What is the best approach to diagnose and manage a patient with a potential infection?

Diagnostic and Management Approach for Suspected Infection

Begin with a detailed patient history focusing on infection source, followed by systematic physical examination targeting likely sites, obtain cultures before antibiotics when feasible, and initiate empirical antimicrobial therapy within 1 hour while awaiting results. 1

Initial Clinical Assessment

History Collection

• Document timing and character of symptoms including fever onset, pain location and severity, respiratory symptoms, gastrointestinal complaints, and urinary symptoms 1
• Identify potential infection sources through systematic review: recent procedures, indwelling devices (catheters, lines), travel history, sick contacts, and immunosuppression status 1
• Assess risk factors including HIV/AIDS status, diabetes, malignancy, immunosuppressive medications, recent antibiotic use, and healthcare exposures 1
• In resource-limited settings, specifically inquire about malaria exposure, tuberculosis contacts, and over-the-counter antibiotic self-medication 1

Physical Examination Priorities

Perform a systematic head-to-toe examination targeting infection sources rather than a cursory general assessment 1:

• Vital signs: Temperature, heart rate, blood pressure, respiratory rate, and oxygen saturation 1
• Skin and soft tissue: Examine for cellulitis, abscesses, surgical site infections, rashes (including dermatomal patterns), and signs of endocarditis (splinter hemorrhages, Osler nodes) 1
• Head and neck: Inspect oropharynx for thrush or gingivitis, palpate for lymphadenopathy, assess for meningismus 1
• Cardiovascular: Auscultate for new murmurs suggesting endocarditis 1
• Pulmonary: Assess for consolidation, crackles, or decreased breath sounds 1
• Abdominal: Palpate for peritoneal signs, organomegaly, right upper quadrant tenderness, and assess for ascites 1
• Genitourinary: Examine for costovertebral angle tenderness, suprapubic tenderness, and vaginal/urethral discharge 1
• Neurological: Assess mental status changes and focal deficits 1

The history leads to diagnosis in 76% of cases, with physical examination contributing an additional 12%, making these steps critical before laboratory testing 2.

Laboratory and Microbiological Diagnosis

Specimen Collection Strategy

Obtain cultures before initiating antibiotics whenever clinically safe and feasible 1:

• Blood cultures: Collect 2-3 sets with 20 mL per set in adults to maximize diagnostic yield 1
• Site-specific sampling: Obtain fluid or tissue from the suspected infection source (urine, sputum, wound drainage, cerebrospinal fluid, joint aspirate) using sterile technique 1
• Timing is critical: Sample before antibiotics when possible, but never delay antimicrobial therapy beyond 1 hour in sepsis to obtain cultures 1

Microbiological Processing

• Gram stain and microscopy: Perform immediately on all appropriate specimens for rapid preliminary identification 1
• Culture and susceptibility testing: Process all samples for bacterial culture with antibiotic susceptibility testing to guide targeted therapy 1
• Special testing: In endemic areas or based on clinical suspicion, perform thick smear for malaria, fungal cultures, or specific serologies 1

Baseline Laboratory Tests

Order the following at diagnosis 1:

• Complete blood count with differential (neutrophil and lymphocyte counts)
• C-reactive protein
• Creatinine and liver function tests
• Urinalysis if urinary symptoms or prior UTI history
• HIV serology after counseling
• Hepatitis B and C serologies
• Varicella zoster virus serology if no reliable vaccination history

Imaging Studies

When to Image

• Skip imaging if diffuse peritonitis is present and immediate surgery is planned 1
• CT with IV contrast is the preferred modality for suspected intra-abdominal infection in stable patients not requiring immediate laparotomy 1
• Chest imaging: Obtain chest X-ray for suspected pneumonia or tuberculosis; use portable equipment for critically ill patients to minimize transport 1
• In neutropenic patients with persistent fever or right upper quadrant pain, obtain imaging to exclude chronic disseminated candidiasis 1

Antimicrobial Therapy Initiation

Timing

Administer antibiotics within 1 hour of recognizing sepsis or septic shock 1:

• For septic shock: Give antibiotics immediately upon diagnosis 1
• For severe sepsis without shock: Start in the emergency department 1
• Ensure adequate drug levels during any source control procedure 1

Empirical Regimen Selection

Tailor empirical therapy to local pathogen patterns, resistance profiles, and patient-specific factors 1:

• Dosing: Use maximum recommended doses initially given the high mortality risk; this is especially important if drug quality is uncertain 1
• Route: Prefer intravenous administration for optimal bioavailability in acute phase 1
• Local considerations: Adjust for regional antimicrobial resistance patterns, HIV/AIDS prevalence, and endemic infections 1
• In children with community-acquired severe pneumonia (ages 2-59 months) in resource-limited settings, chloramphenicol was superior to ampicillin plus gentamicin 1

Subsequent Adjustments

• De-escalate based on culture results and susceptibility testing once available 1
• Adjust doses for renal or hepatic dysfunction after the acute phase 1
• Transition to oral therapy when the patient improves and intestinal absorption is maintained 1

Resuscitation and Supportive Care

Fluid Management

In patients with tissue hypoperfusion, infuse fluids aggressively 1:

• Target systolic blood pressure ≥90 mmHg in adults
• Continue liberal infusions for 24-48 hours; >4 L may be required in the first 24 hours
• Use crystalloids or colloids (colloids preferred for severe Dengue shock syndrome in children) 1

Vasopressor Support

• Use dopamine or epinephrine for persistent hypoperfusion despite adequate fluid resuscitation 1
• Monitor blood pressure and heart rate frequently in patients requiring vasopressors 1
• Add hydrocortisone (up to 300 mg/day) or prednisolone (up to 75 mg/day) in adults requiring escalating vasopressor doses 1

Oxygen and Ventilation

• Target oxygen saturation >90% using pulse oximetry 1
• Position patients semi-recumbent (head of bed 30-45°) to reduce aspiration risk 1
• Consider non-invasive ventilation for dyspnea or persistent hypoxemia despite oxygen therapy if staff is trained 1

Source Control

Drain or debride infection sources as soon as basic resuscitation and antibiotics are initiated 1:

• Remove infected foreign bodies or devices 1
• Time source control based on clinical urgency, balancing immediate intervention against patient stabilization 1
• For intra-abdominal infections, source control is essential alongside antimicrobial therapy 1

Common Pitfalls to Avoid

• Do not delay antibiotics to obtain cultures in septic patients—cultures are important but secondary to immediate antimicrobial therapy 1
• Do not assume blood cultures alone are sufficient—obtain site-specific specimens as blood cultures may be negative in localized infections 1
• Do not use inadequate antibiotic doses—maximum recommended doses are required initially in sepsis 1
• Do not forget to adjust empirical therapy to local resistance patterns and endemic diseases, particularly in resource-limited settings 1
• Do not overlook source control—antibiotics alone are insufficient without drainage or debridement of infected foci 1