178.1 🎓 醫孞生版

178.1.0.1 📌 䞀頁重點

  • 菌: Bordetella pertussis — gram - coccobacillus, fastidious, requires Bordet-Gengou or Regan-Lowe media, NAD-dependent
  • Toxins: Pertussis toxin (PT) (AB5, ADP-ribosylate Gi), adenylate cyclase toxin (ACT), tracheal cytotoxin, FHA (filamentous hemagglutinin), LOS
  • Reservoir: 人 only; highly contagious (R0 12-17, > measles)
  • 臚床 3 phases (classic 6-12 wk):
    1. Catarrhal (1-2 wk): rhinitis, mild cough, low fever — most contagious phase
    2. Paroxysmal (2-6 wk): paroxysmal cough + whoop inspiratory + post-tussive vomiting, normal between bursts
    3. Convalescent (≥ 2 wk): gradual decline; “100-day cough” in adults
  • 嬰兒 < 6 mo: 倚 atypical — apnea, cyanosis, no whoop; high mortality (pulmonary HTN, encephalopathy, secondary bacterial pneumonia)
  • 2024 resurgence: USA, China, EU — 倧幅 increase post-COVID immunity drop, waning vaccine immunity, anti-vaccine sentiment
  • Treatment:
    • Azithromycin 5d (preferred), Clarithromycin 7d, Erythromycin 14d
    • TMP-SMX alt if macrolide allergy / R
    • Best in catarrhal stage; paroxysmal stage abx 䞍 alter clinical course but reduces transmission
  • Prevention:
    • DTaP infant series (2/4/6/15-18 mo + 4-6 yr booster)
    • Tdap at 11-12 yr + once adult + 每次 pregnancy 27-36 wk (passive infant immunity)
    • 接觞者 prophylaxis: azithromycin (same dose as treatment)

178.1.0.2 1⃣ 现菌孞

  • Gram - coccobacillus
  • Fastidious — needs Bordet-Gengou agar (potato-glycerol-blood) or Regan-Lowe (charcoal-blood)
  • Slow grow (5-7 days)
  • NAD-dependent
  • Species:
    • B. pertussis (#1 clinical)
    • B. parapertussis — milder whooping cough
    • B. bronchiseptica — kennel cough in dogs, rare human
178.1.0.2.1 Virulence
  • Pertussis toxin (PT) — AB5 toxin, ADP-ribosylates Gi → cAMP ↑ → impaired lymphocyte function + lymphocytosis
  • Adenylate cyclase toxin (ACT) — entered host cells, ↑ cAMP, impairs phagocytic + immune function
  • Tracheal cytotoxin (TCT) — ciliated epithelium damage
  • Filamentous hemagglutinin (FHA) — adhesion to ciliated cells
  • Pertactin (PRN) — adhesin; some recent strains PRN-deficient — vaccine escape concern
  • Lipo-oligosaccharide (LOS) — endotoxin

178.1.0.3 2⃣ 臚床衚珟 (Classic — Older Child / Adult)

178.1.0.3.1 Phase 1: Catarrhal (1-2 wk)
  • Rhinitis, conjunctivitis, mild cough, low-grade fever
  • Indistinguishable from URI
  • Most contagious phase — but rarely diagnosed
  • Lymphocyte 升 (PT effect)
178.1.0.3.2 Phase 2: Paroxysmal (2-6 wk)
  • Paroxysmal cough: 5-15+ rapid consecutive coughs without inhalation between
  • Inspiratory whoop (after paroxysm — air rushing through narrowed glottis)
  • Post-tussive emesis
  • Cyanosis, facial vein engorgement during paroxysm
  • Normal interval between paroxysms (病人 looks well)
  • ≥ 14 days cough — classic case definition
178.1.0.3.3 Phase 3: Convalescent (≥ 2 wk)
  • Gradual decrease in paroxysm frequency + severity
  • “100-day cough” in adolescents/adults
  • Triggered by URI later (waning effect)
178.1.0.3.4 Complications
  • Pneumonia (primary or secondary bacterial — S. aureus, S. pneumo, H. influenzae)
  • Rib fracture (from severe paroxysms)
  • Urinary incontinence (paroxysm)
  • Hernia
  • Subconjunctival hemorrhage, epistaxis, syncope
  • Pertussis encephalopathy (rare)
  • Pertussis pneumonia in infants — high mortality

178.1.0.4 3⃣ 嬰兒 < 6 月

  • Atypical presentation — no whoop classic
  • Apnea, cyanosis, bradycardia, gasping
  • “Sick” infant with respiratory distress
  • High mortality (1-3% in young infants)
  • Secondary pulmonary hypertension + cardiopulmonary failure
  • Encephalopathy
  • Hospitalization standard
  • Maternal Tdap during pregnancy is single most important protective measure for infant

178.1.0.5 4⃣ 流行病孞

  • Pre-vaccine: 200,000 cases/yr in US, 5000 deaths/yr
  • DPT (1940s) → DTaP (1990s, less reactogenic but faster waning immunity)
  • Waning immunity: 5-10 yr after vaccine; Tdap booster needed
  • Resurgence in adolescents/adults — undetected reservoir → infant transmission
  • 2024 surges:
    • USA: 5-10× baseline cases
    • China: 5000+ cases/wk early 2024
    • EU: France, Spain, UK significant outbreaks
  • Drivers: post-COVID immunity drop, waning DTaP, anti-vaccine, PRN-deficient strains (vaccine escape)

178.1.0.6 5⃣ 蚺斷

  • PCR (nasopharyngeal swab) — most sensitive, especially first 3 wk
  • Culture (Bordet-Gengou or Regan-Lowe) — gold standard but slow + low sens after 1st wk
  • Serology — anti-PT IgG — late (≥ 2 wk paroxysmal); not for early diagnosis
  • Lymphocytosis (> 10,000-20,000) in classic pediatric — clue
  • 通報 (notifiable)

178.1.0.7 6⃣ 治療

178.1.0.7.1 A. Antibiotic
  • Best in catarrhal stage to alter clinical course
  • After paroxysmal stage: still treat to reduce transmission (5 days post-abx no longer contagious)
  • Macrolide first-line:
    • Azithromycin 500 mg day 1 → 250 mg qd day 2-5 (10 mg/kg day 1 → 5 mg/kg day 2-5 for kids)
    • Clarithromycin 500 mg bid × 7d
    • Erythromycin 14d (worst tolerated, GI side effects)
  • Alt: TMP-SMX 14d (macrolide allergy / R / azithro 倱敗)
  • Newborn infant ≀ 1 month — erythromycin associated with pyloric stenosis; azithromycin 偏奜
178.1.0.7.2 B. Supportive
  • Hospitalization for: < 6 mo, severe paroxysm, apnea, hypoxia, pneumonia, encephalopathy
  • O2, suction, ICU monitoring
  • IVF, nutrition
  • Bronchodilators / steroids — no clear benefit (some try)
  • Exchange transfusion + ECMO for severe pulmonary HTN in critical infants
178.1.0.7.3 C. Contact Prophylaxis
  • Household contact + close contact (face-to-face, > 1 hr) + healthcare workers
  • Azithromycin same dose as treatment within 21 days of exposure
  • Tdap booster if not had recently

178.1.0.8 7⃣ Prevention

178.1.0.8.1 Vaccine Schedule (ACIP 2024)
  • DTaP: 2 / 4 / 6 / 15-18 mo + 4-6 yr (5 doses) — pediatric
  • Tdap: 11-12 yr + 1 in adulthood + 每次 pregnancy 27-36 wk
  • Td booster: q10y (Td or Tdap)
178.1.0.8.2 Pregnancy Tdap
  • Each pregnancy 27-36 wk (regardless of prior)
  • Maternal Ab → passive immunity to newborn
  • ≥ 80% reduction in infant pertussis < 6 mo
  • Most important single intervention for infant protection
178.1.0.8.3 “Cocooning” Strategy
  • All household contacts + healthcare workers + caregivers — Tdap up to date
  • Reduces infant transmission