What is the initial treatment and diagnostic approach for a patient presenting with community-acquired pneumonia (CAP), considering factors such as severity of symptoms, age, and underlying medical conditions?

Treatment and Diagnostic Approach for Community-Acquired Pneumonia

Initial Diagnostic Testing

For outpatients with suspected CAP, chest radiography and extensive diagnostic testing are not necessary in the majority of cases. 1

Outpatient Diagnostics

• Pulse oximetry should be performed in emergency and urgent care settings for simple oxygenation assessment 1
• Chest radiography is reserved for patients with severe symptoms, those requiring hospitalization, or when diagnosis is uncertain 1
• Testing for COVID-19 and influenza should be performed when these viruses are circulating in the community, as results may affect treatment decisions and infection prevention strategies 2

Inpatient Diagnostics

All hospitalized patients require the following investigations on admission: 1

• Chest radiograph (posteroanterior and lateral views) 1
• Complete blood count with differential 1
• Comprehensive metabolic panel (urea, electrolytes, liver function tests) 1
• C-reactive protein 1
• Oxygenation assessment (pulse oximetry or arterial blood gas) 1
• Blood cultures (two sets from separate sites before antibiotic administration) 3
• Sputum Gram stain and culture (if productive cough present) 3
• Urinary antigen testing for Legionella pneumophila serogroup 1 in severe CAP or ICU patients 3

Severity Assessment and Site-of-Care Decision

Use the CURB-65 score to guide initial site-of-care decisions, supplemented by clinical judgment regarding ability to take oral medications and availability of support resources. 1

CURB-65 Scoring System

Each criterion scores 1 point: 1

• Confusion (new onset)
• Urea >7 mmol/L (BUN >19 mg/dL)
• Respiratory rate ≥30 breaths/minute
• Blood pressure (systolic <90 mmHg or diastolic ≤60 mmHg)
• Age ≥65 years

Site-of-Care Recommendations

• CURB-65 score 0-1: Outpatient treatment appropriate 1
• CURB-65 score ≥2: Consider hospitalization or intensive in-home health care services 1
• ICU admission criteria: Presence of severe sepsis/septic shock, need for mechanical ventilation, or ≥3 minor criteria (respiratory rate ≥30/min, PaO₂/FiO₂ ratio ≤250, multilobar infiltrates, confusion, uremia, leukopenia, thrombocytopenia, hypothermia, hypotension requiring aggressive fluid resuscitation) 4

Empiric Antibiotic Treatment

Outpatient Treatment: Healthy Adults Without Comorbidities

Amoxicillin 1 g orally three times daily for 5-7 days is the preferred first-line therapy for previously healthy outpatients with CAP. 3

• Alternative: Doxycycline 100 mg orally twice daily for 5-7 days 3
• Macrolides (azithromycin 500 mg day 1, then 250 mg daily for days 2-5; or clarithromycin 500 mg twice daily) should only be used when local pneumococcal macrolide resistance is documented to be <25% 3

Outpatient Treatment: Adults With Comorbidities

For patients with comorbidities (COPD, diabetes, chronic heart/liver/renal disease, malignancy, or antibiotic use within past 3 months), use combination therapy or respiratory fluoroquinolone monotherapy. 3

Preferred combination regimen: 3

• Amoxicillin-clavulanate 875 mg/125 mg orally twice daily PLUS
• Azithromycin 500 mg orally day 1, then 250 mg daily days 2-5 (or clarithromycin 500 mg twice daily)
• Duration: 5-7 days total

Alternative monotherapy: 3

• Levofloxacin 750 mg orally daily for 5 days OR
• Moxifloxacin 400 mg orally daily for 5 days

Inpatient Treatment: Non-ICU Hospitalized Patients

Administer the first antibiotic dose immediately in the emergency department—delayed administration beyond 8 hours increases 30-day mortality by 20-30%. 3

Two equally effective regimens exist with strong evidence: 3

Regimen 1 (β-lactam plus macrolide): 3

• Ceftriaxone 1-2 g IV daily PLUS
• Azithromycin 500 mg IV or oral daily
• Duration: Minimum 5 days and until afebrile for 48-72 hours with ≤1 sign of clinical instability

Regimen 2 (respiratory fluoroquinolone monotherapy): 3

• Levofloxacin 750 mg IV daily OR
• Moxifloxacin 400 mg IV daily
• Duration: Minimum 5 days and until afebrile for 48-72 hours with ≤1 sign of clinical instability

For penicillin-allergic patients: Use respiratory fluoroquinolone monotherapy 3

Inpatient Treatment: ICU-Level Severe CAP

Combination therapy is mandatory for all ICU patients—monotherapy is inadequate for severe disease. 3

Preferred regimen: 3

• Ceftriaxone 2 g IV daily (or cefotaxime 1-2 g IV every 8 hours or ampicillin-sulbactam 3 g IV every 6 hours) PLUS
• Azithromycin 500 mg IV daily OR respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily)
• Duration: 10-14 days for severe disease

Adjunctive therapy considerations: 4

• Systemic corticosteroids within 24 hours of severe CAP development may reduce 28-day mortality 2
• Screen hypotensive, fluid-resuscitated patients for occult adrenal insufficiency 4
• Consider noninvasive ventilation for patients with hypoxemia or respiratory distress unless severe hypoxemia (PaO₂/FiO₂ ratio <150) and bilateral infiltrates require immediate intubation 4

Special Populations Requiring Broader Coverage

Add antipseudomonal coverage when the following risk factors are present: 3

• Structural lung disease (bronchiectasis, cystic fibrosis)
• Recent hospitalization with IV antibiotics within 90 days
• Prior respiratory isolation of P. aeruginosa
• Recent broad-spectrum antibiotic use

Antipseudomonal regimen: 3

• Antipseudomonal β-lactam (piperacillin-tazobactam 4.5 g IV every 6 hours, cefepime 2 g IV every 8 hours, imipenem 500 mg IV every 6 hours, or meropenem 1 g IV every 8 hours) PLUS
• Ciprofloxacin 400 mg IV every 8 hours OR levofloxacin 750 mg IV daily PLUS
• Aminoglycoside (gentamicin or tobramycin 5-7 mg/kg IV daily) plus azithromycin

Add MRSA coverage when the following risk factors are present: 3

• Prior MRSA infection or colonization
• Recent hospitalization with IV antibiotics
• Post-influenza pneumonia
• Cavitary infiltrates on imaging

MRSA regimen addition: 3

• Vancomycin 15 mg/kg IV every 8-12 hours (target trough 15-20 mg/mL) OR
• Linezolid 600 mg IV every 12 hours

Transition from IV to Oral Therapy

Switch from IV to oral antibiotics when the patient meets all clinical stability criteria: 3

Clinical Stability Criteria 3

• Hemodynamically stable (no vasopressor requirement)
• Clinically improving (reduced cough and dyspnea)
• Afebrile for 48-72 hours
• Decreasing white blood cell count
• Able to take oral medications
• Normal gastrointestinal function with adequate oral intake

Typical transition occurs by hospital day 2-3. 3

Oral Step-Down Regimens 3

• From ceftriaxone plus azithromycin: Amoxicillin 1 g orally three times daily plus azithromycin 500 mg orally daily (complete 5-7 day total course)
• From respiratory fluoroquinolone IV: Continue same fluoroquinolone orally at same dose

Duration of Antibiotic Therapy

Treat for a minimum of 5 days and until the patient is afebrile for 48-72 hours with no more than one sign of clinical instability. 3

Standard Duration 3

• Uncomplicated CAP: 5-7 days total (including IV days)
• Severe CAP (ICU): 10-14 days
• Specific pathogens requiring extended therapy (14-21 days): 3
  • Legionella pneumophila
  • Staphylococcus aureus
  • Gram-negative enteric bacilli

Treatment duration should generally not exceed 8 days in a responding patient without specific indications, as longer courses increase antimicrobial resistance risk without improving outcomes. 3

Follow-Up and Monitoring

Outpatient Follow-Up 3

• Clinical review at 48 hours or sooner if clinically indicated
• Scheduled clinical review at 6 weeks for all patients
• Chest radiograph at 6 weeks reserved for patients with persistent symptoms, physical signs, or high risk for underlying malignancy (smokers, age >50 years)

Inpatient Monitoring 3

• Assess clinical response at days 2-3, including fever resolution and lack of progression of pulmonary infiltrates
• If no clinical improvement by day 2-3, obtain repeat chest radiograph, CRP, white cell count, and additional microbiological specimens
• Chest radiograph need not be repeated prior to hospital discharge in patients with satisfactory clinical recovery

Critical Pitfalls to Avoid

Never use macrolide monotherapy in areas where pneumococcal macrolide resistance exceeds 25%—this leads to treatment failure. 3

Never delay antibiotic administration beyond 8 hours in hospitalized patients—this increases 30-day mortality by 20-30%. 3

Never use macrolide monotherapy for hospitalized patients—this provides inadequate coverage for typical bacterial pathogens like S. pneumoniae. 3

Avoid indiscriminate fluoroquinolone use in uncomplicated outpatient CAP due to FDA warnings about serious adverse events and resistance concerns. 3

Do not automatically escalate to broad-spectrum antibiotics based solely on immunosuppression or comorbidities without documented risk factors for resistant organisms. 3

Obtain blood and sputum cultures before initiating antibiotics in all hospitalized patients to allow pathogen-directed therapy and de-escalation. 3

Prevention Strategies

Vaccination status should be assessed at hospital admission for all patients. 4

Pneumococcal Vaccination 4

• Pneumococcal polysaccharide vaccine recommended for persons ≥65 years and those with selected high-risk concurrent diseases
• May be administered at hospital discharge or during outpatient treatment

Influenza Vaccination 4

• Annual influenza vaccination recommended for all patients, especially those with medical illnesses and healthcare workers
• Should be offered at hospital discharge or during outpatient treatment during fall and winter

Smoking Cessation 4

• Smoking cessation should be a goal for all patients hospitalized with CAP who smoke
• Smokers who will not quit should be vaccinated for both pneumococcus and influenza