How should the likelihood of bacterial infection be assessed in patients treated with broad-spectrum intravenous antibiotics in the emergency department?

Assessment of Bacterial Infection Likelihood in Patients Receiving Broad-Spectrum IV Antibiotics in the Emergency Department

Biomarkers and clinical assessment should be used to determine the likelihood of bacterial infection in patients treated with broad-spectrum IV antibiotics in the emergency department, as approximately one-third of patients empirically treated with broad-spectrum antibiotics ultimately have non-bacterial conditions. 1

Current State of Empiric Antibiotic Use in the ED

• Studies show that 35% of patients receiving broad-spectrum IV antibiotics in the emergency department (ED) are ultimately found to have unlikely or definitely no bacterial infection 1
• Another study found that only 19.3% of patients with suspected sepsis who received broad-spectrum antibiotics had confirmed bacterial infections, while 35.9% had no evidence of bacterial infection 2
• Broad-spectrum antibiotics are frequently administered despite resistant pathogens being uncommon in community-onset infections (MRSA 11.7%, ceftriaxone-resistant organisms 13.1%) 3

Recommended Diagnostic Approach

Biomarkers for Assessment

• Procalcitonin (PCT) is recommended to guide antibiotic initiation for patients with suspected lower respiratory tract infections, acute exacerbation of asthma, and COPD who are likely to be admitted to the hospital 4
• C-reactive protein (CRP) is not recommended for guiding antibiotic initiation for respiratory tract infections in the ED due to very low-quality evidence 4
• Blood cultures should be obtained before starting antimicrobial therapy to enable tailoring of treatment and de-escalation of broad-spectrum antibiotics 4

Imaging and Clinical Evaluation

• Appropriate clinical examination and imaging are crucial for reaching an accurate diagnosis quickly 4
• For patients with prolonged fever and neutropenia at high risk for invasive fungal disease, CT of the lungs is strongly recommended 4
• Consider abdominal imaging in patients without localizing signs or symptoms who are at high risk for invasive fungal disease 4

Risk-Based Approach to Antibiotic Administration

• For patients with septic shock or bacterial meningitis, prompt administration of effective antibiotics is supported by evidence 5
• For less severe infectious syndromes, withholding antibiotic therapy until diagnostic results are available (e.g., 4-8 hours) appears acceptable in most cases 5
• Both inadequate and unnecessarily broad empiric antibiotics are associated with higher mortality (odds ratios 1.19 and 1.22, respectively) 3

Antimicrobial Stewardship Considerations

• The ED plays a key role in ensuring collection of appropriate cultures before initiating antimicrobial therapy 4
• Watchful waiting (no prescription, delayed prescription, or non-antibiotic treatment) with appropriate monitoring can be considered for patients with potentially self-resolving infections 4
• De-escalation strategies should be implemented to transition patients from empiric broad-spectrum antibiotics to targeted narrow-spectrum therapy as soon as possible 4

Common Pitfalls and Caveats

• Broad-spectrum antibiotics appear to be associated with increased mortality, longer hospital stays, greater costs, and increased Clostridioides difficile infection in community-onset pneumonia 6
• Systemic inflammatory response syndrome (SIRS) criteria and Quick Sequential Organ Failure Assessment (qSOFA) scores ≥2 were not associated with the presence of bacterial infections in one study 2
• The most frequent post-hoc diagnoses in patients without bacterial infection include viral infections (28%), volume overload or cardiac disease (9%), drug effects (9%), and hypovolemia (7%) 1
• Adverse events from broad-spectrum antibiotics like piperacillin-tazobactam can include nephrotoxicity, which is a risk factor for renal failure (odds ratio 1.7) 7

Algorithm for Assessment of Bacterial Infection Likelihood

1. Obtain appropriate cultures before starting antibiotics 4
2. Measure procalcitonin levels for patients with suspected respiratory infections 4
3. Perform appropriate imaging based on suspected source of infection 4
4. Assess severity of illness:
   • For septic shock or bacterial meningitis: Administer broad-spectrum antibiotics immediately 5
   • For less severe presentations: Consider watchful waiting with close monitoring 4, 5
5. Re-evaluate within 24-48 hours based on culture results and clinical response 4
6. De-escalate to targeted therapy as soon as possible based on culture results 4, 3