Pneumonia: Classifications, Causes, and Facts

• Pneumonia is an acute lung parenchyma infection caused by one or more pathogens.
• In 2014, pneumonia was the 8th leading cause of death in the U.S.
• More than 100 million adult and pediatric pneumonia cases occur each year.
• Pneumonia incidence increases in colder climates and winter months.
• The elderly and immunocompromised individuals have higher pneumonia mortality.
• Pneumonia can be classified by causative organism, acquisition, anatomic location, and drug resistance.

Classifications by Causative Organism

• Bacterial
• Viral
• Fungal
• Parasitic

Classifications by Acquisition

• Community-acquired pneumonia (CAP)
• Hospital-acquired pneumonia (HAP)
• Ventilator-associated pneumonia (VAP)

Classifications by Anatomic Location

• Lobar pneumonia: Affects a distinct area of the lung, often seen in community-acquired pneumonia.
• Bronchopneumonia: Multifocal, affecting multiple regions in one or both lungs, often seen in hospital-acquired pneumonia.
• Interstitial pneumonia: Affects lung tissue between alveoli, typically from viral infections, leading to alveolar wall thickening.

Mechanisms of Infection

• Organisms invade and colonize the respiratory tract when host defenses are compromised.
• Entry occurs through inhalation of airborne particles, aspiration of secretions, and hematogenous spread from infections elsewhere.

Common Organisms

• Bacteria (most common)
• Viruses
• Atypical bacteria
• Fungi
• Parasites

Bacterial Pneumonia: Causative Agents

• Typical bacteria includes Streptococcus pneumoniae (most common), Staphylococcus aureus, Klebsiella pneumoniae, and Haemophilus influenzae. Atypical bacteria ("Walking Pneumonia") includes Mycoplasma pneumoniae (most common) and Legionella pneumophila (severe CAP).

Gram Staining

• Gram-positive stains purple.
• Gram-negative stains pink.

Types of Bacteria

• Aerobic bacteria requires oxygen.
• Anaerobic bacteria cannot survive in oxygen.
• Facultative anaerobes can grow with or without oxygen.

Morphology

• Cocci are round.
• Bacilli are rod-shaped.
• Spirilla are spiral-shaped.

Signs & Symptoms of Pneumonia

• Respiratory symptoms include productive cough and adventitious breath sounds
• Dull percussion is heard over areas of consolidation.
• Cardiac symptoms include tachycardia or bradycardia.
• Fever presents as high-grade (>101°F).
• Observation may reveal cyanosis and altered mental status.

Sputum Characteristics

• Rust-colored sputum indicates Streptococcus pneumoniae infection.
• Currant jelly sputum indicates Klebsiella pneumoniae infection.
• Green sputum indicates Pseudomonas aeruginosa or Haemophilus influenzae infection.
• Yellow sputum indicates typical bacterial infections.
• Foul-smelling sputum indicates anaerobic infections.

Risk Factors

• Age >65 years
• Chronic lung diseases
• Increased risk of microaspiration
• Immunocompromising conditions
• Metabolic disorders
• Instrumentation of the respiratory tract
• Recent viral infection (especially influenza)

Complications

• Acute Respiratory Distress Syndrome (ARDS)
• Bacteremia (blood infection)
• Bronchiectasis
• Lung abscess
• Septic shock
• Pleural effusion and pleurisy
• Multi-organ failure

Diagnostic Testing

• Chest X-ray (CXR) is the gold standard.
• Lobar consolidation indicates bacterial pneumonia.
• Patchy infiltrates indicates atypical pneumonia.
• Pneumatoceles suggest S. aureus infection.
• Laboratory tests include CBC (elevated WBC count with left shift) and blood & sputum cultures.
• CRP & procalcitonin helps distinguish pneumonia from other conditions.

Treatment & Management

• Empiric antibiotics are broad-spectrum initially, then targeted therapy.
• Bronchodilators are used if bronchospasm is present.
• Oxygen therapy is used for hypoxia.
• Administer mucolytics & airway clearance therapy, and hydration & rehydration therapy.
• Prognosis depends on severity, virulence, and host factors; most patients recover within 2 weeks with proper treatment.
• Acute Respiratory Distress Syndrome (ARDS)

Viral Pneumonia: Causative Agents

• Influenza virus (most common)
• Respiratory syncytial virus (RSV)
• Adenovirus
• Parainfluenza virus
• Rhinovirus
• Coronavirus

Signs and Symptoms

• Fever, chills
• Nonproductive cough
• Rhinitis (runny nose)
• Muscle aches, fatigue, headache
• Gradual onset compared to bacterial pneumonia

Diagnostic Testing

• Chest X-ray shows interstitial infiltrates.
• Arterial blood gas (ABG) depends on etiology.
• Sinus tachycardia may be present.
• CBC may be normal or show leukocytosis with lymphocytic predominance.
• Nasopharyngeal cultures are standard for viral pathogen identification.

Treatment

• Supportive care is provided with oxygen, fluids, and symptomatic treatment.
• Antivirals like Tamiflu (influenza) and Ribavirin (RSV) may be used.
• Antibiotics are not used unless a secondary bacterial infection occurs.

Prognosis

• Prognosis is usually self-limiting but can be severe in high-risk groups like the elderly, infants, and immunocompromised patients.

Key Takeaways

• Pneumonia can be bacterial, viral, or fungal.
• CAP is the most common type, while HAP/VAP carries higher mortality.
• Treatment includes antibiotics for bacterial, antivirals for viral, and antifungals for fungal infections.
• Preventative measures reduce hospital-acquired pneumonia.

Pneumonia is an acute lung infection with high incidence and mortality, especially in the elderly and immunocompromised. It's classified by causative organism (bacterial, viral, fungal, parasitic), acquisition (CAP, HAP, VAP), and anatomic location (lobar, bronchopneumonia, interstitial). Understanding these classifications is crucial for effective diagnosis and treatment.