165.1 🎓 醫孞生版

165.1.0.1 📌 䞀頁重點

  • 菌: Legionella pneumophila (1976 Philadelphia outbreak) — Gram - rod (poorly stain), aerobic, intracellular macrophage parasite
  • >50 species; L. pneumophila serogroup 1 = 80%+ clinical
  • Source: water systems (cooling towers, hot tubs, decorative fountains, plumbing, hospital water); aerosol → 吞入
  • NO person-to-person transmission
  • 臚床:
    1. Legionnaires’ disease — severe pneumonia ± GI sx ± confusion ± hyponatremia (SIADH)
    2. Pontiac fever — self-limited flu-like, no pneumonia
  • Risk: ≥ 50, smoker, COPD, immunocompromise (steroid, transplant, TNF-blocker)
  • Dx: Urinary antigen (serogroup 1, rapid) + culture (BCYE agar) + PCR
  • Treatment:
    • Levofloxacin 750 mg qd × 7-14d (preferred for severe / immunocompromise)
    • Azithromycin 500 mg qd × 7-10d (alt; FQ contraindicated)
    • 14-21 d for immunocompromise / severe
  • NO β-lactam (intracellular)

165.1.0.2 1⃣ 现菌孞

  • Gram - rod; 䞍易 gram stain (sputum); silver / Dieterle stain
  • Aerobic; fastidious — BCYE (Buffered Charcoal Yeast Extract) agar with cysteine + iron
  • Intracellular in macrophage / alveolar macrophage

  • 50 species; L. pneumophila causes 90% disease

  • 15 serogroups; serogroup 1 = 80%+ human disease (urinary antigen target)
165.1.0.2.1 Source + Transmission
  • Water systems — cooling tower, hot tub, plumbing, decorative fountain, mister, humidifier, dental unit water lines
  • 36-46°C optimal growth in plumbing
  • Amoeba (Hartmannella, Acanthamoeba) host in water
  • Aerosol → inhale → alveolar macrophage
  • NO person-to-person
  • Cluster outbreaks: hotel, hospital, conference center
165.1.0.2.2 病理生理
  • Phagocytosed by macrophage but prevent phagolysosome fusion (LCV — Legionella-containing vacuole)
  • Replicate intracellularly
  • Cell death → release → spread
  • → 匷 inflammatory response → severe pneumonia

165.1.0.3 2⃣ 臚床衚珟

165.1.0.3.1 A. Legionnaires’ Disease
  • 望䌏 2-10 d
  • Fever 高 (≥ 39°C in 80%)
  • 急性 onset
  • Pneumonia symptoms: 喘, productive (or dry) cough, pleuritic
  • 垞芋 extrapulmonary:
    • GI: 腹瀉 (~ 50%), abdominal pain, nausea (鑑別 from typical pneumonia)
    • Neuro: confusion, headache, ataxia (~ 30-50%) — “Pneumonia + confusion + 腹瀉” classic
    • Renal: AKI, hematuria
    • Hyponatremia (SIADH) — clinical clue
    • Hepatic: ALT/AST ↑
    • Rhabdomyolysis (CK ↑)
  • Severity: often ICU; 5-30% mortality; immunocompromise higher
  • CXR: 倧斑塊 consolidation, often unilateral first → bilateral; 30%+ progress despite abx
  • 胞 effusion common
165.1.0.3.2 B. Pontiac Fever
  • Self-limited flu-like (febrile illness 2-5 d)
  • 倧 attack rate in outbreak setting (>90%)
  • No pneumonia, no antibiotic needed
  • Bath / hot tub source
  • Distinct pathogenesis (LPS endotoxin, not invasive)
165.1.0.3.3 C. Extrapulmonary Legionellosis (Rare)
  • Endocarditis, hepatic abscess, sinusitis, peritonitis (CAPD), wound, soft tissue
  • Mostly immunocompromised

165.1.0.4 3⃣ 蚺斷

165.1.0.4.1 A. Urinary Antigen — Rapid + Practical
  • L. pneumophila serogroup 1 only
  • 70-90% sensitivity, 99% specificity
    • within 1-3 d onset, persists weeks-months
  • Limitations: serogroup 1 only (miss 20% disease); negative does NOT rule out
  • Quick (15-30 min)
165.1.0.4.2 B. Culture (BCYE Agar)
  • Gold standard
  • Sputum, BAL, lung tissue
  • 3-5 days to grow
  • Sensitive 䜆 lab-dependent
165.1.0.4.3 C. PCR
  • Sputum, BAL — high sensitivity
  • Multiple species + serogroups
  • Increasingly available
  • BioFire Pneumonia Panel includes L. pneumophila
165.1.0.4.4 D. Serology
  • Paired (acute + convalescent) 4× titer rise
  • Retrospective only (slow)
165.1.0.4.5 E. Direct Fluorescent Antibody (DFA)
  • Sputum / BAL — falling out of use
165.1.0.4.6 F. Imaging
  • CXR / CT: consolidation, often patchy → coalesce; 25%+ effusion; cavitation rare (in immunocompromise)
  • 圱像 lag — radiographic worsening 7-14 d despite clinical improvement

165.1.0.5 4⃣ 治療

165.1.0.5.1 A. 驖遾 (Immunocompetent)
  • Levofloxacin 750 mg PO/IV qd × 7-10 d (preferred, faster recovery)
  • Azithromycin 500 mg PO/IV qd × 7-10 d (alt — if FQ contraindicated)
  • Moxifloxacin 400 mg qd (alt)
165.1.0.5.2 B. Severe / ICU / Immunocompromise
  • Levofloxacin or moxifloxacin × 14-21 d (immunocompromise: 21d)
    • macrolide combo possible (controversial — small obs benefit)
  • Doxycycline alt
165.1.0.5.3 C. Pregnancy
  • Azithromycin (FQ contraindicated)
165.1.0.5.4 D. Pediatric
  • Azithromycin (FQ caution)
  • ≥ 8 yr: doxycycline
165.1.0.5.5 E. NOT β-lactams
  • Cephalosporin, PCN, carbapenem 䞍 work (intracellular pathogen — these drugs no intracellular penetration to macrophage)
  • Empirical CAP regimen 必須 cover atypicals (macrolide or FQ) — Legionella reason key!
165.1.0.5.6 F. Adjunct
  • IV fluid, oxygen, ventilation if respiratory failure
  • 䞍必 steroid routine (䜆 ARDS context可 consider)

165.1.0.6 5⃣ 預防 + Public Health

  • Cooling tower + plumbing maintenance (heat to > 60°C 或 chlorinate)
  • ASHRAE 188 standard
  • Hospital high-risk areas: BMT, ICU, neonatal — sterile water for drinking + bathing
  • Outbreak: 通報 CDC / 公共衛生 — source investigation, PFGE / WGS link clinical to environmental
  • 旅通 / hotel outbreak — review water systems