What is the initial approach to managing a patient with an infectious disease?

Initial Approach to Managing a Patient with Infectious Disease

The initial management of a patient with suspected infectious disease must prioritize immediate assessment of disease severity, rapid diagnostic evaluation, and emergent empiric antimicrobial therapy without delay, even before completing the full diagnostic workup. 1, 2

Immediate Clinical Assessment and Severity Stratification

Upon encountering a patient with suspected infectious disease, immediately assess for life-threatening presentations:

• Evaluate for acute bacterial meningitis by checking for fever, headache, neck stiffness, and altered mental status; if suspected, obtain blood cultures and initiate empiric antimicrobials (ceftriaxone plus vancomycin, with ampicillin added for immunocompromised patients) immediately, even before lumbar puncture or CT imaging. 1, 2

• Assess respiratory status using pulse oximetry; patients with SaO2 <92% require arterial blood gas measurements and immediate oxygen therapy to maintain PaO2 >8 kPa and SaO2 >92%. 1, 3

• Screen for sepsis and shock by measuring blood pressure, heart rate, and mental status; hypotension with systolic BP <100 mmHg or metabolic acidosis with bicarbonate <18 mmol/L indicates severe illness requiring immediate intervention. 1

• Obtain chest radiograph and ECG for all patients with abnormal cardiorespiratory symptoms to identify pneumonia, cardiac complications, or other organ involvement. 1, 3

Diagnostic Workup (Without Delaying Treatment)

Critical principle: Never delay antimicrobial therapy while awaiting diagnostic studies, as mortality increases with each hour of delay. 1, 2

Essential Initial Investigations:

• Blood cultures should be obtained before antibiotic administration whenever possible, but antibiotics must not be delayed if venous access is difficult. 1

• For severe pneumonia (CURB-65 score 3-5): Obtain blood cultures, pneumococcal urine antigen, sputum Gram stain and culture (if purulent sample available and no prior antibiotics given), and consider paired serology. 1

• For suspected meningitis: Perform lumbar puncture immediately unless contraindicated (signs of increased intracranial pressure, coagulopathy, or hemodynamic instability); if LP is delayed, give antibiotics first and perform LP later. 1, 2

• HIV testing should be considered in all patients with suspected serious infections, particularly those with oral thrush, severe lymphopenia, or atypical presentations. 2, 4

Empiric Antimicrobial Therapy

Initiate antimicrobials within the first hour of presentation for severe infections; the first dose should be administered while still in the emergency department. 1, 2, 3

Treatment Selection Based on Clinical Syndrome:

• Suspected bacterial meningitis: Ceftriaxone 2g IV plus vancomycin 15-20 mg/kg IV; add ampicillin 2g IV every 4 hours if age >50 years or immunocompromised (to cover Listeria). 1, 2

• Severe community-acquired pneumonia: β-lactam (ceftriaxone, cefotaxime, or ampicillin-sulbactam) plus either azithromycin or a respiratory fluoroquinolone. 3

• Suspected cerebritis: Third-generation cephalosporin plus metronidazole plus aciclovir (to cover HSV encephalitis); adjust aciclovir dose in renal impairment. 4

• Influenza-like illness during pandemic: Consider oseltamivir 75 mg twice daily for 5 days if initiated within 48 hours of symptom onset. 5

Respiratory Support and Monitoring

• Provide high-concentration oxygen (35% or greater) for patients with PaO2 <8 kPa, unless pre-existing COPD with CO2 retention is present. 1

• For COPD patients: Start with low oxygen concentrations (24-28%) and titrate based on repeated arterial blood gas measurements, aiming for SaO2 >90% without causing pH to fall below 7.35. 1

• Monitor vital signs at least twice daily: Temperature, respiratory rate, pulse, blood pressure, mental status, oxygen saturation, and inspired oxygen concentration; use an Early Warning Score system for convenience. 1, 3

Infection Control Measures

Apply standard precautions immediately and upgrade to airborne precautions whenever highly infectious disease is suspected, as modes of transmission are often underestimated. 1

• Place patients with suspected highly infectious diseases in single isolation rooms with negative pressure if available. 1

• Healthcare workers should wear appropriate personal protective equipment before patient contact. 1

• Minimize aerosol-generating procedures; if intubation is required, use rapid sequence induction by the most skilled person available wearing full PPE. 1

Critical Pitfalls to Avoid

• Never assume viral meningitis based on low CSF cell count alone in immunocompromised patients, as bacterial meningitis can present with minimal pleocytosis. 2

• Do not rely on negative CSF cultures to rule out bacterial meningitis if antibiotics were given before lumbar puncture, as CSF can be sterilized within 2-4 hours. 2

• Do not ignore oral thrush in adults, as this mandates HIV testing and consideration of disseminated fungal infection. 2

• Avoid delaying antimicrobial therapy for diagnostic imaging; if CT scan is needed before lumbar puncture, give antibiotics first. 1, 2

• Do not omit ampicillin in patients with suspected immunocompromise, as Listeria carries high mortality if untreated. 2

Supportive Care

• Assess for volume depletion and provide intravenous fluids as needed. 1, 3

• Consider thromboprophylaxis with low molecular weight heparin (e.g., enoxaparin 40 mg subcutaneously) for patients with acute respiratory failure. 3

• Provide nutritional support in severe or prolonged illness. 1, 3

• Assess for cardiac complications including myocardial dysfunction, which commonly accompanies severe infections. 1