Schematic Diagram of Community Acquired Pneumonia Diagnosis and Treatment Pathways

community acquired pneumonia schematic diagram

Begin with a structured flowchart dividing cases by symptom severity: mild (cough, low fever, fatigue), moderate (dyspnea, chest pain, fever >38°C), and severe (respiratory failure, hypotension, altered mental status). Each branch must include mandatory diagnostic steps–pulse oximetry for all, chest X-ray immediately for moderate/severe cases, and CRP/procalcitonin for suspected bacterial etiology. Omit broad-spectrum antibiotics if viral markers dominate unless clinical deterioration occurs within 48 hours.

For suspected bacterial causes, prioritize sputum Gram stain and culture in patients producing purulent sputum. If unable to expectorate, perform nasopharyngeal swabs for atypicals (Mycoplasma pneumoniae, Chlamydia pneumoniae) in outbreaks. In hospitalized patients, add blood cultures if infiltrates suggest lobar consolidation or pleural effusion. Time-to-result targets: <6 hours for Gram stain, <48 hours for cultures–delayed reporting increases mortality by 12% per day.

Categorize imaging findings using a three-tiered system:

1. Patchy opacity (bronchopneumonia, often viral/atypical),

2. Lobar consolidation (classic bacterial, e.g., Streptococcus pneumoniae),

3. Interstitial changes (PCP in immunocompromised, viral). Layer microbiological data onto this framework–PCR for influenza/COVID-19 if seasonal prevalence exceeds 15%.

In resource-limited settings, replace CRP with leukocyte count trends: rising bands (≥10%) or left shift >12% strongly correlate with bacterial infection. For empiric therapy, start with amoxicillin-clavulanate (1g IV q8h) for outpatient management; escalate to ceftriaxone (2g IV q24h) + azithromycin (500mg IV q24h) if ICU admission is required. Modify within 72 hours based on microbiology–persistent fever beyond this window indicates disease progression or resistant pathogen.

Discharge criteria must integrate both clinical stability (respiratory rate <24, SpO₂ ≥90%, no hypotension) and lab resolution (CRP decline ≥50% from peak). Arrange follow-up chest X-ray at 4–6 weeks for smokers, elderly, or patients with initial extensive infiltrates to exclude underlying malignancy or structural lung disease.

Visual Framework for Locally Originated Lung Infections

Begin with a structured flow depicting key phases: exposure, pathogenesis, clinical presentation, diagnostic steps, and management pathways. Place the infectious agent at the leftmost point, branching into viral, bacterial, and atypical causes (e.g., Streptococcus pneumoniae (30-50% of cases), Mycoplasma pneumoniae (10-20%), Haemophilus influenzae (5-10%), and respiratory viruses (15-30%)). Use colour-coding: red for bacterial, blue for viral, and green for atypical.

Detail host risk factors as layered boxes beneath each pathogen branch. Include age >65 (OR 1.5), chronic heart/lung disease (OR 2.0), immunosuppression (OR 2.5), smoking (OR 1.8), and recent hospitalisation (OR 1.3). Link these directly to mortality rates: 5% for low-risk, 15% for moderate-risk, and >30% for high-risk groups (CURB-65 score ≥3).

Outline subsequent stages as cascading arrows. First, alveolar consolidation–show progression via chest X-ray patterns: lobar, interstitial, or bronchopneumonic. Label typical findings: air bronchograms, pleural effusions, or cavitation. Connect each imaging pattern to empirical antibiotic classes: β-lactams for lobar, macrolides for interstitial, and fluoroquinolones for cavitary disease. Specify dosages: amoxicillin 1 g TDS, azithromycin 500 mg OD ×5 days, or levofloxacin 750 mg OD ×5 days.

Incorporate microbiological diagnostics as decision nodes. Add sputum Gram stain and culture (sensitivity 60%, specificity 90% if >25 polymorphs/lpf), urinary antigen for S. pneumoniae and Legionella (sensitivity 70-90%), and PCR for respiratory viruses (turnaround 6-24 h). Highlight cost-effectiveness: urinary antigen test £20 versus sputum culture £50; prioritise antigen testing in CURB-65 score ≥2.

Visualise treatment pathways as diverging tracks. For outpatient management (CURB-65 0-1), use a single arrow leading to oral antibiotics and follow-up in 48-72 h. For inpatient care (CURB-65 ≥2), split into non-severe (ward-based) and severe (ICU) tracks. ICU track should include invasive ventilation rates (20%), vasopressor requirement (35%), and adjunctive corticosteroids (prednisolone 20 mg BD for 7 days, reducing mortality by 3%).

Conclude with complication nodes: parapneumonic effusion (20% of cases), empyema (5%), lung abscess (2%), and sepsis (10%). Link each to escalation protocols, e.g., drainage for effusion >2 cm on ultrasound, or thoracentesis with pH 90% on room air, and able to tolerate oral intake.

Core Elements of Lower Respiratory Infection Pathogenesis Mapping

Begin the flowchart with microbial entry points, distinguishing between inhalation (e.g., Streptococcus pneumoniae droplets) and aspiration (oropharyngeal flora translocation). Classify pathogens by prevalence: bacteria (70-80%), viruses (15-30%), atypicals (Mycoplasma, Chlamydia, Legionella). Include sub-branches for risk modifiers: immunocompromised states (HIV, chemotherapy) and chronic lung conditions (COPD, bronchiectasis).

Branch into host immune response with dual pathways: innate (macrophage activation, cytokine release) and adaptive (T-cell recruitment, antibody production). List key mediators:

  • Pro-inflammatory cytokines (IL-1β, TNF-α, IL-6)
  • Chemokines (CXCL8, CCL2)
  • Alveolar macrophage phagocytosis thresholds (after 105–106 CFU/mL)

Integrate lung tissue damage patterns using radiologic correlates:

  1. Lobar consolidation (S. pneumoniae, Klebsiella) – homogeneous opacity with air bronchograms
  2. Bronchopneumonia (Staphylococcus, Haemophilus) – patchy infiltrates along bronchi
  3. Interstitial (viral, Pneumocystis jirovecii) – reticular or ground-glass opacities

Critical Modifying Factors

Add conditional branches for comorbidity interactions. For diabetes, include:

  • Hyperglycemia-induced neutrophil dysfunction
  • Reduced mucociliary clearance (HbA1c >9%)
  • 4-fold increased risk of Staphylococcus aureus infection

Incorporate pharmacokinetics of antimicrobials as a parallel track. Highlight:

  • β-lactam penetration (amoxicillin reaches 30-50% serum levels in epithelial lining fluid)
  • Macrolide accumulation in alveolar macrophages (azithromycin 100x serum concentration)
  • Drug-drug interactions (e.g., quinolones + corticosteroids ↑ QT interval)

Complication Cascade

Design a terminal branch for disease progression endpoints:

  1. Parapneumonic effusion (pH
  2. Empyema (polymorphonuclear leukocytes >50,000/μL)
  3. Sepsis (SOFA score ≥2, lactate >2 mmol/L)
  4. Respiratory failure (PaO₂/FiO₂

Embed vaccine-preventable pathways. Show how:

  • 23-valent pneumococcal vaccine reduces bacteremia risk by 75%
  • Influenza vaccine lowers secondary infection odds (OR 0.52)
  • PCV13 serotypes now account for

Include a treatment response decision node based on 48-hour benchmarks: fever resolution, oxygen saturation improvement (>2% Δ), CRP reduction (>30% decrease). For non-responders, branch to alternative interventions:

  • CT chest (eliminate abscess/empyema)
  • Bronchoalveolar lavage (exclude fungal/TB)
  • Surgical consultation (lung abscess >6 cm)

Step-by-Step Diagnosis Pathway in Visual Flow

Begin with clinical evaluation. Assess vital signs–temperature >38°C, respiratory rate >20/min, heart rate >100 bpm, and oxygen saturation

Order chest X-ray (CXR) as the primary imaging tool. Look for focal infiltrates, lobar consolidation, or interstitial patterns. Lobar consolidation suggests typical bacterial pathogens (e.g., Streptococcus pneumoniae); patchy or bilateral infiltrates may indicate atypical agents (e.g., Mycoplasma pneumoniae) or viral causes. If CXR is equivocal but clinical suspicion remains high, proceed to computed tomography (CT) for detailed lung parenchyma assessment.

Collect sputum Gram stain and culture within the first hour of admission if the patient can produce purulent sputum. Target >25 polymorphonuclear cells and urinary antigen tests for Legionella pneumophila serogroup 1 and S. pneumoniae, which provide rapid results (

For moderate-to-severe cases, perform pulse oximetry and arterial blood gas (ABG) analysis if SpO₂ ≤90% or respiratory distress is evident. Calculate CURB-65 score–confusion, urea >7 mmol/L, respiratory rate ≥30/min, blood pressure lactate measurement and blood cultures within 1 hour of presentation.

Use polymerase chain reaction (PCR) panels for viral detection (e.g., influenza, SARS-CoV-2, RSV) in high-risk groups or during outbreaks. For immunocompromised patients, add serology for fungal agents (e.g., Histoplasma, Coccidioides) or bronchoalveolar lavage (BAL) if initial diagnostics are inconclusive. BAL is indicated when sputum is unobtainable or in non-resolving cases after 72 hours of empiric therapy.

Empiric Antibiotic Selection Based on Risk

For outpatient management (CURB-65 0–1): prescribe amoxicillin 1 g TID or doxycycline 100 mg BID for 5–7 days. Add a macrolide (e.g., azithromycin 500 mg day 1, then 250 mg daily) if atypical coverage is needed. For hospitalized patients (CURB-65 2–3): combine ceftriaxone 1–2 g IV daily or ampicillin-sulbactam 1.5–3 g IV q6h with a macrolide. ICU cases (CURB-65 4–5) require vancomycin (15 mg/kg IV q12h) or linezolid 600 mg IV q12h plus piperacillin-tazobactam 4.5 g IV q6h for Pseudomonas coverage.

Reassess at 48–72 hours. If no improvement, switch to broader-spectrum agents (e.g., carbapenems) or escalate diagnostics. Discontinue antibiotics if an alternative diagnosis (e.g., pulmonary edema, malignancy) is confirmed. For viral causes, initiate oseltamivir 75 mg BID within 48 hours of symptom onset if influenza is detected. Document all steps in the patient record with timestamps for audit trails.