Pneumonia is an acute infection of the lung parenchyma, involving the alveoli and surrounding interstitial tissues, which fill with exudate and inflammatory cells. Despite advances in antimicrobial therapy, pneumonia remains a leading cause of hospitalization and mortality worldwide. Understanding its classification, recognizing the clinical presentation, implementing risk stratification tools like CURB-65, and promoting pneumococcal vaccination are essential for clinical management and prevention.
Clinical Classification and Etiology
Pneumonia is classified based on the setting in which it was acquired, which guides empirical antimicrobial therapy:
- Community-Acquired Pneumonia (CAP): Acquired outside of healthcare settings. The most common bacterial pathogen is Streptococcus pneumoniae (pneumococcus), followed by Haemophilus influenzae, Moraxella catarrhalis, and atypical pathogens (Mycoplasma pneumoniae, Chlamydia pneumoniae, Legionella pneumophila). Viral pathogens include influenza, respiratory syncytial virus (RSV), and SARS-CoV-2.
- Hospital-Acquired Pneumonia (HAP) and Ventilator-Associated Pneumonia (VAP): Developed ≥ 48 hours after admission or endotracheal intubation. These are frequently caused by multidrug-resistant (MDR) pathogens, such as Pseudomonas aeruginosa, Methicillin-Resistant Staphylococcus aureus (MRSA), and Klebsiella pneumoniae.
Clinical Presentation and Physical Examination
The classic presentation of pneumonia includes fever, chills, a productive cough (with purulent or blood-streaked sputum), dyspnea, and pleuritic chest pain (worse with deep breathing or coughing). Physical examination reveals signs of pulmonary consolidation, including tachypnea, tachycardia, dullness to percussion, increased tactile fremitus, bronchial breath sounds, and crackles on auscultation. Early symptoms can be confused with upper respiratory tract infections or bronchial irritation; patients should differentiate their symptoms by reviewing Common Cold vs. Influenza and Acute Bronchitis to prevent progression.
Confirming a diagnosis of pneumonia requires a chest radiograph demonstrating a new lobar or segmental infiltrate, consolidation, or interstitial opacity.
💡 💡 Geriatric Pneumonia Presentation
In elderly patients, the classic symptoms of pneumonia (fever, productive cough) are frequently absent or blunted. Geriatric pneumonia often presents atypically with acute cognitive decline (delirium or confusion), falls, generalized weakness, hypothermia, or tachypnea. A high index of suspicion and low threshold for chest imaging are required in this population.
Risk Stratification and Severity Assessment: CURB-65
To determine the appropriate clinical setting for treatment (outpatient, general medical ward, or Intensive Care Unit), clinicians use the CURB-65 scoring system. One point is awarded for each of the following criteria:
- C – Confusion: Acute onset of disorientation in person, place, or time.
- U – Urea: Blood Urea Nitrogen (BUN) level > 19 mg/dL (> 7 mmol/L).
- R – Respiratory Rate: ≥ 30 breaths per minute.
- B – Blood Pressure: Systolic BP < 90 mmHg or Diastolic BP ≤ 60 mmHg.
- 65 – Age: ≥ 65 years.
Scoring Interpretation:
- Score 0-1: Low risk. outpatient management is generally safe.
- Score 2: Moderate risk. Consider short inpatient stay or close outpatient monitoring.
- Score ≥ 3: High risk. Inpatient admission is indicated, with consideration for ICU admission if the score is 4 or 5.
Prevention through Pneumococcal Vaccination
Pneumococcal vaccination is the primary strategy for reducing the burden of invasive pneumococcal disease (IPD) and pneumonia. Current CDC Advisory Committee on Immunization Practices (ACIP) guidelines recommend two types of vaccines for adults:
- Pneumococcal Conjugate Vaccines (PCV15 or PCV20): These induce a T-cell-dependent immune response, leading to mucosal immunity and immunological memory.
- Pneumococcal Polysaccharide Vaccine (PPSV23): Covers 23 serotypes but induces a T-cell-independent response, which does not produce long-term memory.
Adults aged ≥ 65 years who have not previously received a conjugate vaccine should receive a single dose of PCV20, or a single dose of PCV15 followed by a dose of PPSV23 one year later. Vaccination is also recommended for adults aged 19 to 64 with chronic medical conditions (e.g., COPD, diabetes, chronic heart disease) or immunocompromising states.
💡 Frequently Asked Questions (FAQ)
📚 References & Sources
- Metlay, J. P., et al. (2019). Diagnosis and Treatment of Adults with Community-acquired Pneumonia. American Journal of Respiratory and Critical Care Medicine, 200(7), e45-e67.
- Kobayashi, M., et al. (2022). Use of 15-Valent Pneumococcal Conjugate Vaccine and 20-Valent Pneumococcal Conjugate Vaccine Among U.S. Adults: Updated Recommendations of the Advisory Committee on Immunization Practices — United States, 2022. MMWR, 71(4), 109-117.
- Lim, W. S., et al. (2003). Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax, 58(5), 377-382.