What is the evaluation and management approach for a patient presenting to the emergency department with fever?

Evaluation of Fever in the Emergency Department

Initial Assessment and Temperature Measurement

For accurate fever detection in the ED, use rectal temperature (most accurate, closest to core temperature) in neonates and young children, or oral temperature in cooperative older patients and adults, avoiding less reliable methods like axillary, tympanic, or temporal artery measurements. 1 In critically ill patients with invasive monitoring already in place, central temperature monitoring via pulmonary artery catheter thermistors, bladder catheters, or esophageal balloon thermistors is preferred. 1

• Fever is defined as temperature ≥38.0°C (100.4°F). 1
• Oral temperatures have poor sensitivity for detecting fever; if clinical suspicion exists despite normal oral reading, obtain core temperature measurement. 2
• Critical pitfall: Fever may be absent in elderly and immunocompromised patients despite serious infection. 2
• Antipyretic use within 4 hours may mask fever at presentation. 1

Age-Stratified Evaluation Approach

Neonates and Infants (≤90 days)

All febrile infants aged 29-90 days require lumbar puncture, as no adequate predictors exist to safely exclude bacterial meningitis. 3

• Infants <28 days: Highest risk group requiring full sepsis workup including blood culture, urine culture, lumbar puncture, and chest radiograph. 1, 3
• Infants 29-90 days: Obtain complete blood count, blood culture, urinalysis with culture, and cerebrospinal fluid analysis. 1, 3
• Risk of serious bacterial infection: 13% in neonates (3-28 days), 9% in infants (29-56 days), 7% in infants ≤90 days. 1
• Most common pathogens: Escherichia coli (43.7%) and Group B Streptococcus; also consider Listeria monocytogenes. 3
• Empiric antibiotics must be initiated immediately after cultures if bacterial meningitis suspected, as 71% of bacterial meningitis cases have positive blood cultures. 3

Children (2 months to 2 years)

For well-appearing febrile children aged 2 months to 2 years, evaluate for urinary tract infection based on clinical predictors, obtain urine testing via catheterization or suprapubic aspiration (not bag collection), and perform chest radiograph only if specific respiratory findings present (tachypnea, hypoxia, rales, decreased breath sounds). 1

• Fever accounts for 15% of all pediatric ED visits. 1
• Majority have benign viral infections, but only 58% of those with bacteremia or bacterial meningitis appear clinically ill. 1
• Special consideration: If fever ≥5 days with rash and swollen hands, urgently evaluate for Kawasaki disease with immediate echocardiography, laboratory testing (CBC, ESR, CRP, comprehensive metabolic panel), and treatment with IVIG 2 g/kg plus high-dose aspirin if criteria met. 4

Adults

In adult febrile patients, perform chest radiograph as initial imaging, obtain blood cultures only if septic shock present or results will change management, and pursue CT imaging for post-surgical patients or those with abdominal/pelvic symptoms when initial workup non-diagnostic. 1

Specific Clinical Scenarios:

Febrile Neutropenia (absolute neutrophil count <1000/mm³):

• Obtain thorough history, physical examination, chest radiograph, urinalysis, blood cultures, and urine culture. 5
• ED evaluation identifies 81% of infection sources; all focal infections are diagnosed in ED. 5
• Empiric therapy: Cefepime 2 g IV every 8 hours for 7 days or until neutropenia resolves. 6
• High-risk patients (recent bone marrow transplant, hypotension, hematologic malignancy, severe/prolonged neutropenia) may require combination therapy rather than monotherapy. 6

Post-Surgical Fever:

• Perform CT scan in collaboration with surgical service if etiology not identified by initial workup (chest radiograph, physical examination, basic labs). 1
• For abdominal/pelvic surgery patients with fever and abdominal symptoms or abnormal liver function tests, obtain formal bedside diagnostic ultrasound. 1
• Avoid routine abdominal ultrasound in patients without abdominal signs, symptoms, or liver function abnormalities. 1

Fever Without Source:

• If chest radiograph abnormal, perform thoracic bedside ultrasound when expertise available to identify pleural effusions and parenchymal pathology. 1
• If other diagnostic tests fail to establish etiology and transport risk acceptable, consider ¹⁸F-fluorodeoxyglucose PET/CT. 1
• For patients with central venous catheters, obtain simultaneous central and peripheral blood cultures. 1

Laboratory and Imaging Considerations

Temperature >39.5°C is associated with significantly worse outcomes and warrants aggressive evaluation and treatment. 7

• Temperature >39.7°C progressively associated with increased mortality (OR 1.64-2.22) and AKI (OR 1.48-2.91) compared to 38.0-38.1°C. 7
• Temperature >39.9°C independently associated with increased mortality and AKI in multivariate analysis. 7
• C-reactive protein, erythrocyte sedimentation rate, and procalcitonin lack sufficient sensitivity and specificity to definitively rule in bacterial infection. 2

Antipyretic Management

Avoid routine antipyretic use solely for temperature reduction in critically ill patients; reserve for patient comfort. 1

• If antipyretics used for comfort, prefer pharmacologic agents over nonpharmacologic cooling methods. 1
• For bacterial fever in ED, paracetamol/ibuprofen 500/150 mg combination more effective than paracetamol 1000 mg alone at 1 hour (48.6% vs 33.6% response rate). 8
• Both regimens equally effective at 2 hours for all fever etiologies (90.5% vs 91.9%). 8

Differential Diagnosis Framework

Maintain broad differential including both infectious and non-infectious causes based on clinical context. 2, 9

Infectious Causes by System:

• Respiratory: Pneumonia (S. pneumoniae, P. aeruginosa, K. pneumoniae, Enterobacter) 6
• Urinary: UTI/pyelonephritis (E. coli, K. pneumoniae, P. mirabilis) 6
• Skin/Soft Tissue: Cellulitis, abscess (S. aureus, S. pyogenes) 6
• Intra-abdominal: Complicated infections (E. coli, viridans streptococci, P. aeruginosa, B. fragilis) 6
• Bloodstream: Bacteremia, sepsis 3, 5
• CNS: Meningitis (especially infants <90 days) 3

Non-Infectious Causes:

• Neoplastic/inflammatory conditions 8
• Drug fever 9
• Thromboembolic disease 9
• Endocrine disorders 9

COVID-19 Considerations

For patients with fever plus respiratory symptoms (cough, dyspnea) or relevant exposure history, perform RT-PCR nasopharyngeal swab and baseline chest imaging (CT preferred, chest X-ray or lung ultrasound if CT unavailable). 1

• Suspect COVID-19 if: fever with respiratory symptoms and travel/residence in area with local transmission within 14 days, OR acute respiratory illness with confirmed COVID-19 contact within 14 days, OR severe respiratory infection requiring hospitalization without alternative explanation. 1
• Characteristic labs: Leucopenia, lymphopenia, elevated AST, elevated inflammatory markers (CRP, ESR), elevated LDH, elevated D-dimer and fibrinogen. 1