1..Pneumonia. Definition, etiopathogenesis, classification. Community-acquired pneumonia: clinic, diagnostic criteria. Choice of treatment site (CRB-65 scale). The principle of choosing antibiotic therapy, assessing its effectiveness in a polyclinic.
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Pneumonia: Comprehensive Overview
1. Definition
Pneumonia is an acute infection of the alveolar (gas-exchanging) parenchyma of the lung, characterized by inflammation and consolidation of the lung tissue. It involves filling of alveoli with inflammatory exudate, impairing gas exchange. The term encompasses infections caused by bacteria, viruses, fungi, or parasites.
Community-acquired pneumonia (CAP) is defined as an acute pulmonary infection occurring in a patient who is not hospitalized and not residing in a long-term care facility for ≥14 days before symptom onset.
Other acquisition-based definitions (per Tintinalli's Emergency Medicine):
| Type | Definition |
|---|---|
| Hospital-acquired pneumonia | New infection ≥48 h after hospital admission |
| Ventilator-acquired pneumonia | New infection ≥48 h after endotracheal intubation |
| Healthcare-associated pneumonia | Hospitalized ≥2 days in past 90 days; nursing home resident; home IV antibiotics; dialysis; chronic wound care; chemotherapy |
2. Etiopathogenesis
Mechanisms of Infection
Pathogenic organisms reach the lung by:
- Aspiration of oropharyngeal contents — most common route, especially in healthcare settings
- Inhalation of infectious droplets directly into the lower respiratory tract
- Hematogenous seeding — e.g., S. aureus, S. pneumoniae from bacteremia
Predisposing Factors
Aspiration risk: swallowing/esophageal disorders, stroke, nasogastric tube, intubation, seizure, syncope
Bacteremia risk: indwelling vascular/intrathoracic devices, debilitation
General: alcoholism, extremes of age, neoplasia, immunosuppression, chronic diseases (DM, renal failure, liver failure, CHF, COPD)
Bacteremia risk: indwelling vascular/intrathoracic devices, debilitation
General: alcoholism, extremes of age, neoplasia, immunosuppression, chronic diseases (DM, renal failure, liver failure, CHF, COPD)
Pathogenesis
Organisms induce an intense inflammatory response within alveoli → filling of air spaces with exudate and WBCs → impaired gas exchange. Organisms spread along the bronchial tree or through pores between adjacent alveoli (pores of Kohn). When consolidation involves an entire lobe, classic lobar pneumonia results, with characteristic air bronchograms on imaging. Interstitial infiltrates suggest viral or atypical pathogens.
Key Pathogens by Setting (Fishman's Pulmonary, Table 125-2)
| Setting | Common Pathogens |
|---|---|
| Outpatient, no comorbidities | S. pneumoniae, M. pneumoniae, C. pneumoniae, H. influenzae, respiratory viruses |
| Outpatient, with cardiopulmonary disease | All above + DRSP, enteric Gram-negatives, anaerobes (aspiration) |
| Inpatient, with comorbidities | S. pneumoniae (incl. DRSP), H. influenzae, M. pneumoniae, C. pneumoniae, enteric GNR (incl. P. aeruginosa), anaerobes, Legionella, viruses |
| Severe CAP, no Pseudomonas risk | S. pneumoniae, Legionella, H. influenzae, enteric GNR, S. aureus, M. pneumoniae |
| Severe CAP, Pseudomonas risk | All of the above + P. aeruginosa |
Risk factors for drug-resistant S. pneumoniae (DRSP): Age >65, β-lactam therapy in past 3 months, alcoholism, immunosuppression, multiple comorbidities, exposure to children in day care.
Risk factors for P. aeruginosa: Structural lung disease (bronchiectasis), corticosteroids >10 mg/day, broad-spectrum antibiotics >7 days in past month, malnutrition.
3. Classification
By Acquisition Setting
- Community-acquired (CAP)
- Hospital-acquired (HAP/nosocomial)
- Ventilator-associated (VAP)
- Healthcare-associated (HCAP)
By Radiographic/Anatomical Pattern
- Lobar pneumonia — consolidation of a whole lobe; air bronchograms; typically bacterial (S. pneumoniae, K. pneumoniae)
- Bronchopneumonia — patchy, multifocal infiltrates along bronchi; common with S. aureus, H. influenzae
- Interstitial pneumonia — diffuse interstitial infiltrates (reticulonodular); viruses, M. pneumoniae, P. jirovecii
By Clinical Syndrome
- Typical pneumonia: Sudden onset, high fever, rigors, productive cough, pleuritic chest pain, lobar consolidation on CXR → bacterial (esp. S. pneumoniae)
- Atypical pneumonia: Gradual onset, dry/nonproductive cough, headache, malaise, interstitial infiltrates → Mycoplasma, Chlamydophila, Legionella, viruses
By Severity (CAP-specific)
- Mild (outpatient)
- Moderate (inpatient, non-ICU)
- Severe (ICU-level care)
4. Community-Acquired Pneumonia: Clinical Features
Symptoms
- Typical: Abrupt onset of fever, rigors/chills, pleuritic chest pain, productive cough (rust-colored sputum in pneumococcal pneumonia), dyspnea
- Atypical: Gradual onset, dry cough, headache, myalgia, malaise, gastrointestinal symptoms (especially Legionella — diarrhea, nausea)
- In elderly: May present atypically — confusion/altered mental status, functional decline, without prominent respiratory complaints
Signs
- Fever (occasionally hypothermia in severe cases)
- Tachycardia, tachypnea
- Decreased breath sounds, dullness to percussion, bronchial breathing over consolidation
- Crackles (crepitations) on auscultation
- Cyanosis in severe cases
Organism-Specific Clues (Tintinalli's, Table 65-3)
| Organism | Clues |
|---|---|
| S. pneumoniae | Sudden onset, rust-colored sputum, lobar infiltrate |
| Klebsiella pneumoniae | Alcoholics, "currant jelly" sputum, upper lobe, bulging fissure |
| Legionella pneumophila | Diarrhea, hyponatremia, multi-organ involvement, no predominant organism on sputum Gram stain |
| Mycoplasma pneumoniae | Young patients, upper + lower respiratory symptoms, bullous myringitis, interstitial pattern |
| Chlamydophila pneumoniae | Gradual onset, wheezing, sinus symptoms; no visible organisms on Gram stain |
| S. aureus | Post-viral illness, empyema/abscess, gram-positive cocci in clusters |
5. Diagnostic Criteria
Clinical Diagnosis
CAP is suspected with new pulmonary infiltrate on chest X-ray plus ≥2 of the following:
- Fever (>38°C) or hypothermia (<35°C)
- New or worsening cough (with or without sputum)
- New or worsening dyspnea
- Pleuritic chest pain
- New focal chest signs (bronchial breathing, crackles, dullness)
- Leukocytosis (WBC >10×10⁹/L) or leukopenia (<4×10⁹/L)
Investigations
- Chest X-ray: Mandatory — confirms infiltrate, lobar vs. interstitial vs. cavitation
- CT chest: More sensitive; detects necrosis, obstruction, empyema, bronchiectasis; useful in immunocompromised
- CBC: Leukocytosis (bacterial) or leukopenia/lymphopenia (viral)
- Sputum Gram stain and culture: Recommended for hospitalized patients, especially severe CAP or MRSA/Pseudomonas risk
- Blood cultures: Yield 5–14% in hospitalized patients; reserved for neutropenia, asplenia, severe CAP, MRSA/Pseudomonas risk
- Urinary antigen tests: Legionella pneumophila serogroup 1 (sensitivity 70%, specificity 99%); pneumococcal antigen (sensitivity 70%, specificity >90%) — for severe cases
- PCR panels (multiplex): Standard for viral pathogens; also detects Legionella, M. pneumoniae, C. pneumoniae
- Procalcitonin (PCT): Elevated in bacterial infection; NOT sufficient to withhold antibiotics in confirmed CAP (IDSA/ATS strong recommendation)
- CRP: Less sensitive than PCT; should supplement, not supplant, clinical judgment
6. Choice of Treatment Site: CRB-65 Scale
The CRB-65 is a simplified severity scoring tool designed for outpatient/primary care use (no blood tests required), derived from the CURB-65 score.
CRB-65 Criteria (1 point each)
| Criterion | Definition |
|---|---|
| C — Confusion | New disorientation (person, place, time) |
| R — Respiratory rate | ≥30 breaths/min |
| B — Blood pressure (low) | Systolic <90 mmHg or diastolic ≤60 mmHg |
| 65 — Age | ≥65 years |
Score Interpretation and Treatment Site
| Score | Mortality Risk | Recommended Action |
|---|---|---|
| 0 | <1% | Low risk → Outpatient (polyclinic) treatment |
| 1–2 | ~5–12% | Moderate risk → Consider hospital admission or close outpatient follow-up |
| 3–4 | >30% | High risk → Urgent hospital/ICU admission |
Patients with CRB-65 score <2 have low mortality, but neither CRB-65 nor CURB-65 is as thoroughly validated as the full Pneumonia Severity Index (PSI/PORT score). Clinical judgment remains essential.
CURB-65 (hospital setting, adds U = urea >7 mmol/L, i.e., BUN >19 mg/dL) is used when lab results are available.
7. Principle of Antibiotic Therapy Selection (Outpatient/Polyclinic)
Therapy is empirical, guided by:
- Severity of illness (CRB-65 score)
- Presence of comorbidities or modifying risk factors
- Local resistance patterns
- Prior antibiotic use (past 3 months)
Outpatient CAP — Antibiotic Regimens (Harrison's Table 131-4; Fishman's)
No comorbidities, no resistance risk factors:
- Amoxicillin 1 g TID (monotherapy), OR
- Doxycycline 100 mg BID (monotherapy), OR
- Macrolide (azithromycin 500 mg day 1, then 250 mg days 2–5; clarithromycin 500 mg BID) — only if local pneumococcal resistance <25%
- Combination: Amoxicillin + macrolide or doxycycline
With comorbidities (chronic heart/lung/liver/kidney disease, DM, alcoholism, malignancy, asplenia) or resistance risk:
- Amoxicillin/clavulanate (875/125 mg BID or 500/125 mg TID) + macrolide or doxycycline, OR
- Respiratory fluoroquinolone monotherapy: levofloxacin 750 mg/day, moxifloxacin 400 mg/day, gemifloxacin 320 mg/day
Duration of therapy: Typically 5–7 days for uncomplicated outpatient CAP (minimum 5 days; patient must be afebrile for 48–72 hours before stopping).
Key Principles
- Cover both typical (S. pneumoniae, H. influenzae) and atypical organisms (Mycoplasma, Chlamydophila, Legionella) in most outpatient regimens
- Fluoroquinolones should be reserved for patients with comorbidities or failure/intolerance of first-line agents (CDC stewardship guidance)
- Adjust if culture/sensitivity results become available
- Add MRSA or Pseudomonas coverage only if prior respiratory isolation or validated risk factors are present
8. Assessing Antibiotic Effectiveness at the Polyclinic
Initial reassessment at 48–72 hours after starting therapy:
Signs of Effective Treatment (Response Expected)
- Fever resolution (temperature normalizing)
- Improvement in respiratory rate and oxygen saturation
- Decreased cough and sputum production
- Improved general condition, appetite, and functional status
- WBC trending toward normal
- CRP/PCT declining
Signs of Treatment Failure — Reassess and Modify
| Situation | Action |
|---|---|
| No improvement at 48–72 h | Reconsider diagnosis, pathogen, and resistance |
| New or worsening symptoms | Consider hospitalization; obtain cultures if not done |
| Atypical pathogens suspected | Ensure macrolide or doxycycline is included |
| Legionella/resistant organisms | Consider fluoroquinolone or add agent |
| Marked clinical deterioration | Immediate hospital admission |
Criteria for Hospitalization (from Outpatient)
Upgrade to inpatient if CRB-65 score increases, if O₂ saturation <94%, if unable to tolerate oral medications, social circumstances are inadequate, or if no clinical improvement after 48–72 h of appropriate outpatient therapy.
Radiographic Follow-Up
- Chest X-ray should be repeated at 4–6 weeks after treatment to confirm radiographic clearance, especially in:
- Patients >50 years
- Smokers
- Those with persistent symptoms
- To exclude an underlying malignancy or persistent consolidation
Sources:
- Fishman's Pulmonary Diseases and Disorders (Tables 125-2, Fig. 125-1)
- Harrison's Principles of Internal Medicine 22E (Tables 131-4, 131-5)
- Tintinalli's Emergency Medicine (Tables 65-1 through 65-7, 65-10, 65-11)
- Goldman-Cecil Medicine, International Edition
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