Confusable diagnoses · PANCE / PANRE

Bronchiolitis vs Pertussis

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

Bronchiolitis and Pertussis are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.

Bronchiolitis vs Pertussis at a glance

  • Bronchiolitis: Viral lower respiratory tract infection of infants causing wheeze, hypoxia, and dehydration.
  • Pertussis: Bordetella pertussis respiratory infection with paroxysmal cough and inspiratory whoop.

Try two board-style questions on Bronchiolitis vs Pertussis

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Question 1PulmonaryMedium
A 5-month-old infant has rhinorrhea, cough, wheezing, and mild subcostal retractions during winter. Oxygen saturation is 96% and feeding is adequate. Which of the following is the most appropriate management?
  • AOral prednisone for five days
  • BScheduled albuterol nebulizer treatments
  • CEmpiric oral amoxicillin therapy
  • DSupportive care with nasal suctioning
Reveal answer & full explanation
Correct answer: D — Supportive care with nasal suctioning
  • AOral prednisone for five days
  • BScheduled albuterol nebulizer treatments
  • CEmpiric oral amoxicillin therapy
  • DSupportive care with nasal suctioning✓

Why Supportive care with nasal suctioning is correct

  • Bronchiolitis is a viral lower-airway infection (most often RSV) managed supportively when oxygenation and feeding are maintained.
  • Nasal suctioning clears obstructing secretions and adequate hydration supports the infant through the illness.
  • With saturation of 96% and adequate feeding, no pharmacologic therapy is indicated.

Why the others are wrong

  • Scheduled albuterol nebulizer treatments — Bronchodilators do not change the course of bronchiolitis because the wheeze is from plugging and edema, not reversible bronchospasm; it baits an asthma-treatment reflex.
  • Oral prednisone for five days — Corticosteroids are not effective in bronchiolitis and are not recommended.
  • Empiric oral amoxicillin therapy — The illness is viral, so antibiotics add no benefit without evidence of a bacterial complication.
Question 2PulmonaryMedium
A 5-week-old unvaccinated infant is brought to the emergency department after two episodes of turning blue at home. The mother reports 10 days of nasal congestion followed by sudden coughing fits, and an older sibling has had a lingering cough for 3 weeks. The infant is afebrile with intermittent apneic spells; between episodes she appears well. A nasopharyngeal swab is sent for Bordetella pertussis PCR. Which of the following laboratory findings would best support the suspected diagnosis?
  • APeripheral eosinophilia over 1,500 cells/microL
  • BLeukopenia with lymphopenia and mild thrombocytopenia
  • CNeutrophilic leukocytosis with marked bandemia
  • DMarked lymphocytosis with WBC over 20,000/microL
Reveal answer & full explanation
Correct answer: D — Marked lymphocytosis with WBC over 20,000/microL
  • APeripheral eosinophilia over 1,500 cells/microL
  • BLeukopenia with lymphopenia and mild thrombocytopenia
  • CNeutrophilic leukocytosis with marked bandemia
  • DMarked lymphocytosis with WBC over 20,000/microL✓

Why Marked lymphocytosis with WBC over 20,000/microL is correct

  • Pertussis toxin impairs lymphocyte egress from the circulation, producing a characteristic marked lymphocytosis; a CBC showing WBC over 20,000/microL with lymphocyte predominance strongly supports pertussis, especially in infants and unvaccinated children.
  • The degree of lymphocytosis correlates with disease severity and, when extreme, with the risk of pulmonary hypertension and death in young infants.
  • This pattern, in the setting of catarrhal symptoms progressing to paroxysmal cough and apnea with a sick contact, is the supporting finding while PCR (the most sensitive confirmatory test in the first 3-4 weeks) is pending.

Why the others are wrong

  • Neutrophilic leukocytosis with marked bandemia — suggests a pyogenic bacterial infection such as a secondary bacterial pneumonia; pertussis classically drives a lymphocyte-predominant, not neutrophil-predominant, count.
  • Peripheral eosinophilia over 1,500 cells/microL — points toward atopic or parasitic processes, not pertussis, which does not cause eosinophilia.
  • Leukopenia with lymphopenia and mild thrombocytopenia — is the expected pattern in many acute viral respiratory infections that can mimic the catarrhal prodrome; pertussis toxin blocks lymphocytes from leaving the circulation, so the count rises rather than falls.
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Side-by-side comparison

FeatureBronchiolitisPertussis
At a glanceViral lower respiratory tract infection of infants causing wheeze, hypoxia, and dehydration.Bordetella pertussis respiratory infection with paroxysmal cough and inspiratory whoop.
Classic presentation1-3 days of URI symptoms (rhinorrhea, cough, low-grade fever); Progression to lower respiratory tract: tachypnea, wheeze, cough, increased work of breathing; Poor feeding, dehydration; Apnea (especially in infants <2 months or preterm); Symptoms peak day 3-5, resolve over 1-2 weeks; Tachypnea, nasal flaring, retractions (subcostal,…Paroxysmal coughing fits with inspiratory whoop and post-tussive emesis lasting >2 weeks in a child or adolescent. Apnea (not cough) in young infant.; Catarrhal phase (1-2 weeks): mild URI symptoms — rhinorrhea, low-grade fever, mild cough; most contagious period; Paroxysmal phase (2-8 weeks): sudden severe coughing fits ending with…
Workup / key labsClinical diagnosis — routine viral testing NOT recommended in typical cases (does not change management); RSV testing may help with cohorting or public health surveillance; Pulse oximetry to assess hypoxia; Consider CBC, BMP, and blood cultures only if febrile neonate (<28 days), toxic appearance, or sepsis concern (very rare bacterial…CDC/CSTE 2020 case definition: in the absence of a more likely diagnosis, cough lasting ≥2 weeks with at least one of paroxysms, inspiratory whoop, post-tussive emesis, or apnea (with or without cyanosis). Confirmed case: acute cough of any duration with a positive culture or PCR for B. pertussis (serology is not a confirmatory…
ImagingChest radiograph NOT routinely recommended (AAP 2014) — risk of overdiagnosis of pneumonia and unnecessary antibiotics; Obtain CXR if focal exam findings, severe disease, fails to improve, or alternative diagnosis suspected — findings: hyperinflation, peribronchial thickening, atelectasisChest radiograph: often normal or shows perihilar infiltrate ('shaggy heart border'); rules out pneumonia and other complications
First-line treatmentSupportive care — cornerstone:; Suction nasal secretions (gentle bulb suction before feeds; deep suction NOT recommended); Hydration: oral/NG feeds if tolerated; IV fluids if severe respiratory distress or unable to feed; Supplemental oxygen for SpO2 <90% (AAP 2014; lowered threshold avoids unnecessary admission); Antipyretics for…Antibiotic treatment primarily REDUCES TRANSMISSION; clinical benefit greatest if started in catarrhal or early paroxysmal phase; Macrolide first-line:; Azithromycin: infants <1 month 10 mg/kg/day × 5 days; infants 1-5 months same dose; children ≥6 months 10 mg/kg (max 500 mg) day 1 then 5 mg/kg (max 250 mg) days 2-5; adolescents/adults…

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Full outlines

Bronchiolitis (RSV) Pertussis (Whooping Cough) All 514 diagnoses

Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.