• See AIDS fever of unknown origin for HIV/AIDS patients
• See Fever in traveler for returned travelers
• See Fever and rash for fever with associated rash

Management

• Antipyretics:
  • Acetaminophen 650-1000 mg PO/IV q4-6h (max 4g/day)
  • Ibuprofen 400-800 mg PO q6-8h
  • Antipyretics improve comfort but do not treat the underlying cause
  • Fever itself is generally not harmful in immunocompetent adults (except in hyperthermia where temperature >41C/106F can cause organ damage)
• Treat the underlying condition:
  • Empiric antibiotics if bacterial infection suspected — do not delay for cultures
  • Source control (I&D of abscesses, removal of infected lines/devices)
  • See specific disease pages for targeted management
• Fluid resuscitation: Fever increases insensible losses; ensure adequate hydration
• Avoid "fever phobia": In immunocompetent patients, aggressive fever treatment is not required and may mask clinical trends

Disposition

• Admit:
  • Suspected sepsis or bacteremia
  • Immunocompromised with fever (neutropenic fever)
  • Hemodynamic instability
  • Identified source requiring IV antibiotics or surgical intervention
  • Unreliable follow-up with concerning clinical picture
• Discharge:
  • Well-appearing with clear viral syndrome
  • Identified source amenable to outpatient treatment (uncomplicated UTI, mild cellulitis)
  • Reliable follow-up with clear return precautions
  • Return precautions: worsening symptoms, inability to tolerate PO fluids, rigors, altered mental status

See Also

• Pediatric fever of uncertain source
• Fever and rash
• Fever of unknown origin
• Neutropenic fever
• AIDS fever of unknown origin
• Environmental heat diagnoses
• Fever in traveler