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)

Welcome to EM@3AM, an emDOCs series designed to foster your working knowledge by providing an expedited review of clinical basics. We’ll keep it short, while you keep that EM brain sharp.

A 3-month-old male presents to the ED with persistent fever, decreased oral intake, and worsening cough associated with post-tussive emesis for the five days. Parents state that the patient’s older sibling has had similar symptoms for the past two weeks and that neither child has received vaccinations after birth. The patient presents with BP 98/64 mm Hg, HR 160, RR 62, T 38.1ºC. Physical exam demonstrates an ill-appearing infant with bilateral conjunctival hemorrhage, dry cough, and inspiratory “whooping” sound.

What is the most likely cause of this patient’s symptoms and what are the next steps in management?

Answer: Pertussis



  • 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.



  • 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



  • 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



  • 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]



  • 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


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