Infectious Lung Disease

Smoking can damage the mucociliary apparatus. Alcoholic stupor can interfere with epiglottic and cough reflexes (leads to aspiration pneumonia).

Community-acquired bacterial pneumonia

Sudden onset high fever with productive cough. Signs of consolidation: dullness to percussion, increased vocal tactile fremitus, egophony, lobar or patchy radiodensities on CXR. Alveolae filled with exudate, mostly PMNs.

Pneumococcus is classic lobar pneumonia: congestion, red hepatization, gray hepatization, resolution. Resolution can result in fibrosis, organizing pneumonia.

Haemophilus influenza is classic bronchopneumonia: usually lower lobes or right middle lobe, patchy in distribution, begins as bronchitis and spreads locally into lungs.

Community-acquired atypical pneumonia

Insidious onset with low-grade fever, nonproductive cough, flu-like symptoms: pharyngitis, laryngitis, myalgias, headache; no signs of consolidation on physical exam. Patchy interstitial infiltrate on CXR. Alveolae clear, interstitial mononuclear infiltrate. May see hyaline membrane as in ARDS.

Mycoplasma pneumoniae

Viruses: Respiratory syncytial virus, Influenza A and B

Influenzaviruses (RNA genome) have two major virulence factors: (1) hemagglutinin -- binds virus to cell receptors in nasal passages; (2) neuraminadase -- dissolves mucus, promotes release and dissemination of virus particles. Antigenic drift and antigen shift: latter requires new vaccine. Use of aspirin as treatment associated with Reye syndrome. Also associated with Guillain-Barre (not just C. jejuni).

Nosocomial pneumonia

Staph aureus, Gram negative rods (Enterobacteriaceae, Pseudomonas)

Aspiration pneumonia

Anaerobes from oral cavity (Bacteroides, Prevotella, Fusobacterium, Peptostreptococcus); aspiration of gastric acid part of pathology; right lobe usually affected and depends on position (upright -- posterobasal lower lobe; supine -- superior lower lobe; right-sided -- middle lobe and posterior upper lobe).

Abscess

Usually a complication of (1) aspiration (mostly oral anaerobes); (2) bacterial pneumonia (most commonly, Staph aureus and Klebsiella pneumoniae), (3) septic embolism (from bacterial endocarditis), or (4) obstructive cancer (bronchogenic carcinoma). Foul-smelling sputum since usually have mixed aerobic/anaerobic infection. Cavitary lesions on CXR with air-fluid levels.

HIV-specific pneumonias

Cytomegalovirus -- basophilic inclusions in nuclei of alveolar macrophages, endothelial cells, epithelial cells look like owl's eyes

Pneumocystis pneumonia -- "intra-alveolar foamy exudate," yeast that looks like "flattened ping-pong balls," require CD4 levels lower than 200, an AIDS defining infection, treat with TMP-SMX.

Aspergillus -- acute-angled branching septated hyphae (45 degrees), forms aspergillomas in cavitary lesions (e.g., TB) and cause hemoptysis, allergic aspergillosis (Type I and Type III hypersensitivities) causes interstitial lung disease and bronchiectasis, invasive aspergillosis of vessel walls causing hemorrhagic infarctions and necrotizing bronchopneumonia. Treat with voriconazole.

Bronchiectasis

Permanent fibrotic dilatation of bronchi and bronchioles caused by inflammatory destruction of muscle and elastic tissue, resulting from chronic necrotizing infections. Associated with cystic fibrosis, primary ciliary dyskinesia, and obstruction (cancer). Dilation all the way out to pleural surface (usually can't see 2-3cm from surface). Severe, persistent cough with bloody and/or foul-smelling sputum (coughing only way to get mucus out).