Comprehensive Approach to Infectious Workup
The infectious workup should follow a systematic approach that includes appropriate specimen collection, microbiological testing, and imaging based on the suspected source of infection, with prompt initiation of empiric antimicrobial therapy while awaiting culture results. 1
Initial Assessment and Specimen Collection
Clinical Evaluation
- Assess for signs of sepsis, including fever, tachycardia, hypotension, tachypnea, altered mental status
- Evaluate for potential source of infection (respiratory, abdominal, urinary, skin/soft tissue, etc.)
- Document recent procedures, implanted devices, or immunocompromised status
Essential Specimens to Collect
Blood cultures
- Collect at least two sets from different sites before antibiotic administration 1
- Additional sets may be needed for suspected endocarditis or vascular infections
Site-specific specimens
- Respiratory: Sputum (purulent sample preferred), nasopharyngeal swabs, bronchoalveolar lavage (BAL) if indicated 1
- Urine: Clean-catch midstream or catheterized sample
- Wounds/Soft tissue: Aspirate or tissue biopsy (not surface swabs when possible)
- Intra-abdominal: Fluid/tissue sampling during source control procedures 1
- Pleural fluid: Diagnostic thoracentesis for significant effusions 1
Laboratory Testing
Basic Workup
- Complete blood count with differential
- Comprehensive metabolic panel
- C-reactive protein and procalcitonin (if available)
- Lactate level (for suspected sepsis)
- Urinalysis and urine culture
Specialized Testing Based on Clinical Presentation
- Respiratory pathogens panel for respiratory symptoms
- Legionella urinary antigen for severe pneumonia 1
- COVID-19 testing per institutional guidelines 1
- Specific serological or molecular tests based on epidemiological factors
Imaging Studies
Selection Based on Suspected Source
- Chest: Chest X-ray or CT for respiratory symptoms
- Abdomen/Pelvis: CT scan for suspected intra-abdominal infection
- Soft tissue: Ultrasound or MRI for suspected necrotizing infections
- Central nervous system: CT or MRI for suspected CNS infection
Source Control
Prompt Identification and Control
- Identify the infectious source through clinical, laboratory, and imaging findings 1
- Implement source control measures within 6-12 hours of diagnosis 1
- For necrotizing infections, urgent surgical debridement is essential 2
- For intra-abdominal infections, drainage or debridement of the infectious source is critical 1
Surgical Consultation
- Early surgical consultation for suspected surgical infections
- Immediate surgical intervention for necrotizing soft tissue infections 2
- Consider drainage procedures for abscesses or empyemas
Antimicrobial Therapy
Empiric Therapy
- Initiate broad-spectrum antibiotics within 1 hour of recognizing sepsis 1
- Select empiric regimen based on:
- Suspected source of infection
- Local antibiogram and resistance patterns
- Patient risk factors for resistant organisms
- Severity of illness
De-escalation and Duration
- Narrow antibiotic spectrum once culture results are available 1
- For uncomplicated infections with adequate source control, short courses (4-7 days) are often sufficient 1
- For complicated infections, duration depends on clinical response and source control adequacy 3
Special Considerations
Resource-Limited Settings
- Focus on essential diagnostics: blood cultures, Gram stain, and basic laboratory tests 1
- Prioritize source control and timely antimicrobial therapy
- Consider empiric therapy based on local epidemiology when diagnostic capabilities are limited
Immunocompromised Patients
- More extensive workup including fungal and opportunistic pathogens
- Lower threshold for bronchoscopy and invasive diagnostic procedures
- Broader empiric antimicrobial coverage
Monitoring and Follow-up
- Daily reassessment of antimicrobial therapy appropriateness 1
- Monitor clinical response, inflammatory markers, and culture results
- Repeat imaging for non-resolving infections
- Consider infectious disease consultation for complex cases or treatment failure
Common Pitfalls to Avoid
- Delaying antimicrobial therapy while awaiting cultures in severely ill patients
- Inadequate source control (partial drainage, incomplete debridement)
- Failure to obtain appropriate cultures before starting antibiotics
- Overly prolonged antibiotic courses when adequate source control has been achieved
- Not considering unusual or resistant pathogens in patients with healthcare exposure or recent antibiotic use
By following this systematic approach to infectious workup, clinicians can efficiently diagnose and manage infections, leading to improved patient outcomes and reduced mortality.