Pneumonia and Its Pathogenesis

Study Notes

An acute infection with consolidation within a lung, affecting part or all of one or both lungs
Classified into Community-Acquired Pneumonia (CAP), Hospital-Acquired Pneumonia (HAP), and Ventilator-Associated Pneumonia (VAP)
Pneumonia types are differentiated by where they are acquired and treated with different antibiotics
Causes include bacteria, viruses, fungi, and parasites

Factors that suppress cough increase pneumonia likelihood like cerebrovascular stroke
Inhibited cilia via causes like smoking or immotile cilia also increase susceptibility
Defective macrophage and neutrophil function caused by aging, chronic disease, HIV, corticosteroid, or chemotherapy leads to impaired phagocytosis of microorganisms
Impaired immunoglobulin production in lungs (IgA) also contributes to increased risk

Inhalation is the most common route of transmission followed by Aspiration
Colonization through pre-existing lung diseases such as bronchiectasis, chronic bronchitis, smoking, or IV drug addiction also contribute
Spread through blood can occur in cases of bacteremia or IV drug addiction

Lung tissue develops consolidation characterized by exudate, inflammatory cells, and fibrin
Consolidation progresses through distinct stages: congestion, red hepatization, gray hepatization and finally, resolution
Resolution occurs over 7-10 days with incomplete resolution leading to permanent scarring

Common pneumonia pathogens include Streptococcus pneumoniae, Haemophilus influenzae, and Atypical Bacteria
Pseudomonas aeruginosa or Methicillin-resistant Staphylococcus aureus (MRSA) infection risk is increased by recent hospitalization, IV antibiotic treatment within 90 days, or pre-existing comorbidities
Comorbidities increasing risk include chronic heart, lung, liver, or renal disease (dialysis); diabetes mellitus; alcoholism; malignancy; or asplenia.

Clinical picture of pneumonia can present with vague symptoms, especially in elderly patients
Common symptoms include fever, tachycardia (fast heart rate), hypotension (low blood pressure), tachypnea (rapid breathing), and reduced SpO2% (respiratory failure)
Examination reveals cyanosis (bluish discoloration), working accessory muscles, dull percussion, and diminished breath sounds with bronchial breathing and crackles
Chest X-ray, CT Chest, and laboratory tests are important adjuncts to diagnosis

Complete Blood Picture (CBC) helps determine levels of white blood cells
Arterial Blood Gases assess oxygen and carbon dioxide levels in the blood
Blood Urea Nitrogen screens for kidney function
PCR for viral antigen detection in sputum/nasopharyngeal swab detects viral causative agents
Sputum Gram stain helps identify bacteria and their morphology
Sputum Culture & Sensitivity identify specific bacterial species and their susceptibility to antibiotics
Blood Culture & Sensitivity are performed if high risk or severe pneumonia is suspected to identify bacteria present in bloodstream

CURB-65 score is used to assess severity and determine appropriate treatment site
CURB-65 Score 0-1 suggests home treatment (outpatient), 2 suggests hospital ward, 3-5 or severe CAP suggests ICU treatment

Inpatient and outpatient antibiotic doses differ based on severity
Amoxicillin, Doxycycline, Ceftriaxone are some beta-lactam antibiotics
Macrolides such as azithromycin are commonly used
Fluoroquinolones like Levofloxacin are also often used
Specific antibiotics like piperacillin-tazobactam, meropenem, vancomycin, or linezolid are chosen depending on the identified bacteria

Molecular testing for Influenza virus is necessary
Anti-viral drugs, such as Oseltamivir, are added to the empirical antibiotic regimen if a viral infection is confirmed

Specific anti-anaerobic antibiotics are added to the empirical antibiotic regimen only if a lung abscess or empyema is suspected
Antibiotic therapy should last at least five days