Cardiology

Background 

I) Definition 

Bacterial pneumonia is an acute infection of the lung parenchyma caused by bacterial pathogens, leading to alveolar inflammation and consolidation. It results in impaired gas exchange, hypoxia, and systemic inflammatory response. Characterized clinically by cough, fever, dyspnea, and pleuritic chest pain, it remains a major cause of morbidity and mortality, especially in the very young, elderly, and those with chronic illnesses or immunosuppression. 

II) Classification/Types 

By Setting: 

• Community-acquired pneumonia (CAP): Acquired outside of healthcare settings. 

• Hospital-acquired pneumonia (HAP): Onset ≥48 hours after hospital admission. 

• Ventilator-associated pneumonia (VAP): Onset ≥48 hours after endotracheal intubation. 

• Aspiration pneumonia: Caused by inhalation of oropharyngeal/gastric contents, typically involving anaerobic bacteria. 

By Causative Organism: 

• Typical Bacteria: 

• Streptococcus pneumoniae (most common CAP) 

• Haemophilus influenzae 

• Staphylococcus aureus 

• Klebsiella pneumoniae 

• Atypical Bacteria: 

• Mycoplasma pneumoniae 

• Chlamydophila pneumoniae 

• Legionella pneumophila 

• Nosocomial Pathogens: 

• Pseudomonas aeruginosa 

• Multidrug-resistant gram-negative bacilli 

• MRSA (Methicillin-resistant Staphylococcus aureus) 

By Radiologic Pattern: 

• Lobar pneumonia: Uniform consolidation of a lung lobe. 

• Bronchopneumonia: Patchy infiltrates scattered in multiple lobes. 

• Interstitial pneumonia: Reticulonodular opacities in the interstitium, more common in atypical organisms. 

Pathophysiology 

Inhaled or aspirated bacteria colonize the alveoli, overwhelming host defenses. Neutrophils and macrophages migrate to the site, releasing cytokines (e.g., IL-6, TNF-α), which increase capillary permeability and promote alveolar exudate. The alveoli fill with fluid and immune cells, impairing ventilation-perfusion matching and gas exchange. Systemic inflammatory response may lead to fever, tachycardia, and sepsis. Severe disease can result in hypoxemic respiratory failure, lung abscess, or empyema. 

Epidemiology 

• Annual CAP incidence: 5–7 per 1,000 adults in the U.S. 

• HAP and VAP are among the leading hospital-acquired infections. 

• Streptococcus pneumoniae is the most common bacterial cause of CAP worldwide. 

• Risk factors include advanced age, chronic disease, smoking, alcoholism, and immunosuppression. 

• Mortality: <1% in healthy outpatients, but up to 20–30% in ICU settings with VAP. 

Etiology 

I) Common Bacterial Pathogens 

II) Risk Factors 

• Age >65 or <5 years 

• Smoking and alcohol use 

• COPD, asthma, bronchiectasis 

• Diabetes mellitus 

• Malignancy 

• HIV/AIDS or other immunocompromised states 

• Neurologic impairment (stroke, dementia, seizures) 

• Recent hospitalization or antibiotic use 

• Mechanical ventilation 

Clinical Presentation 

I) History (Symptoms) 

• Sudden or gradual onset of: 

• Fever and chills 

• Cough (productive or dry) 

• Dyspnea and tachypnea 

• Pleuritic chest pain 

• Fatigue, malaise, or confusion (especially in elderly) 

II) Physical Exam (Signs) 

• Fever, tachycardia, and hypoxia 

• Decreased breath sounds over affected area 

• Bronchial breath sounds, crackles (rales) 

• Egophony, whispered pectoriloquy 

• Dullness to percussion 

• Increased tactile fremitus 

Differential Diagnosis (DDx) 

• Acute bronchitis 

• Pulmonary embolism 

• Congestive heart failure 

• Lung abscess or empyema 

• Tuberculosis 

• COVID-19 pneumonia 

• Interstitial lung disease 

Diagnostic Tests 

Initial Evaluation 

• Chest X-ray: Confirms diagnosis; shows lobar consolidation or patchy infiltrates. 

• CBC: Leukocytosis with left shift. 

• Blood cultures: Especially in hospitalized or septic patients. 

• Sputum Gram stain and culture: Identify causative organism if possible. 

• Pulse oximetry / ABG: Assess oxygenation status. 

• Procalcitonin / CRP: May aid in determining bacterial etiology. 

• COVID-19 and Influenza testing: During outbreaks or flu season. 

Additional Testing 

• Urinary antigens: For Legionella and S. pneumoniae. 

• Bronchoscopy with lavage: In ICU or immunocompromised patients. 

• Chest CT: For complicated or non-resolving pneumonia. 

Treatment 

I) Acute Management 

Outpatient CAP (Empiric Therapy): 

• Healthy adults: 

• Amoxicillin or Doxycycline 

• With comorbidities: 

• Amoxicillin-clavulanate + Azithromycin 

• OR Levofloxacin monotherapy 

Inpatient (Non-ICU): 

• Ceftriaxone + Azithromycin 

• OR Levofloxacin 

ICU or Severe CAP: 

• Ceftriaxone + Azithromycin or Levofloxacin 

• Add Vancomycin or Linezolid for MRSA risk 

• Add Piperacillin-tazobactam for Pseudomonas risk 

Aspiration Pneumonia: 

• Ampicillin-sulbactam 

• OR Clindamycin 

II) Supportive Therapy 

• Oxygen therapy (nasal cannula, face mask, or mechanical ventilation) 

• IV fluids and electrolyte correction 

• Antipyretics for fever 

• Bronchodilators for wheezing 

• Corticosteroids in select cases (e.g., refractory hypoxia, severe COVID) 

Medications 

Device Therapy 

• Oxygen supplementation: Via nasal cannula, face mask, or high-flow oxygen 

• Non-invasive ventilation (BiPAP/CPAP): For moderate respiratory distress 

• Mechanical ventilation: In cases of respiratory failure or ARDS 

Patient Education, Screening, Vaccines 

• Adherence to prescribed antibiotics 

• Smoking cessation counseling 

• Hand hygiene and cough etiquette 

• Vaccines: 

• Pneumococcal vaccine (PCV15 or PCV20 + PPSV23) 

• Annual influenza vaccine 

• COVID-19 vaccination 

Consults/Referrals 

• Pulmonology: For severe or recurrent pneumonia 

• Infectious Disease: For resistant organisms or immunocompromised patients 

• Critical Care: For ICU admission 

• Speech Therapy: For aspiration risk evaluation 

Follow-Up 

Short-Term 

• Reassess clinical response within 48–72 hours 

• Monitor oxygenation and signs of improvement 

• Adjust antibiotics if culture results are available 

Long-Term 

• Chest X-ray in 6–8 weeks for high-risk patients 

• Monitor for complications: abscess, empyema, bronchiectasis 

• Consider pulmonary rehab in patients with prolonged illness or deconditioning 

Prognosis 

• Excellent in young, otherwise healthy patients with timely treatment 

• Mortality <1% in outpatient CAP 

• Poorer outcomes in ICU patients or those with comorbidities 

• Early antibiotics, supportive care, and vaccinations improve prognosis