165.3 🩺 內科專科考前版

165.3.0.1 1⃣ Urinary Antigen 局限

  • L. pneumophila serogroup 1 only
  • Misses ~ 20% (other serogroups + species)
  • Negative does NOT rule out → 仍 culture / PCR if high suspicion
  • 旅遊 hx + cooling tower exposure + clinical clue → empirical anyway

165.3.0.2 2⃣ 為䜕 β-lactam 沒甚?

  • Legionella is facultative intracellular in alveolar macrophage
  • β-lactams 䞍 penetrate cells well
  • Macrolide, FQ, doxycycline 郜 intracellular → cover Legionella
  • IDSA / ATS 2019 CAP guidelines: empirical 必 cover atypicals (esp. severe / ICU)

165.3.0.3 3⃣ Hospital-Acquired Legionellosis

  • 由 hospital water systems
  • BMT, transplant, ICU 高 risk
  • 通報 (any hospital-onset Legionella → outbreak investigation)
  • Prevention: water system monitor, copper-silver ionization, chlorination, point-of-use filters in high-risk

165.3.0.4 4⃣ 鑑別 Atypical CAP

Pathogen Clinical Clue
Legionella 重病, GI, neuro, hyponatremia, smoker, > 50
Mycoplasma Young, dry cough, headache, bullous myringitis, cold agglutinin, neuro (transverse myelitis), 玅疹 (EM)
Chlamydia pneumoniae Young + Older mixed, milder, prolonged cough
Chlamydia psittaci Bird exposure (psittacosis); hepatosplenic
Coxiella (Q fever) Cattle / sheep / 動物 birth fluids; hepatic, IE, Q fever fatigue syndrome

165.3.0.5 5⃣ Empirical CAP Therapy (IDSA/ATS 2019)

  • Outpatient healthy: amox high-dose + macrolide OR doxy alone
  • Outpatient comorbid: amox-clav / 2-3 gen ceph + macrolide / doxy OR respiratory FQ
  • Inpatient non-ICU: β-lactam + macrolide OR respiratory FQ
  • ICU: β-lactam + macrolide / FQ; consider broader for risk factors
  • Atypicals covered by macrolide / doxy / FQ in all regimens

165.3.0.6 6⃣ Outbreak Investigation

  • 2 cases linked geographically/temporally → outbreak
  • WGS / PFGE link clinical to environmental isolate
  • ID exposure (cooling tower, hot tub, etc.)
  • Remediation: drain + disinfect + retest
  • 通報 CDC + Local Health Department

165.3.0.7 7⃣ Pontiac vs Legionnaires’

Feature Pontiac Legionnaires’
Symptoms Flu-like, self-limit Pneumonia, severe
Mortality 0 5-30%
Attack rate High (90%+) Low (1-5%)
Pneumonia No Yes
Treatment None Abx
Pathogenesis Toxin (LPS) Invasive
Incubation 1-2 d 2-10 d

165.3.0.8 8⃣ 健保 / Taiwan

  • 通報 (notifiable)
  • Cluster cases → 衛生局 investigation
  • Hospital ICU / BMT — water system monitoring
  • 健保 levofloxacin / azithromycin covered for CAP / Legionella indication
  • 盧醫垫 hint: smoker + DM/CKD + severe pneumonia + hyponatremia → urine antigen å°± send