Types of Fever

Classification by Duration

Classification by Temperature Pattern

1. Continued (Sustained) Fever

• Temperature remains consistently elevated above normal throughout the day
• Fluctuation is less than 1°C (1.5°F) over 24 hours and never touches normal
• Classic examples: Typhoid fever (step-ladder rise in week 1, then sustained), lobar pneumonia, urinary tract infection
• "Clinically characterized by a typical continuous fever for 3 to 4 weeks" - Park's Textbook of Preventive and Social Medicine

2. Remittent Fever

• Temperature fluctuates more than 2°C over 24 hours but never returns to normal
• The most common type of fever in clinical practice
• Classic examples: Infective endocarditis, most viral fevers, brucellosis
• Pel-Ebstein fever (a subtype seen in Hodgkin lymphoma) is sometimes considered a remittent/relapsing variant

3. Intermittent Fever

• Temperature is elevated for only a few hours per day, then returns to normal
• The period of fever is called a paroxysm
• Classic example: Malaria, pyogenic abscesses, septicemia
• Sub-types based on timing:
  • Quotidian - paroxysm every day (P. falciparum, P. knowlesi)
  • Tertian - paroxysm every alternate day / every 48 hours (P. vivax, P. ovale, P. falciparum in some)
  • Quartan - paroxysm every 72 hours with 2 days between attacks (P. malariae)
• "When a paroxysm of intermittent fever occurs daily, it is called quotidian, when on alternate days it is called tertian and when two days intervene between the consecutive attacks, it is called quartan." - S. Das, A Manual on Clinical Surgery

4. Hectic (Septic) Fever

• Extreme form of intermittent or remittent fever
• Very wide swings in temperature (>5°C), often with drenching sweats, rigors, and marked chills
• Classic examples: Kala-azar (visceral leishmaniasis), pyaemia, hepatic abscess
• Sometimes called "picket fence" pattern - "The classic initial symptoms of lateral sinus thrombosis include a picket fence fever pattern (diurnal temperature spikes that exceed 103°F/39.4°C)" - Cummings Otolaryngology

5. Relapsing (Recurrent) Fever

• Episodes of fever (days) separated by afebrile intervals (days), then recurring
• Examples:
  • Borrelia relapsing fever - days of fever, then a several-day afebrile period, then relapse
  • Brucellosis - undulant fever, waves of fever and remission
  • Malaria (certain species)
• Harrison's Principles of Internal Medicine (22nd ed.) notes: "Another relapsing fever is related to Borrelia infection, with days of fever followed by a several-day afebrile period and then a relapse into additional days of fever."

Special Named Fever Patterns

Classification by Cause (Etiology)

Fever of Unknown Origin (FUO)

Mechanism (Physiology)

• S. Das, A Manual on Clinical Surgery, 13th ed.
• Harrison's Principles of Internal Medicine, 22nd ed. (2025)
• Goldman-Cecil Medicine, International Edition
• Costanzo Physiology, 7th ed.
• Medical Microbiology, 9th ed.
• Park's Textbook of Preventive and Social Medicine
• Cummings Otolaryngology

Diagnosis and Treatment of Fever

PART 1: DIAGNOSTIC APPROACH

Step 1 - History Taking

• Duration and pattern of fever (helps narrow the type as discussed previously)
• Associated symptoms - cough, dysuria, rash, joint pain, diarrhea, headache, neck stiffness
• Travel history - geographic exposures (malaria, dengue, typhoid endemic areas)
• Animal/insect exposure - tick bites, cat scratches, rodent contact
• Medications - new drugs within 2 months (drug fever is common)
• Immunocompromise - HIV, steroids, chemotherapy, transplant
• Vaccination history
• Sexual history - STI risk
• Injection drug use - endocarditis risk

Step 2 - Physical Examination

• Rash - character, distribution, evolution (macular, petechial, purpuric, vesicular)
• Lymphadenopathy - localized vs. generalized
• Organomegaly - hepatomegaly, splenomegaly (malaria, kala-azar, typhoid)
• Meningismus - neck stiffness, Kernig's, Brudzinski's signs
• Heart murmurs - endocarditis
• Skin/soft tissue - cellulitis, abscess, wound infection
• Joints - arthritis, warmth, swelling
• Temperature-pulse relationship - relative bradycardia (pulse-temperature dissociation) seen in typhoid, brucellosis, leptospirosis, drug fever

Step 3 - Laboratory Investigations

Tier 1 - Routine (All Febrile Patients)

Tier 2 - Targeted (Based on Clinical Clues)

Tier 3 - Biomarkers

PART 2: TREATMENT OF FEVER

A. Non-Pharmacological (Physical) Methods

1. Tepid sponging - lukewarm water (not ice cold - causes vasoconstriction and shivering)
2. Cooling blankets - for hyperpyrexia; always used alongside antipyretics, not alone
3. Ice packs over major arteries (axilla, groin) - for hyperthermia/hyperpyrexia >41°C
4. Adequate hydration - oral fluids or IV saline
5. Light clothing, cool environment
6. Misting with tepid water + fan - for temperatures >41°C with neurological risk

B. Pharmacological Treatment - Antipyretics

1. Paracetamol (Acetaminophen) - FIRST LINE

• Dose: 500 mg - 1 g orally every 4-6 hours (max 4 g/day in adults)
• Children: 10-15 mg/kg every 4-6 hours
• Mechanism: Inhibits COX-3 in the CNS and blocks PGE2 synthesis in the hypothalamus
• Preferred because it does not affect platelets or the GI tract
• Available as oral, IV (paracetamol infusion), rectal suppository
• Caution: Hepatotoxic in overdose or chronic alcohol use

2. NSAIDs (Ibuprofen, Aspirin, Naproxen)

• Equally effective to acetaminophen for fever reduction
• Ibuprofen: 200-400 mg every 6-8 hours (adults); 5-10 mg/kg every 6-8 hours (children)
• Aspirin is CONTRAINDICATED in children <19 years with viral illness - risk of Reye syndrome (acute encephalopathy + liver failure)
• NSAIDs can adversely affect platelets and GI tract - use with caution
• Glucocorticoids also reduce fever by blocking phospholipase A2 (preventing arachidonic acid release) AND blocking cytokine mRNA transcription

3. Temperature Threshold for Treatment

C. Treatment of the Underlying Cause

D. Special Situations

• Empiric antibiotics should be avoided in mild, undifferentiated outpatient fever - most are viral
• Watchful waiting is appropriate for non-toxic patients with mild nonspecific symptoms
• Fever in returning traveler - always exclude malaria (can be fatal if missed)
• Neutropenic fever (post-chemotherapy) - emergency; start empiric broad-spectrum antibiotics immediately (Table 260-4 Goldman-Cecil)
• Fever >41°C (hyperpyrexia) - aggressive cooling required; above this level, temperature is usually due to hyperthermia (not true fever), often from CNS hemorrhage or medication

• Harrison's Principles of Internal Medicine, 22nd ed. (2025)
• Goldman-Cecil Medicine, International Edition
• Lippincott Illustrated Reviews: Pharmacology
• Goodman & Gilman's Pharmacological Basis of Therapeutics
• Rosen's Emergency Medicine
• Park's Textbook of Preventive and Social Medicine
• SCCM/IDSA ICU Fever Guidelines