EM@3AM: Pertussis

Author: Vivek Medepalli, MD (EM Resident Physician, UTSW / Parkland Memorial Hospital) // Reviewed by: Brit Long, MD (@long_brit, EM Attending Physician, San Antonio, TX), Zachary Aust, MD (EM Attending Physician, UTSW / Parkland Memorial Hospital) and Alex Koyfman, MD (@EMHighAK, EM Attending Physician, UTSW / Parkland Memorial Hospital)

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Answer: Pertussis

Epidemiology:

• Higher rates of infection in young infants (less than 6 months age) due to unvaccinated status ^[1]
• Incidence rising since the early 1990s despite widespread vaccination ^[1]
  • Immunization requires booster every 10 years; waning immunity can be a risk for infection
• Incubation period of is approximately 7-10 days.

Pathophysiology:

• Caused by Bordetella Pertussis ^[1]
  • Gram negative coccobacillus that produces pertussis toxin
  • Pertussis toxin can cause decreased immune response
• Transmission due to person-to-person contact with respiratory droplets or airborne droplets ^[1]
  • Can also be transmitted through fomites
• Symptoms due to increased secretions within the respiratory tract ^[3]
  • Bacteria accumulates within the ciliary epithelial cells of respiratory mucosa
  • The production of virulent factors can cause diminished function of respiratory ciliary epithelium
• Pertussis toxin can also lead to other systemic symptoms including lymphocytosis and metabolic derangements

Clinical Features and Disease Course:

• Several stages are associated with this disease
• Incubation period: days to weeks
• Catarrhal Stage (Week 1-2) ^[2]
  • Generalized upper respiratory symptoms: worsening dry cough, rhinorrhea, conjunctival injection, malaise
  • Low grade fever occasionally seen
  • Highest period of infectivity
• Paroxysmal Phase (Week 2-6) ^[2]
  • “Paroxysmal” refers to the intermittent intense dry coughing during this phase followed by high-pitched inspiratory “whoop.”
    • Symptoms are more common at nighttime
    • Inspiratory whoop was seen in approximately 79% of unvaccinated children ^[3] and 22-44% of vaccinated children ^[4]
  • Infants can present as apnea with this phase
  • Can be accompanied by choking, gagging, or cyanosis in infants with very little inspiratory effort.
  • Forceful expulsion of mucus is often followed by post-tussive emesis.
  • Intense coughing can lead to other sequelae, including conjunctival hemorrhage and petechiae
• Convalescent Phase (Weeks to Months)
  • Progressive, gradual reduction of symptoms with residual coughing

Workup and Laboratory Findings:

• General workup ^[1]
  • CBC
  • Bordetella Pertussis PCR
  • +/- CXR
• Lymphocytosis
  • Absolute lymphocyte count often ≥ 10,000 ^[1]
  • WBC and lymphocyte count can be used to determine disease severity in infants
    • ≥ 60,000 associated with increased severity, pneumonia, and pulmonary hypertension ^[5]
    • Rise of lymphocyte count to ≥ 30,000 five days after onset of cough associated with increased severity and death ^[2]
  • Imaging generally shows nonspecific findings, including peribronchial cuffing and atelectasis
  • Pertussis PCR via nasopharyngeal swab can identify bacteria in 3-7 days ^[2]

Differential Diagnosis: ^[2]

• Bronchiolitis
• Croup
• Pneumonia
• COVID-19
• Allergic reaction
• Other viral URI, commonly due to adenovirus, rhinovirus, human metapneumovirus

Complications:

• Pneumonia
• Respiratory failure
• Infants < 3 months: Mortality 1-3% ^[3]
  • Increased risk in premature infants and patients with underlying cardiopulmonary disease
• Good prognosis if > 3 months

Treatment:

• Antibiotics reduce infectivity but do not reduce severity or severity of the disease
• Early macrolide therapy (azithromycin, erythromycin, clarithromycin) ^[2]
  • Macrolides typically indicated within the first three weeks of symptoms (catarrhal and early paroxysmal phases)
  • Adult Dosing: Azithromycin (5-day “Z-Pack”): 500mg QD day 1, 250mg QD day 2-5
    • If allergic to macrolides, trimethoprim-sulfamethoxazole can be used
  • Antibiotic therapy not commonly recommended beyond three weeks of symptoms
    • Paroxysmal cough at this stage is primarily due to tissue damage rather than active bacterial infection
  • Exception: Macrolides recommended up to 6 weeks after symptom onset in pregnant patients ^[1]

Post-Exposure Prophylaxis and Isolation:

• Post-exposure prophylaxis with macrolide is indicated in all household contacts with macrolide therapy
  • Azithromycin 500mg QD day 1, 250mg QD day 2-5 ^[2]
• Isolation period required for 5 days following initiation of antibiotics or three weeks after onset of symptoms in patients who did not receive antibiotics ^[2]

Vaccination and Prevention:

• Routine immunization schedule with DTaP vaccine (diphtheria, tetanus, acellular pertussis) in five doses ^[2]
  • 2, 4, 6 months with booster at 15-18 months and 4-6 years
• Additional booster vaccination with Tdap at 11-18 years of age with repeat boosters every 10 years ^[2]

Disposition:

• Patients under 6 months old are often admitted due to increased morbidity/mortality. ^[3]
  • 86% of hospital admissions are in patients under 3 months of age ^[5]
• Low threshold to admit if < 1 year old with concerning respiratory symptoms or dehydration ^[3]
• ICU admission if apneic, hemodynamically unstable (bradycardia/hypotension), seizures, altered mental status, hyperleukocytosis ^[3]
  • WBC > 100,000 associated with worse outcome, possible need for leukoreduction therapy ^[9]

Summary and Pearls:

• Consider pertussis for patients with respiratory illness lasting longer than two weeks with slow improvement in symptoms over months.
  • Consider in unvaccinated infants with prolonged respiratory symptoms and paroxysmal cough with inspiratory “whoop”
• Increased morbidity and mortality in infants < 6 months of age due to unvaccinated status
• Three phases: Catarrhal, Paroxysmal, Convalescent
• Workup: Labs may show reveal profound lymphocytosis, imaging is generally nonspecific
• Treatment and Post-Exposure Prophylaxis: Macrolide (ex. Azithromycin)
• Prevention: DTaP (children), Tdap (adolescents, adults)
• Disposition: Admission recommended for infants < 6 months, ICU if apnea, hemodynamic instability, seizures, hyperleukocytosis

References