What is the appropriate diagnostic and therapeutic approach for a patient presenting with intermittent fever?

Clinical Vignette: Intermittent Fever in a Critically Ill Patient

Patient Presentation

A 58-year-old man with a history of aortic valve replacement 3 years ago presents to the ICU on post-operative day 5 following exploratory laparotomy for bowel obstruction. He develops fever to 39.2°C (102.6°F) that occurs intermittently every 12-18 hours, with periods of defervescence in between. 1

Initial Clinical Features

• Vital signs during febrile episodes: Temperature 39.2°C, heart rate 118 bpm, blood pressure 142/88 mmHg, respiratory rate 22 breaths/min, oxygen saturation 94% on 2L nasal cannula 1
• Physical examination reveals: Surgical wound with minimal erythema, no purulent drainage; scattered crackles in bilateral lung bases; no new cardiac murmurs; abdomen soft with mild tenderness at incision site 1, 2
• Medications: Vancomycin and piperacillin-tazobactam started empirically on post-op day 3 for suspected surgical site infection 1

Diagnostic Workup Sequence

Day 5 (Initial Fever Episode)

Immediate actions performed before any imaging or extended workup: 1

• Blood cultures obtained from two separate sites before any antibiotic changes
• Complete blood count showing WBC 14,200/μL with 82% neutrophils
• Comprehensive metabolic panel revealing mild transaminase elevation (ALT 78 U/L, AST 92 U/L)
• Urinalysis and urine culture sent
• Bedside chest radiography performed showing bilateral lower lobe opacities, unchanged from post-operative baseline 1

Day 6 (Persistent Intermittent Fever)

Because fever persists beyond 48 hours despite broad-spectrum antibiotics, escalated diagnostic approach initiated: 1

• Serum procalcitonin level: 3.2 ng/mL (suggesting bacterial infection rather than non-infectious cause) 1
• Abdominal ultrasound performed given the transaminase elevation and recent abdominal surgery, revealing gallbladder wall thickening suggestive of acalculous cholecystitis 1
• Blood cultures from Day 5 remain negative at 48 hours

Day 7 (Continued Fever with New Findings)

CT abdomen/pelvis with IV contrast ordered in collaboration with surgical team (as recommended for post-surgical patients without readily identified etiology): 1

• Confirms acalculous cholecystitis with pericholecystic fluid
• Reveals small fluid collection adjacent to surgical anastomosis site
• No evidence of bowel perforation or abscess formation requiring immediate drainage

Day 8-9 (Broadening Differential)

Given prosthetic valve and persistent fever despite appropriate antibiotics: 1

• Transthoracic echocardiogram performed showing no vegetations, normal valve function
• Repeat blood cultures (third set) obtained
• Fungal serologies sent including 1,3-β-D-glucan and galactomannan (given prolonged antibiotic exposure and ICU stay) 1
• Q fever serologies ordered given valve history and fever pattern (phase I and phase II IgG antibodies) 1

Clinical Course and Diagnosis

Days 10-12

• Percutaneous cholecystostomy tube placed by interventional radiology with drainage of purulent bile
• Bile culture grows Enterococcus faecalis and Klebsiella pneumoniae
• Antibiotic regimen adjusted to ampicillin-sulbactam based on susceptibilities
• Fever pattern begins to improve 36 hours after drainage procedure 1

Day 14

• Patient defervesces completely
• Inflammatory markers trending down (procalcitonin 0.8 ng/mL, WBC 9,200/μL)
• Q fever serologies return negative
• Fungal markers negative 1

Follow-Up Monitoring Plan

Given prosthetic valve and acute Q fever ruled out, but patient remains at lifelong risk: 1

• Serologic monitoring scheduled at 3,6,12,18, and 24 months post-infection
• Patient counseled to seek immediate medical attention for any future fever, fatigue, or new cardiac symptoms
• Baseline ophthalmologic examination not needed (hydroxychloroquine not indicated as Q fever excluded) 1, 3
• Antibiotic course completed for 14 days total after source control 1

Key Clinical Pearls from This Case

This vignette demonstrates the algorithmic approach to intermittent fever in ICU patients: 1

• Initial bedside chest radiography performed despite low positive predictive value, as pneumonia remains most common ICU infection
• CT imaging pursued early in post-surgical patient when initial workup non-revealing
• High-risk features (prosthetic valve) prompted extended infectious workup including Q fever serologies
• Source control (cholecystostomy) proved essential when antibiotics alone failed
• Procalcitonin helped distinguish bacterial infection from non-infectious fever causes 1

The intermittent fever pattern did not exclude serious infection and required persistent diagnostic evaluation until source identified. 1, 2, 4