317.3 🏥 內科專科考前版

317.3.1 Mechanistic Deep Dive

317.3.1.1 S. pneumoniae Pathobiology

  • Polysaccharide capsule (immune evasion)
  • Pneumolysin
  • Spreads via aerosol
  • Vaccination + herd immunity → reduction
  • Antibiotic resistance (penicillin, macrolide)

317.3.1.2 Legionella Biology

  • Intracellular pathogen (macrophages)
  • Water-borne (cooling towers, hot tubs, humidifiers)
  • 50+ serogroups; type 1 most common in humans
  • Atypical features: GI, neurologic, hepatic, renal

317.3.1.3 Atypical Pathogens

  • No cell wall (Mycoplasma) — β-lactams ineffective
  • Macrolide / tetracycline / fluoroquinolone needed
  • Extracellular and intracellular

317.3.2 Recent Trials & Updates

317.3.2.1 CAPE COD (2023) — Hydrocortisone for Severe CAP

  • Hydrocortisone 200 mg/d × 4-8 days
  • ↓ 28-day mortality 5.7%
  • Practice-changing for severe non-COVID CAP

317.3.2.2 CORTICAP (2023) — Corticosteroids in COVID + CAP

  • Reaffirms dexamethasone in COVID
  • Tailored to non-COVID severe CAP

317.3.2.3 PCV20 Approval (2024)

  • Single dose adult immunization
  • Broader serotype coverage
  • Replaces PCV13 in many adult immunization

317.3.2.4 RSV Vaccines for Adults (2023)

  • Arexvy (GSK), Abrysvo (Pfizer)
  • ≥ 60 + chronic disease
  • ↓ Hospitalization 70-80% (1-2 seasons)

317.3.2.5 Procalcitonin-Guided Therapy

  • Stewardship benefits
  • ProCAP, ProHosp trials
  • Antibiotic-free days
  • ↓ Duration without harm

317.3.2.6 IDSA/ATS 2019 + 2024 Updates

  • Reaffirms combination therapy for inpatient/ICU
  • Emphasizes severity-based stratification
  • HCAP eliminated as separate category
  • Local resistance considered

317.3.2.7 Bedaquiline for MDR-Pneumonia (under investigation)

  • Limited role currently
  • Reserved for specific resistant organisms

317.3.3 High-Yield Specialist Points

317.3.3.1 Empiric Failure

  • Within 72 hours of antibiotics
  • Reconsider:
    • Antibiotic-resistant pathogen
    • Atypical / unusual pathogen (PCP, fungal, TB, parasitic)
    • Non-infectious cause (PE, malignancy, ILD, vasculitis)
    • Complication (empyema, abscess, septic embolus)
    • Alternative diagnosis

317.3.3.2 Multidrug-Resistant Strep

  • High-level penicillin resistance: cefotaxime, ceftriaxone, fluoroquinolone, vancomycin
  • Macrolide resistance: > 25% in many areas
  • Local epidemiology matters

317.3.3.3 CAP + Underlying Conditions

  • HIV: PCP, MTb, S. pneumoniae
  • COPD: H. influenzae, Pseudomonas (severe)
  • DM: GNR
  • Asplenia: encapsulated organisms (S. pneumoniae, H. influenzae)
  • IVDU: S. aureus, anaerobes
  • Alcohol: Klebsiella, S. aureus, anaerobes, S. pneumoniae

317.3.3.4 Severe Atypical Pneumonia Differential

  • Legionella
  • Mycoplasma (rare severe)
  • Chlamydia psittaci (psittacosis)
  • Coxiella burnetii (Q fever)
  • Francisella tularensis (tularemia)

317.3.3.5 Lung Abscess

  • Aspiration (anaerobes)
  • Septic embolus (S. aureus)
  • Cavitary pneumonia
  • Treatment: amoxicillin-clavulanate or clindamycin × 4-6 weeks

317.3.3.6 Post-Influenza Pneumonia

  • S. aureus (often MRSA), S. pneumoniae, GNR
  • Higher mortality
  • Aggressive treatment

317.3.3.7 Procalcitonin in Practice

  • 0.25 ng/mL: likely bacterial; consider antibiotics

  • < 0.1 ng/mL: bacterial unlikely; consider holding
  • Trending down: consider stopping antibiotics
  • Caveats: trauma, surgery, severe shock can elevate

317.3.3.8 Sputum Quality

  • Adequate: > 25 PMN, < 10 epithelial per LPF
  • Inadequate: too many epithelial cells (oral contamination)
  • Repeat if poor quality

317.3.3.9 Bronchoscopy Indications

  • Non-resolving pneumonia
  • Immunocompromised
  • Suspected obstructing lesion (malignancy, foreign body)
  • Failed empiric therapy

317.3.3.10 Aspiration Pneumonia (Ch318 Details)

  • Polymicrobial; anaerobes predominant
  • Dependent lobes (RLL > LLL when supine)
  • Watch for abscess, empyema

317.3.3.11 CAP + Cardiac Events

  • ↑ MI, AF, HF, stroke during + after pneumonia
  • Up to 30 days post-discharge
  • Multifactorial (inflammation, hypoxia, sympathetic)
  • Standard CV care + secondary prevention

317.3.4 Pearls

  • S. pneumoniae most common bacterial CAP
  • Legionella: hyponatremia, GI, hepatic; urinary antigen
  • CURB-65: outpatient (0-1) vs admit (≥ 2) vs ICU (≥ 4)
  • Outpatient healthy: amoxicillin or doxy
  • Inpatient non-ICU: β-lactam + macrolide OR fluoroquinolone
  • ICU: β-lactam + macrolide
  • Severe CAP: hydrocortisone 200 mg/d × 4-8 days (CAPE COD)
  • Vaccines 2024: PCV20, RSV for ≥ 60 + risk factors
  • Procalcitonin: stewardship + duration guidance